diff options
| author |   Jonathan Corbet <corbet@lwn.net> | 2016-11-18 16:19:28 -0700 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2016-11-18 16:19:28 -0700 |
| commit | 726d661fea3e3f76d36515c74e4ce58e7789418e (patch) | |
| tree | 0f996a1d5c0cca796b135378beb66e9829fae854 /Documentation/DocBook | |
| parent | Merge tag 'v4.9-rc4' into sound (diff) | |
| parent | ASoC: doc: ReSTize codec_to_codec.txt (diff) | |
| download | linux-dev-726d661fea3e3f76d36515c74e4ce58e7789418e.tar.xz linux-dev-726d661fea3e3f76d36515c74e4ce58e7789418e.zip | |
Merge remote-tracking branch 'sound/topic/restize-docs' into sound
Bring in the sphinxification of the sound documentation.
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 3 | ||||
| -rw-r--r-- | Documentation/DocBook/alsa-driver-api.tmpl | 142 | ||||
| -rw-r--r-- | Documentation/DocBook/writing-an-alsa-driver.tmpl | 6206 |
3 files changed, 1 insertions, 6350 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 857b772e9da1..c8bd257660eb 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -12,8 +12,7 @@ DOCBOOKS := z8530book.xml \ kernel-api.xml filesystems.xml lsm.xml kgdb.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ - debugobjects.xml sh.xml regulator.xml \ - alsa-driver-api.xml writing-an-alsa-driver.xml \ + 80211.xml debugobjects.xml sh.xml regulator.xml \ tracepoint.xml w1.xml \ writing_musb_glue_layer.xml crypto-API.xml iio.xml diff --git a/Documentation/DocBook/alsa-driver-api.tmpl b/Documentation/DocBook/alsa-driver-api.tmpl deleted file mode 100644 index 53f439dcc94b..000000000000 --- a/Documentation/DocBook/alsa-driver-api.tmpl +++ /dev/null @@ -1,142 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> - -<!-- ****************************************************** --> -<!-- Header --> -<!-- ****************************************************** --> -<book id="ALSA-Driver-API"> - <bookinfo> - <title>The ALSA Driver API</title> - - <legalnotice> - <para> - This document is free; you can redistribute it and/or modify it - under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 2 of the License, or - (at your option) any later version. - </para> - - <para> - This document is distributed in the hope that it will be useful, - but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the - implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A - PARTICULAR PURPOSE</emphasis>. See the GNU General Public License - for more details. - </para> - - <para> - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - </para> - </legalnotice> - - </bookinfo> - -<toc></toc> - - <chapter><title>Management of Cards and Devices</title> - <sect1><title>Card Management</title> -!Esound/core/init.c - </sect1> - <sect1><title>Device Components</title> -!Esound/core/device.c - </sect1> - <sect1><title>Module requests and Device File Entries</title> -!Esound/core/sound.c - </sect1> - <sect1><title>Memory Management Helpers</title> -!Esound/core/memory.c -!Esound/core/memalloc.c - </sect1> - </chapter> - <chapter><title>PCM API</title> - <sect1><title>PCM Core</title> -!Esound/core/pcm.c -!Esound/core/pcm_lib.c -!Esound/core/pcm_native.c -!Iinclude/sound/pcm.h - </sect1> - <sect1><title>PCM Format Helpers</title> -!Esound/core/pcm_misc.c - </sect1> - <sect1><title>PCM Memory Management</title> -!Esound/core/pcm_memory.c - </sect1> - <sect1><title>PCM DMA Engine API</title> -!Esound/core/pcm_dmaengine.c -!Iinclude/sound/dmaengine_pcm.h - </sect1> - </chapter> - <chapter><title>Control/Mixer API</title> - <sect1><title>General Control Interface</title> -!Esound/core/control.c - </sect1> - <sect1><title>AC97 Codec API</title> -!Esound/pci/ac97/ac97_codec.c -!Esound/pci/ac97/ac97_pcm.c - </sect1> - <sect1><title>Virtual Master Control API</title> -!Esound/core/vmaster.c -!Iinclude/sound/control.h - </sect1> - </chapter> - <chapter><title>MIDI API</title> - <sect1><title>Raw MIDI API</title> -!Esound/core/rawmidi.c - </sect1> - <sect1><title>MPU401-UART API</title> -!Esound/drivers/mpu401/mpu401_uart.c - </sect1> - </chapter> - <chapter><title>Proc Info API</title> - <sect1><title>Proc Info Interface</title> -!Esound/core/info.c - </sect1> - </chapter> - <chapter><title>Compress Offload</title> - <sect1><title>Compress Offload API</title> -!Esound/core/compress_offload.c -!Iinclude/uapi/sound/compress_offload.h -!Iinclude/uapi/sound/compress_params.h -!Iinclude/sound/compress_driver.h - </sect1> - </chapter> - <chapter><title>ASoC</title> - <sect1><title>ASoC Core API</title> -!Iinclude/sound/soc.h -!Esound/soc/soc-core.c -<!-- !Esound/soc/soc-cache.c no docbook comments here --> -!Esound/soc/soc-devres.c -!Esound/soc/soc-io.c -!Esound/soc/soc-pcm.c -!Esound/soc/soc-ops.c -!Esound/soc/soc-compress.c - </sect1> - <sect1><title>ASoC DAPM API</title> -!Esound/soc/soc-dapm.c - </sect1> - <sect1><title>ASoC DMA Engine API</title> -!Esound/soc/soc-generic-dmaengine-pcm.c - </sect1> - </chapter> - <chapter><title>Miscellaneous Functions</title> - <sect1><title>Hardware-Dependent Devices API</title> -!Esound/core/hwdep.c - </sect1> - <sect1><title>Jack Abstraction Layer API</title> -!Iinclude/sound/jack.h -!Esound/core/jack.c -!Esound/soc/soc-jack.c - </sect1> - <sect1><title>ISA DMA Helpers</title> -!Esound/core/isadma.c - </sect1> - <sect1><title>Other Helper Macros</title> -!Iinclude/sound/core.h - </sect1> - </chapter> - -</book> diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl deleted file mode 100644 index a27ab9f53fb6..000000000000 --- a/Documentation/DocBook/writing-an-alsa-driver.tmpl +++ /dev/null @@ -1,6206 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> - -<!-- ****************************************************** --> -<!-- Header --> -<!-- ****************************************************** --> -<book id="Writing-an-ALSA-Driver"> - <bookinfo> - <title>Writing an ALSA Driver</title> - <author> - <firstname>Takashi</firstname> - <surname>Iwai</surname> - <affiliation> - <address> - <email>tiwai@suse.de</email> - </address> - </affiliation> - </author> - - <date>Oct 15, 2007</date> - <edition>0.3.7</edition> - - <abstract> - <para> - This document describes how to write an ALSA (Advanced Linux - Sound Architecture) driver. - </para> - </abstract> - - <legalnotice> - <para> - Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email> - </para> - - <para> - This document is free; you can redistribute it and/or modify it - under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 2 of the License, or - (at your option) any later version. - </para> - - <para> - This document is distributed in the hope that it will be useful, - but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the - implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A - PARTICULAR PURPOSE</emphasis>. See the GNU General Public License - for more details. - </para> - - <para> - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - </para> - </legalnotice> - - </bookinfo> - -<!-- ****************************************************** --> -<!-- Preface --> -<!-- ****************************************************** --> - <preface id="preface"> - <title>Preface</title> - <para> - This document describes how to write an - <ulink url="http://www.alsa-project.org/"><citetitle> - ALSA (Advanced Linux Sound Architecture)</citetitle></ulink> - driver. The document focuses mainly on PCI soundcards. - In the case of other device types, the API might - be different, too. However, at least the ALSA kernel API is - consistent, and therefore it would be still a bit help for - writing them. - </para> - - <para> - This document targets people who already have enough - C language skills and have basic linux kernel programming - knowledge. This document doesn't explain the general - topic of linux kernel coding and doesn't cover low-level - driver implementation details. It only describes - the standard way to write a PCI sound driver on ALSA. - </para> - - <para> - If you are already familiar with the older ALSA ver.0.5.x API, you - can check the drivers such as <filename>sound/pci/es1938.c</filename> or - <filename>sound/pci/maestro3.c</filename> which have also almost the same - code-base in the ALSA 0.5.x tree, so you can compare the differences. - </para> - - <para> - This document is still a draft version. Any feedback and - corrections, please!! - </para> - </preface> - - -<!-- ****************************************************** --> -<!-- File Tree Structure --> -<!-- ****************************************************** --> - <chapter id="file-tree"> - <title>File Tree Structure</title> - - <section id="file-tree-general"> - <title>General</title> - <para> - The ALSA drivers are provided in two ways. - </para> - - <para> - One is the trees provided as a tarball or via cvs from the - ALSA's ftp site, and another is the 2.6 (or later) Linux kernel - tree. To synchronize both, the ALSA driver tree is split into - two different trees: alsa-kernel and alsa-driver. The former - contains purely the source code for the Linux 2.6 (or later) - tree. This tree is designed only for compilation on 2.6 or - later environment. The latter, alsa-driver, contains many subtle - files for compiling ALSA drivers outside of the Linux kernel tree, - wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API, - and additional drivers which are still in development or in - tests. The drivers in alsa-driver tree will be moved to - alsa-kernel (and eventually to the 2.6 kernel tree) when they are - finished and confirmed to work fine. - </para> - - <para> - The file tree structure of ALSA driver is depicted below. Both - alsa-kernel and alsa-driver have almost the same file - structure, except for <quote>core</quote> directory. It's - named as <quote>acore</quote> in alsa-driver tree. - - <example> - <title>ALSA File Tree Structure</title> - <literallayout> - sound - /core - /oss - /seq - /oss - /instr - /ioctl32 - /include - /drivers - /mpu401 - /opl3 - /i2c - /l3 - /synth - /emux - /pci - /(cards) - /isa - /(cards) - /arm - /ppc - /sparc - /usb - /pcmcia /(cards) - /oss - </literallayout> - </example> - </para> - </section> - - <section id="file-tree-core-directory"> - <title>core directory</title> - <para> - This directory contains the middle layer which is the heart - of ALSA drivers. In this directory, the native ALSA modules are - stored. The sub-directories contain different modules and are - dependent upon the kernel config. - </para> - - <section id="file-tree-core-directory-oss"> - <title>core/oss</title> - - <para> - The codes for PCM and mixer OSS emulation modules are stored - in this directory. The rawmidi OSS emulation is included in - the ALSA rawmidi code since it's quite small. The sequencer - code is stored in <filename>core/seq/oss</filename> directory (see - <link linkend="file-tree-core-directory-seq-oss"><citetitle> - below</citetitle></link>). - </para> - </section> - - <section id="file-tree-core-directory-ioctl32"> - <title>core/ioctl32</title> - - <para> - This directory contains the 32bit-ioctl wrappers for 64bit - architectures such like x86-64, ppc64 and sparc64. For 32bit - and alpha architectures, these are not compiled. - </para> - </section> - - <section id="file-tree-core-directory-seq"> - <title>core/seq</title> - <para> - This directory and its sub-directories are for the ALSA - sequencer. This directory contains the sequencer core and - primary sequencer modules such like snd-seq-midi, - snd-seq-virmidi, etc. They are compiled only when - <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel - config. - </para> - </section> - - <section id="file-tree-core-directory-seq-oss"> - <title>core/seq/oss</title> - <para> - This contains the OSS sequencer emulation codes. - </para> - </section> - - <section id="file-tree-core-directory-deq-instr"> - <title>core/seq/instr</title> - <para> - This directory contains the modules for the sequencer - instrument layer. - </para> - </section> - </section> - - <section id="file-tree-include-directory"> - <title>include directory</title> - <para> - This is the place for the public header files of ALSA drivers, - which are to be exported to user-space, or included by - several files at different directories. Basically, the private - header files should not be placed in this directory, but you may - still find files there, due to historical reasons :) - </para> - </section> - - <section id="file-tree-drivers-directory"> - <title>drivers directory</title> - <para> - This directory contains code shared among different drivers - on different architectures. They are hence supposed not to be - architecture-specific. - For example, the dummy pcm driver and the serial MIDI - driver are found in this directory. In the sub-directories, - there is code for components which are independent from - bus and cpu architectures. - </para> - - <section id="file-tree-drivers-directory-mpu401"> - <title>drivers/mpu401</title> - <para> - The MPU401 and MPU401-UART modules are stored here. - </para> - </section> - - <section id="file-tree-drivers-directory-opl3"> - <title>drivers/opl3 and opl4</title> - <para> - The OPL3 and OPL4 FM-synth stuff is found here. - </para> - </section> - </section> - - <section id="file-tree-i2c-directory"> - <title>i2c directory</title> - <para> - This contains the ALSA i2c components. - </para> - - <para> - Although there is a standard i2c layer on Linux, ALSA has its - own i2c code for some cards, because the soundcard needs only a - simple operation and the standard i2c API is too complicated for - such a purpose. - </para> - - <section id="file-tree-i2c-directory-l3"> - <title>i2c/l3</title> - <para> - This is a sub-directory for ARM L3 i2c. - </para> - </section> - </section> - - <section id="file-tree-synth-directory"> - <title>synth directory</title> - <para> - This contains the synth middle-level modules. - </para> - - <para> - So far, there is only Emu8000/Emu10k1 synth driver under - the <filename>synth/emux</filename> sub-directory. - </para> - </section> - - <section id="file-tree-pci-directory"> - <title>pci directory</title> - <para> - This directory and its sub-directories hold the top-level card modules - for PCI soundcards and the code specific to the PCI BUS. - </para> - - <para> - The drivers compiled from a single file are stored directly - in the pci directory, while the drivers with several source files are - stored on their own sub-directory (e.g. emu10k1, ice1712). - </para> - </section> - - <section id="file-tree-isa-directory"> - <title>isa directory</title> - <para> - This directory and its sub-directories hold the top-level card modules - for ISA soundcards. - </para> - </section> - - <section id="file-tree-arm-ppc-sparc-directories"> - <title>arm, ppc, and sparc directories</title> - <para> - They are used for top-level card modules which are - specific to one of these architectures. - </para> - </section> - - <section id="file-tree-usb-directory"> - <title>usb directory</title> - <para> - This directory contains the USB-audio driver. In the latest version, the - USB MIDI driver is integrated in the usb-audio driver. - </para> - </section> - - <section id="file-tree-pcmcia-directory"> - <title>pcmcia directory</title> - <para> - The PCMCIA, especially PCCard drivers will go here. CardBus - drivers will be in the pci directory, because their API is identical - to that of standard PCI cards. - </para> - </section> - - <section id="file-tree-oss-directory"> - <title>oss directory</title> - <para> - The OSS/Lite source files are stored here in Linux 2.6 (or - later) tree. In the ALSA driver tarball, this directory is empty, - of course :) - </para> - </section> - </chapter> - - -<!-- ****************************************************** --> -<!-- Basic Flow for PCI Drivers --> -<!-- ****************************************************** --> - <chapter id="basic-flow"> - <title>Basic Flow for PCI Drivers</title> - - <section id="basic-flow-outline"> - <title>Outline</title> - <para> - The minimum flow for PCI soundcards is as follows: - - <itemizedlist> - <listitem><para>define the PCI ID table (see the section - <link linkend="pci-resource-entries"><citetitle>PCI Entries - </citetitle></link>).</para></listitem> - <listitem><para>create <function>probe()</function> callback.</para></listitem> - <listitem><para>create <function>remove()</function> callback.</para></listitem> - <listitem><para>create a <structname>pci_driver</structname> structure - containing the three pointers above.</para></listitem> - <listitem><para>create an <function>init()</function> function just calling - the <function>pci_register_driver()</function> to register the pci_driver table - defined above.</para></listitem> - <listitem><para>create an <function>exit()</function> function to call - the <function>pci_unregister_driver()</function> function.</para></listitem> - </itemizedlist> - </para> - </section> - - <section id="basic-flow-example"> - <title>Full Code Example</title> - <para> - The code example is shown below. Some parts are kept - unimplemented at this moment but will be filled in the - next sections. The numbers in the comment lines of the - <function>snd_mychip_probe()</function> function - refer to details explained in the following section. - - <example> - <title>Basic Flow for PCI Drivers - Example</title> - <programlisting> -<![CDATA[ - #include <linux/init.h> - #include <linux/pci.h> - #include <linux/slab.h> - #include <sound/core.h> - #include <sound/initval.h> - - /* module parameters (see "Module Parameters") */ - /* SNDRV_CARDS: maximum number of cards supported by this module */ - static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; - static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; - static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; - - /* definition of the chip-specific record */ - struct mychip { - struct snd_card *card; - /* the rest of the implementation will be in section - * "PCI Resource Management" - */ - }; - - /* chip-specific destructor - * (see "PCI Resource Management") - */ - static int snd_mychip_free(struct mychip *chip) - { - .... /* will be implemented later... */ - } - - /* component-destructor - * (see "Management of Cards and Components") - */ - static int snd_mychip_dev_free(struct snd_device *device) - { - return snd_mychip_free(device->device_data); - } - - /* chip-specific constructor - * (see "Management of Cards and Components") - */ - static int snd_mychip_create(struct snd_card *card, - struct pci_dev *pci, - struct mychip **rchip) - { - struct mychip *chip; - int err; - static struct snd_device_ops ops = { - .dev_free = snd_mychip_dev_free, - }; - - *rchip = NULL; - - /* check PCI availability here - * (see "PCI Resource Management") - */ - .... - - /* allocate a chip-specific data with zero filled */ - chip = kzalloc(sizeof(*chip), GFP_KERNEL); - if (chip == NULL) - return -ENOMEM; - - chip->card = card; - - /* rest of initialization here; will be implemented - * later, see "PCI Resource Management" - */ - .... - - err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); - if (err < 0) { - snd_mychip_free(chip); - return err; - } - - *rchip = chip; - return 0; - } - - /* constructor -- see "Constructor" sub-section */ - static int snd_mychip_probe(struct pci_dev *pci, - const struct pci_device_id *pci_id) - { - static int dev; - struct snd_card *card; - struct mychip *chip; - int err; - - /* (1) */ - if (dev >= SNDRV_CARDS) - return -ENODEV; - if (!enable[dev]) { - dev++; - return -ENOENT; - } - - /* (2) */ - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - 0, &card); - if (err < 0) - return err; - - /* (3) */ - err = snd_mychip_create(card, pci, &chip); - if (err < 0) { - snd_card_free(card); - return err; - } - - /* (4) */ - strcpy(card->driver, "My Chip"); - strcpy(card->shortname, "My Own Chip 123"); - sprintf(card->longname, "%s at 0x%lx irq %i", - card->shortname, chip->ioport, chip->irq); - - /* (5) */ - .... /* implemented later */ - - /* (6) */ - err = snd_card_register(card); - if (err < 0) { - snd_card_free(card); - return err; - } - - /* (7) */ - pci_set_drvdata(pci, card); - dev++; - return 0; - } - - /* destructor -- see the "Destructor" sub-section */ - static void snd_mychip_remove(struct pci_dev *pci) - { - snd_card_free(pci_get_drvdata(pci)); - pci_set_drvdata(pci, NULL); - } -]]> - </programlisting> - </example> - </para> - </section> - - <section id="basic-flow-constructor"> - <title>Constructor</title> - <para> - The real constructor of PCI drivers is the <function>probe</function> callback. - The <function>probe</function> callback and other component-constructors which are called - from the <function>probe</function> callback cannot be used with - the <parameter>__init</parameter> prefix - because any PCI device could be a hotplug device. - </para> - - <para> - In the <function>probe</function> callback, the following scheme is often used. - </para> - - <section id="basic-flow-constructor-device-index"> - <title>1) Check and increment the device index.</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int dev; - .... - if (dev >= SNDRV_CARDS) - return -ENODEV; - if (!enable[dev]) { - dev++; - return -ENOENT; - } -]]> - </programlisting> - </informalexample> - - where enable[dev] is the module option. - </para> - - <para> - Each time the <function>probe</function> callback is called, check the - availability of the device. If not available, simply increment - the device index and returns. dev will be incremented also - later (<link - linkend="basic-flow-constructor-set-pci"><citetitle>step - 7</citetitle></link>). - </para> - </section> - - <section id="basic-flow-constructor-create-card"> - <title>2) Create a card instance</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - struct snd_card *card; - int err; - .... - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - 0, &card); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The details will be explained in the section - <link linkend="card-management-card-instance"><citetitle> - Management of Cards and Components</citetitle></link>. - </para> - </section> - - <section id="basic-flow-constructor-create-main"> - <title>3) Create a main component</title> - <para> - In this part, the PCI resources are allocated. - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip *chip; - .... - err = snd_mychip_create(card, pci, &chip); - if (err < 0) { - snd_card_free(card); - return err; - } -]]> - </programlisting> - </informalexample> - - The details will be explained in the section <link - linkend="pci-resource"><citetitle>PCI Resource - Management</citetitle></link>. - </para> - </section> - - <section id="basic-flow-constructor-main-component"> - <title>4) Set the driver ID and name strings.</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - strcpy(card->driver, "My Chip"); - strcpy(card->shortname, "My Own Chip 123"); - sprintf(card->longname, "%s at 0x%lx irq %i", - card->shortname, chip->ioport, chip->irq); -]]> - </programlisting> - </informalexample> - - The driver field holds the minimal ID string of the - chip. This is used by alsa-lib's configurator, so keep it - simple but unique. - Even the same driver can have different driver IDs to - distinguish the functionality of each chip type. - </para> - - <para> - The shortname field is a string shown as more verbose - name. The longname field contains the information - shown in <filename>/proc/asound/cards</filename>. - </para> - </section> - - <section id="basic-flow-constructor-create-other"> - <title>5) Create other components, such as mixer, MIDI, etc.</title> - <para> - Here you define the basic components such as - <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>, - mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>), - MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>), - and other interfaces. - Also, if you want a <link linkend="proc-interface"><citetitle>proc - file</citetitle></link>, define it here, too. - </para> - </section> - - <section id="basic-flow-constructor-register-card"> - <title>6) Register the card instance.</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - err = snd_card_register(card); - if (err < 0) { - snd_card_free(card); - return err; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - Will be explained in the section <link - linkend="card-management-registration"><citetitle>Management - of Cards and Components</citetitle></link>, too. - </para> - </section> - - <section id="basic-flow-constructor-set-pci"> - <title>7) Set the PCI driver data and return zero.</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - pci_set_drvdata(pci, card); - dev++; - return 0; -]]> - </programlisting> - </informalexample> - - In the above, the card record is stored. This pointer is - used in the remove callback and power-management - callbacks, too. - </para> - </section> - </section> - - <section id="basic-flow-destructor"> - <title>Destructor</title> - <para> - The destructor, remove callback, simply releases the card - instance. Then the ALSA middle layer will release all the - attached components automatically. - </para> - - <para> - It would be typically like the following: - - <informalexample> - <programlisting> -<![CDATA[ - static void snd_mychip_remove(struct pci_dev *pci) - { - snd_card_free(pci_get_drvdata(pci)); - pci_set_drvdata(pci, NULL); - } -]]> - </programlisting> - </informalexample> - - The above code assumes that the card pointer is set to the PCI - driver data. - </para> - </section> - - <section id="basic-flow-header-files"> - <title>Header Files</title> - <para> - For the above example, at least the following include files - are necessary. - - <informalexample> - <programlisting> -<![CDATA[ - #include <linux/init.h> - #include <linux/pci.h> - #include <linux/slab.h> - #include <sound/core.h> - #include <sound/initval.h> -]]> - </programlisting> - </informalexample> - - where the last one is necessary only when module options are - defined in the source file. If the code is split into several - files, the files without module options don't need them. - </para> - - <para> - In addition to these headers, you'll need - <filename><linux/interrupt.h></filename> for interrupt - handling, and <filename><asm/io.h></filename> for I/O - access. If you use the <function>mdelay()</function> or - <function>udelay()</function> functions, you'll need to include - <filename><linux/delay.h></filename> too. - </para> - - <para> - The ALSA interfaces like the PCM and control APIs are defined in other - <filename><sound/xxx.h></filename> header files. - They have to be included after - <filename><sound/core.h></filename>. - </para> - - </section> - </chapter> - - -<!-- ****************************************************** --> -<!-- Management of Cards and Components --> -<!-- ****************************************************** --> - <chapter id="card-management"> - <title>Management of Cards and Components</title> - - <section id="card-management-card-instance"> - <title>Card Instance</title> - <para> - For each soundcard, a <quote>card</quote> record must be allocated. - </para> - - <para> - A card record is the headquarters of the soundcard. It manages - the whole list of devices (components) on the soundcard, such as - PCM, mixers, MIDI, synthesizer, and so on. Also, the card - record holds the ID and the name strings of the card, manages - the root of proc files, and controls the power-management states - and hotplug disconnections. The component list on the card - record is used to manage the correct release of resources at - destruction. - </para> - - <para> - As mentioned above, to create a card instance, call - <function>snd_card_new()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_card *card; - int err; - err = snd_card_new(&pci->dev, index, id, module, extra_size, &card); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The function takes six arguments: the parent device pointer, - the card-index number, the id string, the module pointer (usually - <constant>THIS_MODULE</constant>), - the size of extra-data space, and the pointer to return the - card instance. The extra_size argument is used to - allocate card->private_data for the - chip-specific data. Note that these data - are allocated by <function>snd_card_new()</function>. - </para> - - <para> - The first argument, the pointer of struct - <structname>device</structname>, specifies the parent device. - For PCI devices, typically &pci-> is passed there. - </para> - </section> - - <section id="card-management-component"> - <title>Components</title> - <para> - After the card is created, you can attach the components - (devices) to the card instance. In an ALSA driver, a component is - represented as a struct <structname>snd_device</structname> object. - A component can be a PCM instance, a control interface, a raw - MIDI interface, etc. Each such instance has one component - entry. - </para> - - <para> - A component can be created via - <function>snd_device_new()</function> function. - - <informalexample> - <programlisting> -<![CDATA[ - snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); -]]> - </programlisting> - </informalexample> - </para> - - <para> - This takes the card pointer, the device-level - (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the - callback pointers (<parameter>&ops</parameter>). The - device-level defines the type of components and the order of - registration and de-registration. For most components, the - device-level is already defined. For a user-defined component, - you can use <constant>SNDRV_DEV_LOWLEVEL</constant>. - </para> - - <para> - This function itself doesn't allocate the data space. The data - must be allocated manually beforehand, and its pointer is passed - as the argument. This pointer (<parameter>chip</parameter> in the - above example) is used as the identifier for the instance. - </para> - - <para> - Each pre-defined ALSA component such as ac97 and pcm calls - <function>snd_device_new()</function> inside its - constructor. The destructor for each component is defined in the - callback pointers. Hence, you don't need to take care of - calling a destructor for such a component. - </para> - - <para> - If you wish to create your own component, you need to - set the destructor function to the dev_free callback in - the <parameter>ops</parameter>, so that it can be released - automatically via <function>snd_card_free()</function>. - The next example will show an implementation of chip-specific - data. - </para> - </section> - - <section id="card-management-chip-specific"> - <title>Chip-Specific Data</title> - <para> - Chip-specific information, e.g. the I/O port address, its - resource pointer, or the irq number, is stored in the - chip-specific record. - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip { - .... - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - In general, there are two ways of allocating the chip record. - </para> - - <section id="card-management-chip-specific-snd-card-new"> - <title>1. Allocating via <function>snd_card_new()</function>.</title> - <para> - As mentioned above, you can pass the extra-data-length - to the 5th argument of <function>snd_card_new()</function>, i.e. - - <informalexample> - <programlisting> -<![CDATA[ - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - sizeof(struct mychip), &card); -]]> - </programlisting> - </informalexample> - - struct <structname>mychip</structname> is the type of the chip record. - </para> - - <para> - In return, the allocated record can be accessed as - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip *chip = card->private_data; -]]> - </programlisting> - </informalexample> - - With this method, you don't have to allocate twice. - The record is released together with the card instance. - </para> - </section> - - <section id="card-management-chip-specific-allocate-extra"> - <title>2. Allocating an extra device.</title> - - <para> - After allocating a card instance via - <function>snd_card_new()</function> (with - <constant>0</constant> on the 4th arg), call - <function>kzalloc()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_card *card; - struct mychip *chip; - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - 0, &card); - ..... - chip = kzalloc(sizeof(*chip), GFP_KERNEL); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The chip record should have the field to hold the card - pointer at least, - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip { - struct snd_card *card; - .... - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - Then, set the card pointer in the returned chip instance. - - <informalexample> - <programlisting> -<![CDATA[ - chip->card = card; -]]> - </programlisting> - </informalexample> - </para> - - <para> - Next, initialize the fields, and register this chip - record as a low-level device with a specified - <parameter>ops</parameter>, - - <informalexample> - <programlisting> -<![CDATA[ - static struct snd_device_ops ops = { - .dev_free = snd_mychip_dev_free, - }; - .... - snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); -]]> - </programlisting> - </informalexample> - - <function>snd_mychip_dev_free()</function> is the - device-destructor function, which will call the real - destructor. - </para> - - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_mychip_dev_free(struct snd_device *device) - { - return snd_mychip_free(device->device_data); - } -]]> - </programlisting> - </informalexample> - - where <function>snd_mychip_free()</function> is the real destructor. - </para> - </section> - </section> - - <section id="card-management-registration"> - <title>Registration and Release</title> - <para> - After all components are assigned, register the card instance - by calling <function>snd_card_register()</function>. Access - to the device files is enabled at this point. That is, before - <function>snd_card_register()</function> is called, the - components are safely inaccessible from external side. If this - call fails, exit the probe function after releasing the card via - <function>snd_card_free()</function>. - </para> - - <para> - For releasing the card instance, you can call simply - <function>snd_card_free()</function>. As mentioned earlier, all - components are released automatically by this call. - </para> - - <para> - For a device which allows hotplugging, you can use - <function>snd_card_free_when_closed</function>. This one will - postpone the destruction until all devices are closed. - </para> - - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- PCI Resource Management --> -<!-- ****************************************************** --> - <chapter id="pci-resource"> - <title>PCI Resource Management</title> - - <section id="pci-resource-example"> - <title>Full Code Example</title> - <para> - In this section, we'll complete the chip-specific constructor, - destructor and PCI entries. Example code is shown first, - below. - - <example> - <title>PCI Resource Management Example</title> - <programlisting> -<![CDATA[ - struct mychip { - struct snd_card *card; - struct pci_dev *pci; - - unsigned long port; - int irq; - }; - - static int snd_mychip_free(struct mychip *chip) - { - /* disable hardware here if any */ - .... /* (not implemented in this document) */ - - /* release the irq */ - if (chip->irq >= 0) - free_irq(chip->irq, chip); - /* release the I/O ports & memory */ - pci_release_regions(chip->pci); - /* disable the PCI entry */ - pci_disable_device(chip->pci); - /* release the data */ - kfree(chip); - return 0; - } - - /* chip-specific constructor */ - static int snd_mychip_create(struct snd_card *card, - struct pci_dev *pci, - struct mychip **rchip) - { - struct mychip *chip; - int err; - static struct snd_device_ops ops = { - .dev_free = snd_mychip_dev_free, - }; - - *rchip = NULL; - - /* initialize the PCI entry */ - err = pci_enable_device(pci); - if (err < 0) - return err; - /* check PCI availability (28bit DMA) */ - if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || - pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { - printk(KERN_ERR "error to set 28bit mask DMA\n"); - pci_disable_device(pci); - return -ENXIO; - } - - chip = kzalloc(sizeof(*chip), GFP_KERNEL); - if (chip == NULL) { - pci_disable_device(pci); - return -ENOMEM; - } - - /* initialize the stuff */ - chip->card = card; - chip->pci = pci; - chip->irq = -1; - - /* (1) PCI resource allocation */ - err = pci_request_regions(pci, "My Chip"); - if (err < 0) { - kfree(chip); - pci_disable_device(pci); - return err; - } - chip->port = pci_resource_start(pci, 0); - if (request_irq(pci->irq, snd_mychip_interrupt, - IRQF_SHARED, KBUILD_MODNAME, chip)) { - printk(KERN_ERR "cannot grab irq %d\n", pci->irq); - snd_mychip_free(chip); - return -EBUSY; - } - chip->irq = pci->irq; - - /* (2) initialization of the chip hardware */ - .... /* (not implemented in this document) */ - - err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); - if (err < 0) { - snd_mychip_free(chip); - return err; - } - - *rchip = chip; - return 0; - } - - /* PCI IDs */ - static struct pci_device_id snd_mychip_ids[] = { - { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, - PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, - .... - { 0, } - }; - MODULE_DEVICE_TABLE(pci, snd_mychip_ids); - - /* pci_driver definition */ - static struct pci_driver driver = { - .name = KBUILD_MODNAME, - .id_table = snd_mychip_ids, - .probe = snd_mychip_probe, - .remove = snd_mychip_remove, - }; - - /* module initialization */ - static int __init alsa_card_mychip_init(void) - { - return pci_register_driver(&driver); - } - - /* module clean up */ - static void __exit alsa_card_mychip_exit(void) - { - pci_unregister_driver(&driver); - } - - module_init(alsa_card_mychip_init) - module_exit(alsa_card_mychip_exit) - - EXPORT_NO_SYMBOLS; /* for old kernels only */ -]]> - </programlisting> - </example> - </para> - </section> - - <section id="pci-resource-some-haftas"> - <title>Some Hafta's</title> - <para> - The allocation of PCI resources is done in the - <function>probe()</function> function, and usually an extra - <function>xxx_create()</function> function is written for this - purpose. - </para> - - <para> - In the case of PCI devices, you first have to call - the <function>pci_enable_device()</function> function before - allocating resources. Also, you need to set the proper PCI DMA - mask to limit the accessed I/O range. In some cases, you might - need to call <function>pci_set_master()</function> function, - too. - </para> - - <para> - Suppose the 28bit mask, and the code to be added would be like: - - <informalexample> - <programlisting> -<![CDATA[ - err = pci_enable_device(pci); - if (err < 0) - return err; - if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || - pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { - printk(KERN_ERR "error to set 28bit mask DMA\n"); - pci_disable_device(pci); - return -ENXIO; - } - -]]> - </programlisting> - </informalexample> - </para> - </section> - - <section id="pci-resource-resource-allocation"> - <title>Resource Allocation</title> - <para> - The allocation of I/O ports and irqs is done via standard kernel - functions. Unlike ALSA ver.0.5.x., there are no helpers for - that. And these resources must be released in the destructor - function (see below). Also, on ALSA 0.9.x, you don't need to - allocate (pseudo-)DMA for PCI like in ALSA 0.5.x. - </para> - - <para> - Now assume that the PCI device has an I/O port with 8 bytes - and an interrupt. Then struct <structname>mychip</structname> will have the - following fields: - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip { - struct snd_card *card; - - unsigned long port; - int irq; - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - For an I/O port (and also a memory region), you need to have - the resource pointer for the standard resource management. For - an irq, you have to keep only the irq number (integer). But you - need to initialize this number as -1 before actual allocation, - since irq 0 is valid. The port address and its resource pointer - can be initialized as null by - <function>kzalloc()</function> automatically, so you - don't have to take care of resetting them. - </para> - - <para> - The allocation of an I/O port is done like this: - - <informalexample> - <programlisting> -<![CDATA[ - err = pci_request_regions(pci, "My Chip"); - if (err < 0) { - kfree(chip); - pci_disable_device(pci); - return err; - } - chip->port = pci_resource_start(pci, 0); -]]> - </programlisting> - </informalexample> - </para> - - <para> - <!-- obsolete --> - It will reserve the I/O port region of 8 bytes of the given - PCI device. The returned value, chip->res_port, is allocated - via <function>kmalloc()</function> by - <function>request_region()</function>. The pointer must be - released via <function>kfree()</function>, but there is a - problem with this. This issue will be explained later. - </para> - - <para> - The allocation of an interrupt source is done like this: - - <informalexample> - <programlisting> -<![CDATA[ - if (request_irq(pci->irq, snd_mychip_interrupt, - IRQF_SHARED, KBUILD_MODNAME, chip)) { - printk(KERN_ERR "cannot grab irq %d\n", pci->irq); - snd_mychip_free(chip); - return -EBUSY; - } - chip->irq = pci->irq; -]]> - </programlisting> - </informalexample> - - where <function>snd_mychip_interrupt()</function> is the - interrupt handler defined <link - linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>. - Note that chip->irq should be defined - only when <function>request_irq()</function> succeeded. - </para> - - <para> - On the PCI bus, interrupts can be shared. Thus, - <constant>IRQF_SHARED</constant> is used as the interrupt flag of - <function>request_irq()</function>. - </para> - - <para> - The last argument of <function>request_irq()</function> is the - data pointer passed to the interrupt handler. Usually, the - chip-specific record is used for that, but you can use what you - like, too. - </para> - - <para> - I won't give details about the interrupt handler at this - point, but at least its appearance can be explained now. The - interrupt handler looks usually like the following: - - <informalexample> - <programlisting> -<![CDATA[ - static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) - { - struct mychip *chip = dev_id; - .... - return IRQ_HANDLED; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - Now let's write the corresponding destructor for the resources - above. The role of destructor is simple: disable the hardware - (if already activated) and release the resources. So far, we - have no hardware part, so the disabling code is not written here. - </para> - - <para> - To release the resources, the <quote>check-and-release</quote> - method is a safer way. For the interrupt, do like this: - - <informalexample> - <programlisting> -<![CDATA[ - if (chip->irq >= 0) - free_irq(chip->irq, chip); -]]> - </programlisting> - </informalexample> - - Since the irq number can start from 0, you should initialize - chip->irq with a negative value (e.g. -1), so that you can - check the validity of the irq number as above. - </para> - - <para> - When you requested I/O ports or memory regions via - <function>pci_request_region()</function> or - <function>pci_request_regions()</function> like in this example, - release the resource(s) using the corresponding function, - <function>pci_release_region()</function> or - <function>pci_release_regions()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - pci_release_regions(chip->pci); -]]> - </programlisting> - </informalexample> - </para> - - <para> - When you requested manually via <function>request_region()</function> - or <function>request_mem_region</function>, you can release it via - <function>release_resource()</function>. Suppose that you keep - the resource pointer returned from <function>request_region()</function> - in chip->res_port, the release procedure looks like: - - <informalexample> - <programlisting> -<![CDATA[ - release_and_free_resource(chip->res_port); -]]> - </programlisting> - </informalexample> - </para> - - <para> - Don't forget to call <function>pci_disable_device()</function> - before the end. - </para> - - <para> - And finally, release the chip-specific record. - - <informalexample> - <programlisting> -<![CDATA[ - kfree(chip); -]]> - </programlisting> - </informalexample> - </para> - - <para> - We didn't implement the hardware disabling part in the above. - If you need to do this, please note that the destructor may be - called even before the initialization of the chip is completed. - It would be better to have a flag to skip hardware disabling - if the hardware was not initialized yet. - </para> - - <para> - When the chip-data is assigned to the card using - <function>snd_device_new()</function> with - <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is - called at the last. That is, it is assured that all other - components like PCMs and controls have already been released. - You don't have to stop PCMs, etc. explicitly, but just - call low-level hardware stopping. - </para> - - <para> - The management of a memory-mapped region is almost as same as - the management of an I/O port. You'll need three fields like - the following: - - <informalexample> - <programlisting> -<![CDATA[ - struct mychip { - .... - unsigned long iobase_phys; - void __iomem *iobase_virt; - }; -]]> - </programlisting> - </informalexample> - - and the allocation would be like below: - - <informalexample> - <programlisting> -<![CDATA[ - if ((err = pci_request_regions(pci, "My Chip")) < 0) { - kfree(chip); - return err; - } - chip->iobase_phys = pci_resource_start(pci, 0); - chip->iobase_virt = ioremap_nocache(chip->iobase_phys, - pci_resource_len(pci, 0)); -]]> - </programlisting> - </informalexample> - - and the corresponding destructor would be: - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_mychip_free(struct mychip *chip) - { - .... - if (chip->iobase_virt) - iounmap(chip->iobase_virt); - .... - pci_release_regions(chip->pci); - .... - } -]]> - </programlisting> - </informalexample> - </para> - - </section> - - <section id="pci-resource-entries"> - <title>PCI Entries</title> - <para> - So far, so good. Let's finish the missing PCI - stuff. At first, we need a - <structname>pci_device_id</structname> table for this - chipset. It's a table of PCI vendor/device ID number, and some - masks. - </para> - - <para> - For example, - - <informalexample> - <programlisting> -<![CDATA[ - static struct pci_device_id snd_mychip_ids[] = { - { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, - PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, - .... - { 0, } - }; - MODULE_DEVICE_TABLE(pci, snd_mychip_ids); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The first and second fields of - the <structname>pci_device_id</structname> structure are the vendor and - device IDs. If you have no reason to filter the matching - devices, you can leave the remaining fields as above. The last - field of the <structname>pci_device_id</structname> struct contains - private data for this entry. You can specify any value here, for - example, to define specific operations for supported device IDs. - Such an example is found in the intel8x0 driver. - </para> - - <para> - The last entry of this list is the terminator. You must - specify this all-zero entry. - </para> - - <para> - Then, prepare the <structname>pci_driver</structname> record: - - <informalexample> - <programlisting> -<![CDATA[ - static struct pci_driver driver = { - .name = KBUILD_MODNAME, - .id_table = snd_mychip_ids, - .probe = snd_mychip_probe, - .remove = snd_mychip_remove, - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - The <structfield>probe</structfield> and - <structfield>remove</structfield> functions have already - been defined in the previous sections. - The <structfield>name</structfield> - field is the name string of this device. Note that you must not - use a slash <quote>/</quote> in this string. - </para> - - <para> - And at last, the module entries: - - <informalexample> - <programlisting> -<![CDATA[ - static int __init alsa_card_mychip_init(void) - { - return pci_register_driver(&driver); - } - - static void __exit alsa_card_mychip_exit(void) - { - pci_unregister_driver(&driver); - } - - module_init(alsa_card_mychip_init) - module_exit(alsa_card_mychip_exit) -]]> - </programlisting> - </informalexample> - </para> - - <para> - Note that these module entries are tagged with - <parameter>__init</parameter> and - <parameter>__exit</parameter> prefixes. - </para> - - <para> - Oh, one thing was forgotten. If you have no exported symbols, - you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels). - - <informalexample> - <programlisting> -<![CDATA[ - EXPORT_NO_SYMBOLS; -]]> - </programlisting> - </informalexample> - - That's all! - </para> - </section> - </chapter> - - -<!-- ****************************************************** --> -<!-- PCM Interface --> -<!-- ****************************************************** --> - <chapter id="pcm-interface"> - <title>PCM Interface</title> - - <section id="pcm-interface-general"> - <title>General</title> - <para> - The PCM middle layer of ALSA is quite powerful and it is only - necessary for each driver to implement the low-level functions - to access its hardware. - </para> - - <para> - For accessing to the PCM layer, you need to include - <filename><sound/pcm.h></filename> first. In addition, - <filename><sound/pcm_params.h></filename> might be needed - if you access to some functions related with hw_param. - </para> - - <para> - Each card device can have up to four pcm instances. A pcm - instance corresponds to a pcm device file. The limitation of - number of instances comes only from the available bit size of - the Linux's device numbers. Once when 64bit device number is - used, we'll have more pcm instances available. - </para> - - <para> - A pcm instance consists of pcm playback and capture streams, - and each pcm stream consists of one or more pcm substreams. Some - soundcards support multiple playback functions. For example, - emu10k1 has a PCM playback of 32 stereo substreams. In this case, at - each open, a free substream is (usually) automatically chosen - and opened. Meanwhile, when only one substream exists and it was - already opened, the successful open will either block - or error with <constant>EAGAIN</constant> according to the - file open mode. But you don't have to care about such details in your - driver. The PCM middle layer will take care of such work. - </para> - </section> - - <section id="pcm-interface-example"> - <title>Full Code Example</title> - <para> - The example code below does not include any hardware access - routines but shows only the skeleton, how to build up the PCM - interfaces. - - <example> - <title>PCM Example Code</title> - <programlisting> -<![CDATA[ - #include <sound/pcm.h> - .... - - /* hardware definition */ - static struct snd_pcm_hardware snd_mychip_playback_hw = { - .info = (SNDRV_PCM_INFO_MMAP | - SNDRV_PCM_INFO_INTERLEAVED | - SNDRV_PCM_INFO_BLOCK_TRANSFER | - SNDRV_PCM_INFO_MMAP_VALID), - .formats = SNDRV_PCM_FMTBIT_S16_LE, - .rates = SNDRV_PCM_RATE_8000_48000, - .rate_min = 8000, - .rate_max = 48000, - .channels_min = 2, - .channels_max = 2, - .buffer_bytes_max = 32768, - .period_bytes_min = 4096, - .period_bytes_max = 32768, - .periods_min = 1, - .periods_max = 1024, - }; - - /* hardware definition */ - static struct snd_pcm_hardware snd_mychip_capture_hw = { - .info = (SNDRV_PCM_INFO_MMAP | - SNDRV_PCM_INFO_INTERLEAVED | - SNDRV_PCM_INFO_BLOCK_TRANSFER | - SNDRV_PCM_INFO_MMAP_VALID), - .formats = SNDRV_PCM_FMTBIT_S16_LE, - .rates = SNDRV_PCM_RATE_8000_48000, - .rate_min = 8000, - .rate_max = 48000, - .channels_min = 2, - .channels_max = 2, - .buffer_bytes_max = 32768, - .period_bytes_min = 4096, - .period_bytes_max = 32768, - .periods_min = 1, - .periods_max = 1024, - }; - - /* open callback */ - static int snd_mychip_playback_open(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - struct snd_pcm_runtime *runtime = substream->runtime; - - runtime->hw = snd_mychip_playback_hw; - /* more hardware-initialization will be done here */ - .... - return 0; - } - - /* close callback */ - static int snd_mychip_playback_close(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - /* the hardware-specific codes will be here */ - .... - return 0; - - } - - /* open callback */ - static int snd_mychip_capture_open(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - struct snd_pcm_runtime *runtime = substream->runtime; - - runtime->hw = snd_mychip_capture_hw; - /* more hardware-initialization will be done here */ - .... - return 0; - } - - /* close callback */ - static int snd_mychip_capture_close(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - /* the hardware-specific codes will be here */ - .... - return 0; - - } - - /* hw_params callback */ - static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream, - struct snd_pcm_hw_params *hw_params) - { - return snd_pcm_lib_malloc_pages(substream, - params_buffer_bytes(hw_params)); - } - - /* hw_free callback */ - static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream) - { - return snd_pcm_lib_free_pages(substream); - } - - /* prepare callback */ - static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - struct snd_pcm_runtime *runtime = substream->runtime; - - /* set up the hardware with the current configuration - * for example... - */ - mychip_set_sample_format(chip, runtime->format); - mychip_set_sample_rate(chip, runtime->rate); - mychip_set_channels(chip, runtime->channels); - mychip_set_dma_setup(chip, runtime->dma_addr, - chip->buffer_size, - chip->period_size); - return 0; - } - - /* trigger callback */ - static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, - int cmd) - { - switch (cmd) { - case SNDRV_PCM_TRIGGER_START: - /* do something to start the PCM engine */ - .... - break; - case SNDRV_PCM_TRIGGER_STOP: - /* do something to stop the PCM engine */ - .... - break; - default: - return -EINVAL; - } - } - - /* pointer callback */ - static snd_pcm_uframes_t - snd_mychip_pcm_pointer(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - unsigned int current_ptr; - - /* get the current hardware pointer */ - current_ptr = mychip_get_hw_pointer(chip); - return current_ptr; - } - - /* operators */ - static struct snd_pcm_ops snd_mychip_playback_ops = { - .open = snd_mychip_playback_open, - .close = snd_mychip_playback_close, - .ioctl = snd_pcm_lib_ioctl, - .hw_params = snd_mychip_pcm_hw_params, - .hw_free = snd_mychip_pcm_hw_free, - .prepare = snd_mychip_pcm_prepare, - .trigger = snd_mychip_pcm_trigger, - .pointer = snd_mychip_pcm_pointer, - }; - - /* operators */ - static struct snd_pcm_ops snd_mychip_capture_ops = { - .open = snd_mychip_capture_open, - .close = snd_mychip_capture_close, - .ioctl = snd_pcm_lib_ioctl, - .hw_params = snd_mychip_pcm_hw_params, - .hw_free = snd_mychip_pcm_hw_free, - .prepare = snd_mychip_pcm_prepare, - .trigger = snd_mychip_pcm_trigger, - .pointer = snd_mychip_pcm_pointer, - }; - - /* - * definitions of capture are omitted here... - */ - - /* create a pcm device */ - static int snd_mychip_new_pcm(struct mychip *chip) - { - struct snd_pcm *pcm; - int err; - - err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); - if (err < 0) - return err; - pcm->private_data = chip; - strcpy(pcm->name, "My Chip"); - chip->pcm = pcm; - /* set operators */ - snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, - &snd_mychip_playback_ops); - snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, - &snd_mychip_capture_ops); - /* pre-allocation of buffers */ - /* NOTE: this may fail */ - snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, - snd_dma_pci_data(chip->pci), - 64*1024, 64*1024); - return 0; - } -]]> - </programlisting> - </example> - </para> - </section> - - <section id="pcm-interface-constructor"> - <title>Constructor</title> - <para> - A pcm instance is allocated by the <function>snd_pcm_new()</function> - function. It would be better to create a constructor for pcm, - namely, - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_mychip_new_pcm(struct mychip *chip) - { - struct snd_pcm *pcm; - int err; - - err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); - if (err < 0) - return err; - pcm->private_data = chip; - strcpy(pcm->name, "My Chip"); - chip->pcm = pcm; - .... - return 0; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The <function>snd_pcm_new()</function> function takes four - arguments. The first argument is the card pointer to which this - pcm is assigned, and the second is the ID string. - </para> - - <para> - The third argument (<parameter>index</parameter>, 0 in the - above) is the index of this new pcm. It begins from zero. If - you create more than one pcm instances, specify the - different numbers in this argument. For example, - <parameter>index</parameter> = 1 for the second PCM device. - </para> - - <para> - The fourth and fifth arguments are the number of substreams - for playback and capture, respectively. Here 1 is used for - both arguments. When no playback or capture substreams are available, - pass 0 to the corresponding argument. - </para> - - <para> - If a chip supports multiple playbacks or captures, you can - specify more numbers, but they must be handled properly in - open/close, etc. callbacks. When you need to know which - substream you are referring to, then it can be obtained from - struct <structname>snd_pcm_substream</structname> data passed to each callback - as follows: - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_pcm_substream *substream; - int index = substream->number; -]]> - </programlisting> - </informalexample> - </para> - - <para> - After the pcm is created, you need to set operators for each - pcm stream. - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, - &snd_mychip_playback_ops); - snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, - &snd_mychip_capture_ops); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The operators are defined typically like this: - - <informalexample> - <programlisting> -<![CDATA[ - static struct snd_pcm_ops snd_mychip_playback_ops = { - .open = snd_mychip_pcm_open, - .close = snd_mychip_pcm_close, - .ioctl = snd_pcm_lib_ioctl, - .hw_params = snd_mychip_pcm_hw_params, - .hw_free = snd_mychip_pcm_hw_free, - .prepare = snd_mychip_pcm_prepare, - .trigger = snd_mychip_pcm_trigger, - .pointer = snd_mychip_pcm_pointer, - }; -]]> - </programlisting> - </informalexample> - - All the callbacks are described in the - <link linkend="pcm-interface-operators"><citetitle> - Operators</citetitle></link> subsection. - </para> - - <para> - After setting the operators, you probably will want to - pre-allocate the buffer. For the pre-allocation, simply call - the following: - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, - snd_dma_pci_data(chip->pci), - 64*1024, 64*1024); -]]> - </programlisting> - </informalexample> - - It will allocate a buffer up to 64kB as default. - Buffer management details will be described in the later section <link - linkend="buffer-and-memory"><citetitle>Buffer and Memory - Management</citetitle></link>. - </para> - - <para> - Additionally, you can set some extra information for this pcm - in pcm->info_flags. - The available values are defined as - <constant>SNDRV_PCM_INFO_XXX</constant> in - <filename><sound/asound.h></filename>, which is used for - the hardware definition (described later). When your soundchip - supports only half-duplex, specify like this: - - <informalexample> - <programlisting> -<![CDATA[ - pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; -]]> - </programlisting> - </informalexample> - </para> - </section> - - <section id="pcm-interface-destructor"> - <title>... And the Destructor?</title> - <para> - The destructor for a pcm instance is not always - necessary. Since the pcm device will be released by the middle - layer code automatically, you don't have to call the destructor - explicitly. - </para> - - <para> - The destructor would be necessary if you created - special records internally and needed to release them. In such a - case, set the destructor function to - pcm->private_free: - - <example> - <title>PCM Instance with a Destructor</title> - <programlisting> -<![CDATA[ - static void mychip_pcm_free(struct snd_pcm *pcm) - { - struct mychip *chip = snd_pcm_chip(pcm); - /* free your own data */ - kfree(chip->my_private_pcm_data); - /* do what you like else */ - .... - } - - static int snd_mychip_new_pcm(struct mychip *chip) - { - struct snd_pcm *pcm; - .... - /* allocate your own data */ - chip->my_private_pcm_data = kmalloc(...); - /* set the destructor */ - pcm->private_data = chip; - pcm->private_free = mychip_pcm_free; - .... - } -]]> - </programlisting> - </example> - </para> - </section> - - <section id="pcm-interface-runtime"> - <title>Runtime Pointer - The Chest of PCM Information</title> - <para> - When the PCM substream is opened, a PCM runtime instance is - allocated and assigned to the substream. This pointer is - accessible via <constant>substream->runtime</constant>. - This runtime pointer holds most information you need - to control the PCM: the copy of hw_params and sw_params configurations, the buffer - pointers, mmap records, spinlocks, etc. - </para> - - <para> - The definition of runtime instance is found in - <filename><sound/pcm.h></filename>. Here are - the contents of this file: - <informalexample> - <programlisting> -<![CDATA[ -struct _snd_pcm_runtime { - /* -- Status -- */ - struct snd_pcm_substream *trigger_master; - snd_timestamp_t trigger_tstamp; /* trigger timestamp */ - int overrange; - snd_pcm_uframes_t avail_max; - snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ - snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/ - - /* -- HW params -- */ - snd_pcm_access_t access; /* access mode */ - snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */ - snd_pcm_subformat_t subformat; /* subformat */ - unsigned int rate; /* rate in Hz */ - unsigned int channels; /* channels */ - snd_pcm_uframes_t period_size; /* period size */ - unsigned int periods; /* periods */ - snd_pcm_uframes_t buffer_size; /* buffer size */ - unsigned int tick_time; /* tick time */ - snd_pcm_uframes_t min_align; /* Min alignment for the format */ - size_t byte_align; - unsigned int frame_bits; - unsigned int sample_bits; - unsigned int info; - unsigned int rate_num; - unsigned int rate_den; - - /* -- SW params -- */ - struct timespec tstamp_mode; /* mmap timestamp is updated */ - unsigned int period_step; - unsigned int sleep_min; /* min ticks to sleep */ - snd_pcm_uframes_t start_threshold; - snd_pcm_uframes_t stop_threshold; - snd_pcm_uframes_t silence_threshold; /* Silence filling happens when - noise is nearest than this */ - snd_pcm_uframes_t silence_size; /* Silence filling size */ - snd_pcm_uframes_t boundary; /* pointers wrap point */ - - snd_pcm_uframes_t silenced_start; - snd_pcm_uframes_t silenced_size; - - snd_pcm_sync_id_t sync; /* hardware synchronization ID */ - - /* -- mmap -- */ - volatile struct snd_pcm_mmap_status *status; - volatile struct snd_pcm_mmap_control *control; - atomic_t mmap_count; - - /* -- locking / scheduling -- */ - spinlock_t lock; - wait_queue_head_t sleep; - struct timer_list tick_timer; - struct fasync_struct *fasync; - - /* -- private section -- */ - void *private_data; - void (*private_free)(struct snd_pcm_runtime *runtime); - - /* -- hardware description -- */ - struct snd_pcm_hardware hw; - struct snd_pcm_hw_constraints hw_constraints; - - /* -- timer -- */ - unsigned int timer_resolution; /* timer resolution */ - - /* -- DMA -- */ - unsigned char *dma_area; /* DMA area */ - dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */ - size_t dma_bytes; /* size of DMA area */ - - struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */ - -#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE) - /* -- OSS things -- */ - struct snd_pcm_oss_runtime oss; -#endif -}; -]]> - </programlisting> - </informalexample> - </para> - - <para> - For the operators (callbacks) of each sound driver, most of - these records are supposed to be read-only. Only the PCM - middle-layer changes / updates them. The exceptions are - the hardware description (hw) DMA buffer information and the - private data. Besides, if you use the standard buffer allocation - method via <function>snd_pcm_lib_malloc_pages()</function>, - you don't need to set the DMA buffer information by yourself. - </para> - - <para> - In the sections below, important records are explained. - </para> - - <section id="pcm-interface-runtime-hw"> - <title>Hardware Description</title> - <para> - The hardware descriptor (struct <structname>snd_pcm_hardware</structname>) - contains the definitions of the fundamental hardware - configuration. Above all, you'll need to define this in - <link linkend="pcm-interface-operators-open-callback"><citetitle> - the open callback</citetitle></link>. - Note that the runtime instance holds the copy of the - descriptor, not the pointer to the existing descriptor. That - is, in the open callback, you can modify the copied descriptor - (<constant>runtime->hw</constant>) as you need. For example, if the maximum - number of channels is 1 only on some chip models, you can - still use the same hardware descriptor and change the - channels_max later: - <informalexample> - <programlisting> -<![CDATA[ - struct snd_pcm_runtime *runtime = substream->runtime; - ... - runtime->hw = snd_mychip_playback_hw; /* common definition */ - if (chip->model == VERY_OLD_ONE) - runtime->hw.channels_max = 1; -]]> - </programlisting> - </informalexample> - </para> - - <para> - Typically, you'll have a hardware descriptor as below: - <informalexample> - <programlisting> -<![CDATA[ - static struct snd_pcm_hardware snd_mychip_playback_hw = { - .info = (SNDRV_PCM_INFO_MMAP | - SNDRV_PCM_INFO_INTERLEAVED | - SNDRV_PCM_INFO_BLOCK_TRANSFER | - SNDRV_PCM_INFO_MMAP_VALID), - .formats = SNDRV_PCM_FMTBIT_S16_LE, - .rates = SNDRV_PCM_RATE_8000_48000, - .rate_min = 8000, - .rate_max = 48000, - .channels_min = 2, - .channels_max = 2, - .buffer_bytes_max = 32768, - .period_bytes_min = 4096, - .period_bytes_max = 32768, - .periods_min = 1, - .periods_max = 1024, - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - <itemizedlist> - <listitem><para> - The <structfield>info</structfield> field contains the type and - capabilities of this pcm. The bit flags are defined in - <filename><sound/asound.h></filename> as - <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you - have to specify whether the mmap is supported and which - interleaved format is supported. - When the hardware supports mmap, add the - <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the - hardware supports the interleaved or the non-interleaved - formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or - <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must - be set, respectively. If both are supported, you can set both, - too. - </para> - - <para> - In the above example, <constant>MMAP_VALID</constant> and - <constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap - mode. Usually both are set. Of course, - <constant>MMAP_VALID</constant> is set only if the mmap is - really supported. - </para> - - <para> - The other possible flags are - <constant>SNDRV_PCM_INFO_PAUSE</constant> and - <constant>SNDRV_PCM_INFO_RESUME</constant>. The - <constant>PAUSE</constant> bit means that the pcm supports the - <quote>pause</quote> operation, while the - <constant>RESUME</constant> bit means that the pcm supports - the full <quote>suspend/resume</quote> operation. - If the <constant>PAUSE</constant> flag is set, - the <structfield>trigger</structfield> callback below - must handle the corresponding (pause push/release) commands. - The suspend/resume trigger commands can be defined even without - the <constant>RESUME</constant> flag. See <link - linkend="power-management"><citetitle> - Power Management</citetitle></link> section for details. - </para> - - <para> - When the PCM substreams can be synchronized (typically, - synchronized start/stop of a playback and a capture streams), - you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>, - too. In this case, you'll need to check the linked-list of - PCM substreams in the trigger callback. This will be - described in the later section. - </para> - </listitem> - - <listitem> - <para> - <structfield>formats</structfield> field contains the bit-flags - of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>). - If the hardware supports more than one format, give all or'ed - bits. In the example above, the signed 16bit little-endian - format is specified. - </para> - </listitem> - - <listitem> - <para> - <structfield>rates</structfield> field contains the bit-flags of - supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>). - When the chip supports continuous rates, pass - <constant>CONTINUOUS</constant> bit additionally. - The pre-defined rate bits are provided only for typical - rates. If your chip supports unconventional rates, you need to add - the <constant>KNOT</constant> bit and set up the hardware - constraint manually (explained later). - </para> - </listitem> - - <listitem> - <para> - <structfield>rate_min</structfield> and - <structfield>rate_max</structfield> define the minimum and - maximum sample rate. This should correspond somehow to - <structfield>rates</structfield> bits. - </para> - </listitem> - - <listitem> - <para> - <structfield>channel_min</structfield> and - <structfield>channel_max</structfield> - define, as you might already expected, the minimum and maximum - number of channels. - </para> - </listitem> - - <listitem> - <para> - <structfield>buffer_bytes_max</structfield> defines the - maximum buffer size in bytes. There is no - <structfield>buffer_bytes_min</structfield> field, since - it can be calculated from the minimum period size and the - minimum number of periods. - Meanwhile, <structfield>period_bytes_min</structfield> and - define the minimum and maximum size of the period in bytes. - <structfield>periods_max</structfield> and - <structfield>periods_min</structfield> define the maximum and - minimum number of periods in the buffer. - </para> - - <para> - The <quote>period</quote> is a term that corresponds to - a fragment in the OSS world. The period defines the size at - which a PCM interrupt is generated. This size strongly - depends on the hardware. - Generally, the smaller period size will give you more - interrupts, that is, more controls. - In the case of capture, this size defines the input latency. - On the other hand, the whole buffer size defines the - output latency for the playback direction. - </para> - </listitem> - - <listitem> - <para> - There is also a field <structfield>fifo_size</structfield>. - This specifies the size of the hardware FIFO, but currently it - is neither used in the driver nor in the alsa-lib. So, you - can ignore this field. - </para> - </listitem> - </itemizedlist> - </para> - </section> - - <section id="pcm-interface-runtime-config"> - <title>PCM Configurations</title> - <para> - Ok, let's go back again to the PCM runtime records. - The most frequently referred records in the runtime instance are - the PCM configurations. - The PCM configurations are stored in the runtime instance - after the application sends <type>hw_params</type> data via - alsa-lib. There are many fields copied from hw_params and - sw_params structs. For example, - <structfield>format</structfield> holds the format type - chosen by the application. This field contains the enum value - <constant>SNDRV_PCM_FORMAT_XXX</constant>. - </para> - - <para> - One thing to be noted is that the configured buffer and period - sizes are stored in <quote>frames</quote> in the runtime. - In the ALSA world, 1 frame = channels * samples-size. - For conversion between frames and bytes, you can use the - <function>frames_to_bytes()</function> and - <function>bytes_to_frames()</function> helper functions. - <informalexample> - <programlisting> -<![CDATA[ - period_bytes = frames_to_bytes(runtime, runtime->period_size); -]]> - </programlisting> - </informalexample> - </para> - - <para> - Also, many software parameters (sw_params) are - stored in frames, too. Please check the type of the field. - <type>snd_pcm_uframes_t</type> is for the frames as unsigned - integer while <type>snd_pcm_sframes_t</type> is for the frames - as signed integer. - </para> - </section> - - <section id="pcm-interface-runtime-dma"> - <title>DMA Buffer Information</title> - <para> - The DMA buffer is defined by the following four fields, - <structfield>dma_area</structfield>, - <structfield>dma_addr</structfield>, - <structfield>dma_bytes</structfield> and - <structfield>dma_private</structfield>. - The <structfield>dma_area</structfield> holds the buffer - pointer (the logical address). You can call - <function>memcpy</function> from/to - this pointer. Meanwhile, <structfield>dma_addr</structfield> - holds the physical address of the buffer. This field is - specified only when the buffer is a linear buffer. - <structfield>dma_bytes</structfield> holds the size of buffer - in bytes. <structfield>dma_private</structfield> is used for - the ALSA DMA allocator. - </para> - - <para> - If you use a standard ALSA function, - <function>snd_pcm_lib_malloc_pages()</function>, for - allocating the buffer, these fields are set by the ALSA middle - layer, and you should <emphasis>not</emphasis> change them by - yourself. You can read them but not write them. - On the other hand, if you want to allocate the buffer by - yourself, you'll need to manage it in hw_params callback. - At least, <structfield>dma_bytes</structfield> is mandatory. - <structfield>dma_area</structfield> is necessary when the - buffer is mmapped. If your driver doesn't support mmap, this - field is not necessary. <structfield>dma_addr</structfield> - is also optional. You can use - <structfield>dma_private</structfield> as you like, too. - </para> - </section> - - <section id="pcm-interface-runtime-status"> - <title>Running Status</title> - <para> - The running status can be referred via <constant>runtime->status</constant>. - This is the pointer to the struct <structname>snd_pcm_mmap_status</structname> - record. For example, you can get the current DMA hardware - pointer via <constant>runtime->status->hw_ptr</constant>. - </para> - - <para> - The DMA application pointer can be referred via - <constant>runtime->control</constant>, which points to the - struct <structname>snd_pcm_mmap_control</structname> record. - However, accessing directly to this value is not recommended. - </para> - </section> - - <section id="pcm-interface-runtime-private"> - <title>Private Data</title> - <para> - You can allocate a record for the substream and store it in - <constant>runtime->private_data</constant>. Usually, this - is done in - <link linkend="pcm-interface-operators-open-callback"><citetitle> - the open callback</citetitle></link>. - Don't mix this with <constant>pcm->private_data</constant>. - The <constant>pcm->private_data</constant> usually points to the - chip instance assigned statically at the creation of PCM, while the - <constant>runtime->private_data</constant> points to a dynamic - data structure created at the PCM open callback. - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_open(struct snd_pcm_substream *substream) - { - struct my_pcm_data *data; - .... - data = kmalloc(sizeof(*data), GFP_KERNEL); - substream->runtime->private_data = data; - .... - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The allocated object must be released in - <link linkend="pcm-interface-operators-open-callback"><citetitle> - the close callback</citetitle></link>. - </para> - </section> - - </section> - - <section id="pcm-interface-operators"> - <title>Operators</title> - <para> - OK, now let me give details about each pcm callback - (<parameter>ops</parameter>). In general, every callback must - return 0 if successful, or a negative error number - such as <constant>-EINVAL</constant>. To choose an appropriate - error number, it is advised to check what value other parts of - the kernel return when the same kind of request fails. - </para> - - <para> - The callback function takes at least the argument with - <structname>snd_pcm_substream</structname> pointer. To retrieve - the chip record from the given substream instance, you can use the - following macro. - - <informalexample> - <programlisting> -<![CDATA[ - int xxx() { - struct mychip *chip = snd_pcm_substream_chip(substream); - .... - } -]]> - </programlisting> - </informalexample> - - The macro reads <constant>substream->private_data</constant>, - which is a copy of <constant>pcm->private_data</constant>. - You can override the former if you need to assign different data - records per PCM substream. For example, the cmi8330 driver assigns - different private_data for playback and capture directions, - because it uses two different codecs (SB- and AD-compatible) for - different directions. - </para> - - <section id="pcm-interface-operators-open-callback"> - <title>open callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_open(struct snd_pcm_substream *substream); -]]> - </programlisting> - </informalexample> - - This is called when a pcm substream is opened. - </para> - - <para> - At least, here you have to initialize the runtime->hw - record. Typically, this is done by like this: - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_open(struct snd_pcm_substream *substream) - { - struct mychip *chip = snd_pcm_substream_chip(substream); - struct snd_pcm_runtime *runtime = substream->runtime; - - runtime->hw = snd_mychip_playback_hw; - return 0; - } -]]> - </programlisting> - </informalexample> - - where <parameter>snd_mychip_playback_hw</parameter> is the - pre-defined hardware description. - </para> - - <para> - You can allocate a private data in this callback, as described - in <link linkend="pcm-interface-runtime-private"><citetitle> - Private Data</citetitle></link> section. - </para> - - <para> - If the hardware configuration needs more constraints, set the - hardware constraints here, too. - See <link linkend="pcm-interface-constraints"><citetitle> - Constraints</citetitle></link> for more details. - </para> - </section> - - <section id="pcm-interface-operators-close-callback"> - <title>close callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_close(struct snd_pcm_substream *substream); -]]> - </programlisting> - </informalexample> - - Obviously, this is called when a pcm substream is closed. - </para> - - <para> - Any private instance for a pcm substream allocated in the - open callback will be released here. - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_close(struct snd_pcm_substream *substream) - { - .... - kfree(substream->runtime->private_data); - .... - } -]]> - </programlisting> - </informalexample> - </para> - </section> - - <section id="pcm-interface-operators-ioctl-callback"> - <title>ioctl callback</title> - <para> - This is used for any special call to pcm ioctls. But - usually you can pass a generic ioctl callback, - <function>snd_pcm_lib_ioctl</function>. - </para> - </section> - - <section id="pcm-interface-operators-hw-params-callback"> - <title>hw_params callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_hw_params(struct snd_pcm_substream *substream, - struct snd_pcm_hw_params *hw_params); -]]> - </programlisting> - </informalexample> - </para> - - <para> - This is called when the hardware parameter - (<structfield>hw_params</structfield>) is set - up by the application, - that is, once when the buffer size, the period size, the - format, etc. are defined for the pcm substream. - </para> - - <para> - Many hardware setups should be done in this callback, - including the allocation of buffers. - </para> - - <para> - Parameters to be initialized are retrieved by - <function>params_xxx()</function> macros. To allocate - buffer, you can call a helper function, - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params)); -]]> - </programlisting> - </informalexample> - - <function>snd_pcm_lib_malloc_pages()</function> is available - only when the DMA buffers have been pre-allocated. - See the section <link - linkend="buffer-and-memory-buffer-types"><citetitle> - Buffer Types</citetitle></link> for more details. - </para> - - <para> - Note that this and <structfield>prepare</structfield> callbacks - may be called multiple times per initialization. - For example, the OSS emulation may - call these callbacks at each change via its ioctl. - </para> - - <para> - Thus, you need to be careful not to allocate the same buffers - many times, which will lead to memory leaks! Calling the - helper function above many times is OK. It will release the - previous buffer automatically when it was already allocated. - </para> - - <para> - Another note is that this callback is non-atomic - (schedulable) as default, i.e. when no - <structfield>nonatomic</structfield> flag set. - This is important, because the - <structfield>trigger</structfield> callback - is atomic (non-schedulable). That is, mutexes or any - schedule-related functions are not available in - <structfield>trigger</structfield> callback. - Please see the subsection - <link linkend="pcm-interface-atomicity"><citetitle> - Atomicity</citetitle></link> for details. - </para> - </section> - - <section id="pcm-interface-operators-hw-free-callback"> - <title>hw_free callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_hw_free(struct snd_pcm_substream *substream); -]]> - </programlisting> - </informalexample> - </para> - - <para> - This is called to release the resources allocated via - <structfield>hw_params</structfield>. For example, releasing the - buffer via - <function>snd_pcm_lib_malloc_pages()</function> is done by - calling the following: - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_lib_free_pages(substream); -]]> - </programlisting> - </informalexample> - </para> - - <para> - This function is always called before the close callback is called. - Also, the callback may be called multiple times, too. - Keep track whether the resource was already released. - </para> - </section> - - <section id="pcm-interface-operators-prepare-callback"> - <title>prepare callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_prepare(struct snd_pcm_substream *substream); -]]> - </programlisting> - </informalexample> - </para> - - <para> - This callback is called when the pcm is - <quote>prepared</quote>. You can set the format type, sample - rate, etc. here. The difference from - <structfield>hw_params</structfield> is that the - <structfield>prepare</structfield> callback will be called each - time - <function>snd_pcm_prepare()</function> is called, i.e. when - recovering after underruns, etc. - </para> - - <para> - Note that this callback is now non-atomic. - You can use schedule-related functions safely in this callback. - </para> - - <para> - In this and the following callbacks, you can refer to the - values via the runtime record, - substream->runtime. - For example, to get the current - rate, format or channels, access to - runtime->rate, - runtime->format or - runtime->channels, respectively. - The physical address of the allocated buffer is set to - runtime->dma_area. The buffer and period sizes are - in runtime->buffer_size and runtime->period_size, - respectively. - </para> - - <para> - Be careful that this callback will be called many times at - each setup, too. - </para> - </section> - - <section id="pcm-interface-operators-trigger-callback"> - <title>trigger callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd); -]]> - </programlisting> - </informalexample> - - This is called when the pcm is started, stopped or paused. - </para> - - <para> - Which action is specified in the second argument, - <constant>SNDRV_PCM_TRIGGER_XXX</constant> in - <filename><sound/pcm.h></filename>. At least, - the <constant>START</constant> and <constant>STOP</constant> - commands must be defined in this callback. - - <informalexample> - <programlisting> -<![CDATA[ - switch (cmd) { - case SNDRV_PCM_TRIGGER_START: - /* do something to start the PCM engine */ - break; - case SNDRV_PCM_TRIGGER_STOP: - /* do something to stop the PCM engine */ - break; - default: - return -EINVAL; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - When the pcm supports the pause operation (given in the info - field of the hardware table), the <constant>PAUSE_PUSH</constant> - and <constant>PAUSE_RELEASE</constant> commands must be - handled here, too. The former is the command to pause the pcm, - and the latter to restart the pcm again. - </para> - - <para> - When the pcm supports the suspend/resume operation, - regardless of full or partial suspend/resume support, - the <constant>SUSPEND</constant> and <constant>RESUME</constant> - commands must be handled, too. - These commands are issued when the power-management status is - changed. Obviously, the <constant>SUSPEND</constant> and - <constant>RESUME</constant> commands - suspend and resume the pcm substream, and usually, they - are identical to the <constant>STOP</constant> and - <constant>START</constant> commands, respectively. - See the <link linkend="power-management"><citetitle> - Power Management</citetitle></link> section for details. - </para> - - <para> - As mentioned, this callback is atomic as default unless - <structfield>nonatomic</structfield> flag set, and - you cannot call functions which may sleep. - The trigger callback should be as minimal as possible, - just really triggering the DMA. The other stuff should be - initialized hw_params and prepare callbacks properly - beforehand. - </para> - </section> - - <section id="pcm-interface-operators-pointer-callback"> - <title>pointer callback</title> - <para> - <informalexample> - <programlisting> -<![CDATA[ - static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream) -]]> - </programlisting> - </informalexample> - - This callback is called when the PCM middle layer inquires - the current hardware position on the buffer. The position must - be returned in frames, - ranging from 0 to buffer_size - 1. - </para> - - <para> - This is called usually from the buffer-update routine in the - pcm middle layer, which is invoked when - <function>snd_pcm_period_elapsed()</function> is called in the - interrupt routine. Then the pcm middle layer updates the - position and calculates the available space, and wakes up the - sleeping poll threads, etc. - </para> - - <para> - This callback is also atomic as default. - </para> - </section> - - <section id="pcm-interface-operators-copy-silence"> - <title>copy and silence callbacks</title> - <para> - These callbacks are not mandatory, and can be omitted in - most cases. These callbacks are used when the hardware buffer - cannot be in the normal memory space. Some chips have their - own buffer on the hardware which is not mappable. In such a - case, you have to transfer the data manually from the memory - buffer to the hardware buffer. Or, if the buffer is - non-contiguous on both physical and virtual memory spaces, - these callbacks must be defined, too. - </para> - - <para> - If these two callbacks are defined, copy and set-silence - operations are done by them. The detailed will be described in - the later section <link - linkend="buffer-and-memory"><citetitle>Buffer and Memory - Management</citetitle></link>. - </para> - </section> - - <section id="pcm-interface-operators-ack"> - <title>ack callback</title> - <para> - This callback is also not mandatory. This callback is called - when the appl_ptr is updated in read or write operations. - Some drivers like emu10k1-fx and cs46xx need to track the - current appl_ptr for the internal buffer, and this callback - is useful only for such a purpose. - </para> - <para> - This callback is atomic as default. - </para> - </section> - - <section id="pcm-interface-operators-page-callback"> - <title>page callback</title> - - <para> - This callback is optional too. This callback is used - mainly for non-contiguous buffers. The mmap calls this - callback to get the page address. Some examples will be - explained in the later section <link - linkend="buffer-and-memory"><citetitle>Buffer and Memory - Management</citetitle></link>, too. - </para> - </section> - </section> - - <section id="pcm-interface-interrupt-handler"> - <title>Interrupt Handler</title> - <para> - The rest of pcm stuff is the PCM interrupt handler. The - role of PCM interrupt handler in the sound driver is to update - the buffer position and to tell the PCM middle layer when the - buffer position goes across the prescribed period size. To - inform this, call the <function>snd_pcm_period_elapsed()</function> - function. - </para> - - <para> - There are several types of sound chips to generate the interrupts. - </para> - - <section id="pcm-interface-interrupt-handler-boundary"> - <title>Interrupts at the period (fragment) boundary</title> - <para> - This is the most frequently found type: the hardware - generates an interrupt at each period boundary. - In this case, you can call - <function>snd_pcm_period_elapsed()</function> at each - interrupt. - </para> - - <para> - <function>snd_pcm_period_elapsed()</function> takes the - substream pointer as its argument. Thus, you need to keep the - substream pointer accessible from the chip instance. For - example, define substream field in the chip record to hold the - current running substream pointer, and set the pointer value - at open callback (and reset at close callback). - </para> - - <para> - If you acquire a spinlock in the interrupt handler, and the - lock is used in other pcm callbacks, too, then you have to - release the lock before calling - <function>snd_pcm_period_elapsed()</function>, because - <function>snd_pcm_period_elapsed()</function> calls other pcm - callbacks inside. - </para> - - <para> - Typical code would be like: - - <example> - <title>Interrupt Handler Case #1</title> - <programlisting> -<![CDATA[ - static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) - { - struct mychip *chip = dev_id; - spin_lock(&chip->lock); - .... - if (pcm_irq_invoked(chip)) { - /* call updater, unlock before it */ - spin_unlock(&chip->lock); - snd_pcm_period_elapsed(chip->substream); - spin_lock(&chip->lock); - /* acknowledge the interrupt if necessary */ - } - .... - spin_unlock(&chip->lock); - return IRQ_HANDLED; - } -]]> - </programlisting> - </example> - </para> - </section> - - <section id="pcm-interface-interrupt-handler-timer"> - <title>High frequency timer interrupts</title> - <para> - This happens when the hardware doesn't generate interrupts - at the period boundary but issues timer interrupts at a fixed - timer rate (e.g. es1968 or ymfpci drivers). - In this case, you need to check the current hardware - position and accumulate the processed sample length at each - interrupt. When the accumulated size exceeds the period - size, call - <function>snd_pcm_period_elapsed()</function> and reset the - accumulator. - </para> - - <para> - Typical code would be like the following. - - <example> - <title>Interrupt Handler Case #2</title> - <programlisting> -<![CDATA[ - static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) - { - struct mychip *chip = dev_id; - spin_lock(&chip->lock); - .... - if (pcm_irq_invoked(chip)) { - unsigned int last_ptr, size; - /* get the current hardware pointer (in frames) */ - last_ptr = get_hw_ptr(chip); - /* calculate the processed frames since the - * last update - */ - if (last_ptr < chip->last_ptr) - size = runtime->buffer_size + last_ptr - - chip->last_ptr; - else - size = last_ptr - chip->last_ptr; - /* remember the last updated point */ - chip->last_ptr = last_ptr; - /* accumulate the size */ - chip->size += size; - /* over the period boundary? */ - if (chip->size >= runtime->period_size) { - /* reset the accumulator */ - chip->size %= runtime->period_size; - /* call updater */ - spin_unlock(&chip->lock); - snd_pcm_period_elapsed(substream); - spin_lock(&chip->lock); - } - /* acknowledge the interrupt if necessary */ - } - .... - spin_unlock(&chip->lock); - return IRQ_HANDLED; - } -]]> - </programlisting> - </example> - </para> - </section> - - <section id="pcm-interface-interrupt-handler-both"> - <title>On calling <function>snd_pcm_period_elapsed()</function></title> - <para> - In both cases, even if more than one period are elapsed, you - don't have to call - <function>snd_pcm_period_elapsed()</function> many times. Call - only once. And the pcm layer will check the current hardware - pointer and update to the latest status. - </para> - </section> - </section> - - <section id="pcm-interface-atomicity"> - <title>Atomicity</title> - <para> - One of the most important (and thus difficult to debug) problems - in kernel programming are race conditions. - In the Linux kernel, they are usually avoided via spin-locks, mutexes - or semaphores. In general, if a race condition can happen - in an interrupt handler, it has to be managed atomically, and you - have to use a spinlock to protect the critical session. If the - critical section is not in interrupt handler code and - if taking a relatively long time to execute is acceptable, you - should use mutexes or semaphores instead. - </para> - - <para> - As already seen, some pcm callbacks are atomic and some are - not. For example, the <parameter>hw_params</parameter> callback is - non-atomic, while <parameter>trigger</parameter> callback is - atomic. This means, the latter is called already in a spinlock - held by the PCM middle layer. Please take this atomicity into - account when you choose a locking scheme in the callbacks. - </para> - - <para> - In the atomic callbacks, you cannot use functions which may call - <function>schedule</function> or go to - <function>sleep</function>. Semaphores and mutexes can sleep, - and hence they cannot be used inside the atomic callbacks - (e.g. <parameter>trigger</parameter> callback). - To implement some delay in such a callback, please use - <function>udelay()</function> or <function>mdelay()</function>. - </para> - - <para> - All three atomic callbacks (trigger, pointer, and ack) are - called with local interrupts disabled. - </para> - - <para> - The recent changes in PCM core code, however, allow all PCM - operations to be non-atomic. This assumes that the all caller - sides are in non-atomic contexts. For example, the function - <function>snd_pcm_period_elapsed()</function> is called - typically from the interrupt handler. But, if you set up the - driver to use a threaded interrupt handler, this call can be in - non-atomic context, too. In such a case, you can set - <structfield>nonatomic</structfield> filed of - <structname>snd_pcm</structname> object after creating it. - When this flag is set, mutex and rwsem are used internally in - the PCM core instead of spin and rwlocks, so that you can call - all PCM functions safely in a non-atomic context. - </para> - - </section> - <section id="pcm-interface-constraints"> - <title>Constraints</title> - <para> - If your chip supports unconventional sample rates, or only the - limited samples, you need to set a constraint for the - condition. - </para> - - <para> - For example, in order to restrict the sample rates in the some - supported values, use - <function>snd_pcm_hw_constraint_list()</function>. - You need to call this function in the open callback. - - <example> - <title>Example of Hardware Constraints</title> - <programlisting> -<![CDATA[ - static unsigned int rates[] = - {4000, 10000, 22050, 44100}; - static struct snd_pcm_hw_constraint_list constraints_rates = { - .count = ARRAY_SIZE(rates), - .list = rates, - .mask = 0, - }; - - static int snd_mychip_pcm_open(struct snd_pcm_substream *substream) - { - int err; - .... - err = snd_pcm_hw_constraint_list(substream->runtime, 0, - SNDRV_PCM_HW_PARAM_RATE, - &constraints_rates); - if (err < 0) - return err; - .... - } -]]> - </programlisting> - </example> - </para> - - <para> - There are many different constraints. - Look at <filename>sound/pcm.h</filename> for a complete list. - You can even define your own constraint rules. - For example, let's suppose my_chip can manage a substream of 1 channel - if and only if the format is S16_LE, otherwise it supports any format - specified in the <structname>snd_pcm_hardware</structname> structure (or in any - other constraint_list). You can build a rule like this: - - <example> - <title>Example of Hardware Constraints for Channels</title> - <programlisting> -<![CDATA[ - static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, - struct snd_pcm_hw_rule *rule) - { - struct snd_interval *c = hw_param_interval(params, - SNDRV_PCM_HW_PARAM_CHANNELS); - struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); - struct snd_interval ch; - - snd_interval_any(&ch); - if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { - ch.min = ch.max = 1; - ch.integer = 1; - return snd_interval_refine(c, &ch); - } - return 0; - } -]]> - </programlisting> - </example> - </para> - - <para> - Then you need to call this function to add your rule: - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, - hw_rule_channels_by_format, NULL, - SNDRV_PCM_HW_PARAM_FORMAT, -1); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The rule function is called when an application sets the PCM - format, and it refines the number of channels accordingly. - But an application may set the number of channels before - setting the format. Thus you also need to define the inverse rule: - - <example> - <title>Example of Hardware Constraints for Formats</title> - <programlisting> -<![CDATA[ - static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, - struct snd_pcm_hw_rule *rule) - { - struct snd_interval *c = hw_param_interval(params, - SNDRV_PCM_HW_PARAM_CHANNELS); - struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); - struct snd_mask fmt; - - snd_mask_any(&fmt); /* Init the struct */ - if (c->min < 2) { - fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; - return snd_mask_refine(f, &fmt); - } - return 0; - } -]]> - </programlisting> - </example> - </para> - - <para> - ...and in the open callback: - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, - hw_rule_format_by_channels, NULL, - SNDRV_PCM_HW_PARAM_CHANNELS, -1); -]]> - </programlisting> - </informalexample> - </para> - - <para> - I won't give more details here, rather I - would like to say, <quote>Luke, use the source.</quote> - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Control Interface --> -<!-- ****************************************************** --> - <chapter id="control-interface"> - <title>Control Interface</title> - - <section id="control-interface-general"> - <title>General</title> - <para> - The control interface is used widely for many switches, - sliders, etc. which are accessed from user-space. Its most - important use is the mixer interface. In other words, since ALSA - 0.9.x, all the mixer stuff is implemented on the control kernel API. - </para> - - <para> - ALSA has a well-defined AC97 control module. If your chip - supports only the AC97 and nothing else, you can skip this - section. - </para> - - <para> - The control API is defined in - <filename><sound/control.h></filename>. - Include this file if you want to add your own controls. - </para> - </section> - - <section id="control-interface-definition"> - <title>Definition of Controls</title> - <para> - To create a new control, you need to define the - following three - callbacks: <structfield>info</structfield>, - <structfield>get</structfield> and - <structfield>put</structfield>. Then, define a - struct <structname>snd_kcontrol_new</structname> record, such as: - - <example> - <title>Definition of a Control</title> - <programlisting> -<![CDATA[ - static struct snd_kcontrol_new my_control = { - .iface = SNDRV_CTL_ELEM_IFACE_MIXER, - .name = "PCM Playback Switch", - .index = 0, - .access = SNDRV_CTL_ELEM_ACCESS_READWRITE, - .private_value = 0xffff, - .info = my_control_info, - .get = my_control_get, - .put = my_control_put - }; -]]> - </programlisting> - </example> - </para> - - <para> - The <structfield>iface</structfield> field specifies the control - type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which - is usually <constant>MIXER</constant>. - Use <constant>CARD</constant> for global controls that are not - logically part of the mixer. - If the control is closely associated with some specific device on - the sound card, use <constant>HWDEP</constant>, - <constant>PCM</constant>, <constant>RAWMIDI</constant>, - <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and - specify the device number with the - <structfield>device</structfield> and - <structfield>subdevice</structfield> fields. - </para> - - <para> - The <structfield>name</structfield> is the name identifier - string. Since ALSA 0.9.x, the control name is very important, - because its role is classified from its name. There are - pre-defined standard control names. The details are described in - the <link linkend="control-interface-control-names"><citetitle> - Control Names</citetitle></link> subsection. - </para> - - <para> - The <structfield>index</structfield> field holds the index number - of this control. If there are several different controls with - the same name, they can be distinguished by the index - number. This is the case when - several codecs exist on the card. If the index is zero, you can - omit the definition above. - </para> - - <para> - The <structfield>access</structfield> field contains the access - type of this control. Give the combination of bit masks, - <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there. - The details will be explained in - the <link linkend="control-interface-access-flags"><citetitle> - Access Flags</citetitle></link> subsection. - </para> - - <para> - The <structfield>private_value</structfield> field contains - an arbitrary long integer value for this record. When using - the generic <structfield>info</structfield>, - <structfield>get</structfield> and - <structfield>put</structfield> callbacks, you can pass a value - through this field. If several small numbers are necessary, you can - combine them in bitwise. Or, it's possible to give a pointer - (casted to unsigned long) of some record to this field, too. - </para> - - <para> - The <structfield>tlv</structfield> field can be used to provide - metadata about the control; see the - <link linkend="control-interface-tlv"> - <citetitle>Metadata</citetitle></link> subsection. - </para> - - <para> - The other three are - <link linkend="control-interface-callbacks"><citetitle> - callback functions</citetitle></link>. - </para> - </section> - - <section id="control-interface-control-names"> - <title>Control Names</title> - <para> - There are some standards to define the control names. A - control is usually defined from the three parts as - <quote>SOURCE DIRECTION FUNCTION</quote>. - </para> - - <para> - The first, <constant>SOURCE</constant>, specifies the source - of the control, and is a string such as <quote>Master</quote>, - <quote>PCM</quote>, <quote>CD</quote> and - <quote>Line</quote>. There are many pre-defined sources. - </para> - - <para> - The second, <constant>DIRECTION</constant>, is one of the - following strings according to the direction of the control: - <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass - Playback</quote> and <quote>Bypass Capture</quote>. Or, it can - be omitted, meaning both playback and capture directions. - </para> - - <para> - The third, <constant>FUNCTION</constant>, is one of the - following strings according to the function of the control: - <quote>Switch</quote>, <quote>Volume</quote> and - <quote>Route</quote>. - </para> - - <para> - The example of control names are, thus, <quote>Master Capture - Switch</quote> or <quote>PCM Playback Volume</quote>. - </para> - - <para> - There are some exceptions: - </para> - - <section id="control-interface-control-names-global"> - <title>Global capture and playback</title> - <para> - <quote>Capture Source</quote>, <quote>Capture Switch</quote> - and <quote>Capture Volume</quote> are used for the global - capture (input) source, switch and volume. Similarly, - <quote>Playback Switch</quote> and <quote>Playback - Volume</quote> are used for the global output gain switch and - volume. - </para> - </section> - - <section id="control-interface-control-names-tone"> - <title>Tone-controls</title> - <para> - tone-control switch and volumes are specified like - <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control - - Switch</quote>, <quote>Tone Control - Bass</quote>, - <quote>Tone Control - Center</quote>. - </para> - </section> - - <section id="control-interface-control-names-3d"> - <title>3D controls</title> - <para> - 3D-control switches and volumes are specified like <quote>3D - Control - XXX</quote>, e.g. <quote>3D Control - - Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D - Control - Space</quote>. - </para> - </section> - - <section id="control-interface-control-names-mic"> - <title>Mic boost</title> - <para> - Mic-boost switch is set as <quote>Mic Boost</quote> or - <quote>Mic Boost (6dB)</quote>. - </para> - - <para> - More precise information can be found in - <filename>Documentation/sound/alsa/ControlNames.txt</filename>. - </para> - </section> - </section> - - <section id="control-interface-access-flags"> - <title>Access Flags</title> - - <para> - The access flag is the bitmask which specifies the access type - of the given control. The default access type is - <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>, - which means both read and write are allowed to this control. - When the access flag is omitted (i.e. = 0), it is - considered as <constant>READWRITE</constant> access as default. - </para> - - <para> - When the control is read-only, pass - <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead. - In this case, you don't have to define - the <structfield>put</structfield> callback. - Similarly, when the control is write-only (although it's a rare - case), you can use the <constant>WRITE</constant> flag instead, and - you don't need the <structfield>get</structfield> callback. - </para> - - <para> - If the control value changes frequently (e.g. the VU meter), - <constant>VOLATILE</constant> flag should be given. This means - that the control may be changed without - <link linkend="control-interface-change-notification"><citetitle> - notification</citetitle></link>. Applications should poll such - a control constantly. - </para> - - <para> - When the control is inactive, set - the <constant>INACTIVE</constant> flag, too. - There are <constant>LOCK</constant> and - <constant>OWNER</constant> flags to change the write - permissions. - </para> - - </section> - - <section id="control-interface-callbacks"> - <title>Callbacks</title> - - <section id="control-interface-callbacks-info"> - <title>info callback</title> - <para> - The <structfield>info</structfield> callback is used to get - detailed information on this control. This must store the - values of the given struct <structname>snd_ctl_elem_info</structname> - object. For example, for a boolean control with a single - element: - - <example> - <title>Example of info callback</title> - <programlisting> -<![CDATA[ - static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_info *uinfo) - { - uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; - uinfo->count = 1; - uinfo->value.integer.min = 0; - uinfo->value.integer.max = 1; - return 0; - } -]]> - </programlisting> - </example> - </para> - - <para> - The <structfield>type</structfield> field specifies the type - of the control. There are <constant>BOOLEAN</constant>, - <constant>INTEGER</constant>, <constant>ENUMERATED</constant>, - <constant>BYTES</constant>, <constant>IEC958</constant> and - <constant>INTEGER64</constant>. The - <structfield>count</structfield> field specifies the - number of elements in this control. For example, a stereo - volume would have count = 2. The - <structfield>value</structfield> field is a union, and - the values stored are depending on the type. The boolean and - integer types are identical. - </para> - - <para> - The enumerated type is a bit different from others. You'll - need to set the string for the currently given item index. - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_info *uinfo) - { - static char *texts[4] = { - "First", "Second", "Third", "Fourth" - }; - uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED; - uinfo->count = 1; - uinfo->value.enumerated.items = 4; - if (uinfo->value.enumerated.item > 3) - uinfo->value.enumerated.item = 3; - strcpy(uinfo->value.enumerated.name, - texts[uinfo->value.enumerated.item]); - return 0; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The above callback can be simplified with a helper function, - <function>snd_ctl_enum_info</function>. The final code - looks like below. - (You can pass ARRAY_SIZE(texts) instead of 4 in the third - argument; it's a matter of taste.) - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_info *uinfo) - { - static char *texts[4] = { - "First", "Second", "Third", "Fourth" - }; - return snd_ctl_enum_info(uinfo, 1, 4, texts); - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - Some common info callbacks are available for your convenience: - <function>snd_ctl_boolean_mono_info()</function> and - <function>snd_ctl_boolean_stereo_info()</function>. - Obviously, the former is an info callback for a mono channel - boolean item, just like <function>snd_myctl_mono_info</function> - above, and the latter is for a stereo channel boolean item. - </para> - - </section> - - <section id="control-interface-callbacks-get"> - <title>get callback</title> - - <para> - This callback is used to read the current value of the - control and to return to user-space. - </para> - - <para> - For example, - - <example> - <title>Example of get callback</title> - <programlisting> -<![CDATA[ - static int snd_myctl_get(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_value *ucontrol) - { - struct mychip *chip = snd_kcontrol_chip(kcontrol); - ucontrol->value.integer.value[0] = get_some_value(chip); - return 0; - } -]]> - </programlisting> - </example> - </para> - - <para> - The <structfield>value</structfield> field depends on - the type of control as well as on the info callback. For example, - the sb driver uses this field to store the register offset, - the bit-shift and the bit-mask. The - <structfield>private_value</structfield> field is set as follows: - <informalexample> - <programlisting> -<![CDATA[ - .private_value = reg | (shift << 16) | (mask << 24) -]]> - </programlisting> - </informalexample> - and is retrieved in callbacks like - <informalexample> - <programlisting> -<![CDATA[ - static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_value *ucontrol) - { - int reg = kcontrol->private_value & 0xff; - int shift = (kcontrol->private_value >> 16) & 0xff; - int mask = (kcontrol->private_value >> 24) & 0xff; - .... - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - In the <structfield>get</structfield> callback, - you have to fill all the elements if the - control has more than one elements, - i.e. <structfield>count</structfield> > 1. - In the example above, we filled only one element - (<structfield>value.integer.value[0]</structfield>) since it's - assumed as <structfield>count</structfield> = 1. - </para> - </section> - - <section id="control-interface-callbacks-put"> - <title>put callback</title> - - <para> - This callback is used to write a value from user-space. - </para> - - <para> - For example, - - <example> - <title>Example of put callback</title> - <programlisting> -<![CDATA[ - static int snd_myctl_put(struct snd_kcontrol *kcontrol, - struct snd_ctl_elem_value *ucontrol) - { - struct mychip *chip = snd_kcontrol_chip(kcontrol); - int changed = 0; - if (chip->current_value != - ucontrol->value.integer.value[0]) { - change_current_value(chip, - ucontrol->value.integer.value[0]); - changed = 1; - } - return changed; - } -]]> - </programlisting> - </example> - - As seen above, you have to return 1 if the value is - changed. If the value is not changed, return 0 instead. - If any fatal error happens, return a negative error code as - usual. - </para> - - <para> - As in the <structfield>get</structfield> callback, - when the control has more than one elements, - all elements must be evaluated in this callback, too. - </para> - </section> - - <section id="control-interface-callbacks-all"> - <title>Callbacks are not atomic</title> - <para> - All these three callbacks are basically not atomic. - </para> - </section> - </section> - - <section id="control-interface-constructor"> - <title>Constructor</title> - <para> - When everything is ready, finally we can create a new - control. To create a control, there are two functions to be - called, <function>snd_ctl_new1()</function> and - <function>snd_ctl_add()</function>. - </para> - - <para> - In the simplest way, you can do like this: - - <informalexample> - <programlisting> -<![CDATA[ - err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip)); - if (err < 0) - return err; -]]> - </programlisting> - </informalexample> - - where <parameter>my_control</parameter> is the - struct <structname>snd_kcontrol_new</structname> object defined above, and chip - is the object pointer to be passed to - kcontrol->private_data - which can be referred to in callbacks. - </para> - - <para> - <function>snd_ctl_new1()</function> allocates a new - <structname>snd_kcontrol</structname> instance, - and <function>snd_ctl_add</function> assigns the given - control component to the card. - </para> - </section> - - <section id="control-interface-change-notification"> - <title>Change Notification</title> - <para> - If you need to change and update a control in the interrupt - routine, you can call <function>snd_ctl_notify()</function>. For - example, - - <informalexample> - <programlisting> -<![CDATA[ - snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer); -]]> - </programlisting> - </informalexample> - - This function takes the card pointer, the event-mask, and the - control id pointer for the notification. The event-mask - specifies the types of notification, for example, in the above - example, the change of control values is notified. - The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname> - to be notified. - You can find some examples in <filename>es1938.c</filename> or - <filename>es1968.c</filename> for hardware volume interrupts. - </para> - </section> - - <section id="control-interface-tlv"> - <title>Metadata</title> - <para> - To provide information about the dB values of a mixer control, use - on of the <constant>DECLARE_TLV_xxx</constant> macros from - <filename><sound/tlv.h></filename> to define a variable - containing this information, set the<structfield>tlv.p - </structfield> field to point to this variable, and include the - <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the - <structfield>access</structfield> field; like this: - <informalexample> - <programlisting> -<![CDATA[ - static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0); - - static struct snd_kcontrol_new my_control = { - ... - .access = SNDRV_CTL_ELEM_ACCESS_READWRITE | - SNDRV_CTL_ELEM_ACCESS_TLV_READ, - ... - .tlv.p = db_scale_my_control, - }; -]]> - </programlisting> - </informalexample> - </para> - - <para> - The <function>DECLARE_TLV_DB_SCALE</function> macro defines - information about a mixer control where each step in the control's - value changes the dB value by a constant dB amount. - The first parameter is the name of the variable to be defined. - The second parameter is the minimum value, in units of 0.01 dB. - The third parameter is the step size, in units of 0.01 dB. - Set the fourth parameter to 1 if the minimum value actually mutes - the control. - </para> - - <para> - The <function>DECLARE_TLV_DB_LINEAR</function> macro defines - information about a mixer control where the control's value affects - the output linearly. - The first parameter is the name of the variable to be defined. - The second parameter is the minimum value, in units of 0.01 dB. - The third parameter is the maximum value, in units of 0.01 dB. - If the minimum value mutes the control, set the second parameter to - <constant>TLV_DB_GAIN_MUTE</constant>. - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- API for AC97 Codec --> -<!-- ****************************************************** --> - <chapter id="api-ac97"> - <title>API for AC97 Codec</title> - - <section> - <title>General</title> - <para> - The ALSA AC97 codec layer is a well-defined one, and you don't - have to write much code to control it. Only low-level control - routines are necessary. The AC97 codec API is defined in - <filename><sound/ac97_codec.h></filename>. - </para> - </section> - - <section id="api-ac97-example"> - <title>Full Code Example</title> - <para> - <example> - <title>Example of AC97 Interface</title> - <programlisting> -<![CDATA[ - struct mychip { - .... - struct snd_ac97 *ac97; - .... - }; - - static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, - unsigned short reg) - { - struct mychip *chip = ac97->private_data; - .... - /* read a register value here from the codec */ - return the_register_value; - } - - static void snd_mychip_ac97_write(struct snd_ac97 *ac97, - unsigned short reg, unsigned short val) - { - struct mychip *chip = ac97->private_data; - .... - /* write the given register value to the codec */ - } - - static int snd_mychip_ac97(struct mychip *chip) - { - struct snd_ac97_bus *bus; - struct snd_ac97_template ac97; - int err; - static struct snd_ac97_bus_ops ops = { - .write = snd_mychip_ac97_write, - .read = snd_mychip_ac97_read, - }; - - err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus); - if (err < 0) - return err; - memset(&ac97, 0, sizeof(ac97)); - ac97.private_data = chip; - return snd_ac97_mixer(bus, &ac97, &chip->ac97); - } - -]]> - </programlisting> - </example> - </para> - </section> - - <section id="api-ac97-constructor"> - <title>Constructor</title> - <para> - To create an ac97 instance, first call <function>snd_ac97_bus</function> - with an <type>ac97_bus_ops_t</type> record with callback functions. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_ac97_bus *bus; - static struct snd_ac97_bus_ops ops = { - .write = snd_mychip_ac97_write, - .read = snd_mychip_ac97_read, - }; - - snd_ac97_bus(card, 0, &ops, NULL, &pbus); -]]> - </programlisting> - </informalexample> - - The bus record is shared among all belonging ac97 instances. - </para> - - <para> - And then call <function>snd_ac97_mixer()</function> with an - struct <structname>snd_ac97_template</structname> - record together with the bus pointer created above. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_ac97_template ac97; - int err; - - memset(&ac97, 0, sizeof(ac97)); - ac97.private_data = chip; - snd_ac97_mixer(bus, &ac97, &chip->ac97); -]]> - </programlisting> - </informalexample> - - where chip->ac97 is a pointer to a newly created - <type>ac97_t</type> instance. - In this case, the chip pointer is set as the private data, so that - the read/write callback functions can refer to this chip instance. - This instance is not necessarily stored in the chip - record. If you need to change the register values from the - driver, or need the suspend/resume of ac97 codecs, keep this - pointer to pass to the corresponding functions. - </para> - </section> - - <section id="api-ac97-callbacks"> - <title>Callbacks</title> - <para> - The standard callbacks are <structfield>read</structfield> and - <structfield>write</structfield>. Obviously they - correspond to the functions for read and write accesses to the - hardware low-level codes. - </para> - - <para> - The <structfield>read</structfield> callback returns the - register value specified in the argument. - - <informalexample> - <programlisting> -<![CDATA[ - static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, - unsigned short reg) - { - struct mychip *chip = ac97->private_data; - .... - return the_register_value; - } -]]> - </programlisting> - </informalexample> - - Here, the chip can be cast from ac97->private_data. - </para> - - <para> - Meanwhile, the <structfield>write</structfield> callback is - used to set the register value. - - <informalexample> - <programlisting> -<![CDATA[ - static void snd_mychip_ac97_write(struct snd_ac97 *ac97, - unsigned short reg, unsigned short val) -]]> - </programlisting> - </informalexample> - </para> - - <para> - These callbacks are non-atomic like the control API callbacks. - </para> - - <para> - There are also other callbacks: - <structfield>reset</structfield>, - <structfield>wait</structfield> and - <structfield>init</structfield>. - </para> - - <para> - The <structfield>reset</structfield> callback is used to reset - the codec. If the chip requires a special kind of reset, you can - define this callback. - </para> - - <para> - The <structfield>wait</structfield> callback is used to - add some waiting time in the standard initialization of the codec. If the - chip requires the extra waiting time, define this callback. - </para> - - <para> - The <structfield>init</structfield> callback is used for - additional initialization of the codec. - </para> - </section> - - <section id="api-ac97-updating-registers"> - <title>Updating Registers in The Driver</title> - <para> - If you need to access to the codec from the driver, you can - call the following functions: - <function>snd_ac97_write()</function>, - <function>snd_ac97_read()</function>, - <function>snd_ac97_update()</function> and - <function>snd_ac97_update_bits()</function>. - </para> - - <para> - Both <function>snd_ac97_write()</function> and - <function>snd_ac97_update()</function> functions are used to - set a value to the given register - (<constant>AC97_XXX</constant>). The difference between them is - that <function>snd_ac97_update()</function> doesn't write a - value if the given value has been already set, while - <function>snd_ac97_write()</function> always rewrites the - value. - - <informalexample> - <programlisting> -<![CDATA[ - snd_ac97_write(ac97, AC97_MASTER, 0x8080); - snd_ac97_update(ac97, AC97_MASTER, 0x8080); -]]> - </programlisting> - </informalexample> - </para> - - <para> - <function>snd_ac97_read()</function> is used to read the value - of the given register. For example, - - <informalexample> - <programlisting> -<![CDATA[ - value = snd_ac97_read(ac97, AC97_MASTER); -]]> - </programlisting> - </informalexample> - </para> - - <para> - <function>snd_ac97_update_bits()</function> is used to update - some bits in the given register. - - <informalexample> - <programlisting> -<![CDATA[ - snd_ac97_update_bits(ac97, reg, mask, value); -]]> - </programlisting> - </informalexample> - </para> - - <para> - Also, there is a function to change the sample rate (of a - given register such as - <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or - DRA is supported by the codec: - <function>snd_ac97_set_rate()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The following registers are available to set the rate: - <constant>AC97_PCM_MIC_ADC_RATE</constant>, - <constant>AC97_PCM_FRONT_DAC_RATE</constant>, - <constant>AC97_PCM_LR_ADC_RATE</constant>, - <constant>AC97_SPDIF</constant>. When - <constant>AC97_SPDIF</constant> is specified, the register is - not really changed but the corresponding IEC958 status bits will - be updated. - </para> - </section> - - <section id="api-ac97-clock-adjustment"> - <title>Clock Adjustment</title> - <para> - In some chips, the clock of the codec isn't 48000 but using a - PCI clock (to save a quartz!). In this case, change the field - bus->clock to the corresponding - value. For example, intel8x0 - and es1968 drivers have their own function to read from the clock. - </para> - </section> - - <section id="api-ac97-proc-files"> - <title>Proc Files</title> - <para> - The ALSA AC97 interface will create a proc file such as - <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and - <filename>ac97#0-0+regs</filename>. You can refer to these files to - see the current status and registers of the codec. - </para> - </section> - - <section id="api-ac97-multiple-codecs"> - <title>Multiple Codecs</title> - <para> - When there are several codecs on the same card, you need to - call <function>snd_ac97_mixer()</function> multiple times with - ac97.num=1 or greater. The <structfield>num</structfield> field - specifies the codec number. - </para> - - <para> - If you set up multiple codecs, you either need to write - different callbacks for each codec or check - ac97->num in the callback routines. - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- MIDI (MPU401-UART) Interface --> -<!-- ****************************************************** --> - <chapter id="midi-interface"> - <title>MIDI (MPU401-UART) Interface</title> - - <section id="midi-interface-general"> - <title>General</title> - <para> - Many soundcards have built-in MIDI (MPU401-UART) - interfaces. When the soundcard supports the standard MPU401-UART - interface, most likely you can use the ALSA MPU401-UART API. The - MPU401-UART API is defined in - <filename><sound/mpu401.h></filename>. - </para> - - <para> - Some soundchips have a similar but slightly different - implementation of mpu401 stuff. For example, emu10k1 has its own - mpu401 routines. - </para> - </section> - - <section id="midi-interface-constructor"> - <title>Constructor</title> - <para> - To create a rawmidi object, call - <function>snd_mpu401_uart_new()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_rawmidi *rmidi; - snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags, - irq, &rmidi); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The first argument is the card pointer, and the second is the - index of this component. You can create up to 8 rawmidi - devices. - </para> - - <para> - The third argument is the type of the hardware, - <constant>MPU401_HW_XXX</constant>. If it's not a special one, - you can use <constant>MPU401_HW_MPU401</constant>. - </para> - - <para> - The 4th argument is the I/O port address. Many - backward-compatible MPU401 have an I/O port such as 0x330. Or, it - might be a part of its own PCI I/O region. It depends on the - chip design. - </para> - - <para> - The 5th argument is a bitflag for additional information. - When the I/O port address above is part of the PCI I/O - region, the MPU401 I/O port might have been already allocated - (reserved) by the driver itself. In such a case, pass a bit flag - <constant>MPU401_INFO_INTEGRATED</constant>, - and the mpu401-uart layer will allocate the I/O ports by itself. - </para> - - <para> - When the controller supports only the input or output MIDI stream, - pass the <constant>MPU401_INFO_INPUT</constant> or - <constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively. - Then the rawmidi instance is created as a single stream. - </para> - - <para> - <constant>MPU401_INFO_MMIO</constant> bitflag is used to change - the access method to MMIO (via readb and writeb) instead of - iob and outb. In this case, you have to pass the iomapped address - to <function>snd_mpu401_uart_new()</function>. - </para> - - <para> - When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output - stream isn't checked in the default interrupt handler. The driver - needs to call <function>snd_mpu401_uart_interrupt_tx()</function> - by itself to start processing the output stream in the irq handler. - </para> - - <para> - If the MPU-401 interface shares its interrupt with the other logical - devices on the card, set <constant>MPU401_INFO_IRQ_HOOK</constant> - (see <link linkend="midi-interface-interrupt-handler"><citetitle> - below</citetitle></link>). - </para> - - <para> - Usually, the port address corresponds to the command port and - port + 1 corresponds to the data port. If not, you may change - the <structfield>cport</structfield> field of - struct <structname>snd_mpu401</structname> manually - afterward. However, <structname>snd_mpu401</structname> pointer is not - returned explicitly by - <function>snd_mpu401_uart_new()</function>. You need to cast - rmidi->private_data to - <structname>snd_mpu401</structname> explicitly, - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_mpu401 *mpu; - mpu = rmidi->private_data; -]]> - </programlisting> - </informalexample> - - and reset the cport as you like: - - <informalexample> - <programlisting> -<![CDATA[ - mpu->cport = my_own_control_port; -]]> - </programlisting> - </informalexample> - </para> - - <para> - The 6th argument specifies the ISA irq number that will be - allocated. If no interrupt is to be allocated (because your - code is already allocating a shared interrupt, or because the - device does not use interrupts), pass -1 instead. - For a MPU-401 device without an interrupt, a polling timer - will be used instead. - </para> - </section> - - <section id="midi-interface-interrupt-handler"> - <title>Interrupt Handler</title> - <para> - When the interrupt is allocated in - <function>snd_mpu401_uart_new()</function>, an exclusive ISA - interrupt handler is automatically used, hence you don't have - anything else to do than creating the mpu401 stuff. Otherwise, you - have to set <constant>MPU401_INFO_IRQ_HOOK</constant>, and call - <function>snd_mpu401_uart_interrupt()</function> explicitly from your - own interrupt handler when it has determined that a UART interrupt - has occurred. - </para> - - <para> - In this case, you need to pass the private_data of the - returned rawmidi object from - <function>snd_mpu401_uart_new()</function> as the second - argument of <function>snd_mpu401_uart_interrupt()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs); -]]> - </programlisting> - </informalexample> - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- RawMIDI Interface --> -<!-- ****************************************************** --> - <chapter id="rawmidi-interface"> - <title>RawMIDI Interface</title> - - <section id="rawmidi-interface-overview"> - <title>Overview</title> - - <para> - The raw MIDI interface is used for hardware MIDI ports that can - be accessed as a byte stream. It is not used for synthesizer - chips that do not directly understand MIDI. - </para> - - <para> - ALSA handles file and buffer management. All you have to do is - to write some code to move data between the buffer and the - hardware. - </para> - - <para> - The rawmidi API is defined in - <filename><sound/rawmidi.h></filename>. - </para> - </section> - - <section id="rawmidi-interface-constructor"> - <title>Constructor</title> - - <para> - To create a rawmidi device, call the - <function>snd_rawmidi_new</function> function: - <informalexample> - <programlisting> -<![CDATA[ - struct snd_rawmidi *rmidi; - err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi); - if (err < 0) - return err; - rmidi->private_data = chip; - strcpy(rmidi->name, "My MIDI"); - rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT | - SNDRV_RAWMIDI_INFO_INPUT | - SNDRV_RAWMIDI_INFO_DUPLEX; -]]> - </programlisting> - </informalexample> - </para> - - <para> - The first argument is the card pointer, the second argument is - the ID string. - </para> - - <para> - The third argument is the index of this component. You can - create up to 8 rawmidi devices. - </para> - - <para> - The fourth and fifth arguments are the number of output and - input substreams, respectively, of this device (a substream is - the equivalent of a MIDI port). - </para> - - <para> - Set the <structfield>info_flags</structfield> field to specify - the capabilities of the device. - Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is - at least one output port, - <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at - least one input port, - and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device - can handle output and input at the same time. - </para> - - <para> - After the rawmidi device is created, you need to set the - operators (callbacks) for each substream. There are helper - functions to set the operators for all the substreams of a device: - <informalexample> - <programlisting> -<![CDATA[ - snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops); - snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The operators are usually defined like this: - <informalexample> - <programlisting> -<![CDATA[ - static struct snd_rawmidi_ops snd_mymidi_output_ops = { - .open = snd_mymidi_output_open, - .close = snd_mymidi_output_close, - .trigger = snd_mymidi_output_trigger, - }; -]]> - </programlisting> - </informalexample> - These callbacks are explained in the <link - linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link> - section. - </para> - - <para> - If there are more than one substream, you should give a - unique name to each of them: - <informalexample> - <programlisting> -<![CDATA[ - struct snd_rawmidi_substream *substream; - list_for_each_entry(substream, - &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams, - list { - sprintf(substream->name, "My MIDI Port %d", substream->number + 1); - } - /* same for SNDRV_RAWMIDI_STREAM_INPUT */ -]]> - </programlisting> - </informalexample> - </para> - </section> - - <section id="rawmidi-interface-callbacks"> - <title>Callbacks</title> - - <para> - In all the callbacks, the private data that you've set for the - rawmidi device can be accessed as - substream->rmidi->private_data. - <!-- <code> isn't available before DocBook 4.3 --> - </para> - - <para> - If there is more than one port, your callbacks can determine the - port index from the struct snd_rawmidi_substream data passed to each - callback: - <informalexample> - <programlisting> -<![CDATA[ - struct snd_rawmidi_substream *substream; - int index = substream->number; -]]> - </programlisting> - </informalexample> - </para> - - <section id="rawmidi-interface-op-open"> - <title><function>open</function> callback</title> - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_open(struct snd_rawmidi_substream *substream); -]]> - </programlisting> - </informalexample> - - <para> - This is called when a substream is opened. - You can initialize the hardware here, but you shouldn't - start transmitting/receiving data yet. - </para> - </section> - - <section id="rawmidi-interface-op-close"> - <title><function>close</function> callback</title> - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_xxx_close(struct snd_rawmidi_substream *substream); -]]> - </programlisting> - </informalexample> - - <para> - Guess what. - </para> - - <para> - The <function>open</function> and <function>close</function> - callbacks of a rawmidi device are serialized with a mutex, - and can sleep. - </para> - </section> - - <section id="rawmidi-interface-op-trigger-out"> - <title><function>trigger</function> callback for output - substreams</title> - - <informalexample> - <programlisting> -<![CDATA[ - static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up); -]]> - </programlisting> - </informalexample> - - <para> - This is called with a nonzero <parameter>up</parameter> - parameter when there is some data in the substream buffer that - must be transmitted. - </para> - - <para> - To read data from the buffer, call - <function>snd_rawmidi_transmit_peek</function>. It will - return the number of bytes that have been read; this will be - less than the number of bytes requested when there are no more - data in the buffer. - After the data have been transmitted successfully, call - <function>snd_rawmidi_transmit_ack</function> to remove the - data from the substream buffer: - <informalexample> - <programlisting> -<![CDATA[ - unsigned char data; - while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) { - if (snd_mychip_try_to_transmit(data)) - snd_rawmidi_transmit_ack(substream, 1); - else - break; /* hardware FIFO full */ - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - If you know beforehand that the hardware will accept data, you - can use the <function>snd_rawmidi_transmit</function> function - which reads some data and removes them from the buffer at once: - <informalexample> - <programlisting> -<![CDATA[ - while (snd_mychip_transmit_possible()) { - unsigned char data; - if (snd_rawmidi_transmit(substream, &data, 1) != 1) - break; /* no more data */ - snd_mychip_transmit(data); - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - If you know beforehand how many bytes you can accept, you can - use a buffer size greater than one with the - <function>snd_rawmidi_transmit*</function> functions. - </para> - - <para> - The <function>trigger</function> callback must not sleep. If - the hardware FIFO is full before the substream buffer has been - emptied, you have to continue transmitting data later, either - in an interrupt handler, or with a timer if the hardware - doesn't have a MIDI transmit interrupt. - </para> - - <para> - The <function>trigger</function> callback is called with a - zero <parameter>up</parameter> parameter when the transmission - of data should be aborted. - </para> - </section> - - <section id="rawmidi-interface-op-trigger-in"> - <title><function>trigger</function> callback for input - substreams</title> - - <informalexample> - <programlisting> -<![CDATA[ - static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up); -]]> - </programlisting> - </informalexample> - - <para> - This is called with a nonzero <parameter>up</parameter> - parameter to enable receiving data, or with a zero - <parameter>up</parameter> parameter do disable receiving data. - </para> - - <para> - The <function>trigger</function> callback must not sleep; the - actual reading of data from the device is usually done in an - interrupt handler. - </para> - - <para> - When data reception is enabled, your interrupt handler should - call <function>snd_rawmidi_receive</function> for all received - data: - <informalexample> - <programlisting> -<![CDATA[ - void snd_mychip_midi_interrupt(...) - { - while (mychip_midi_available()) { - unsigned char data; - data = mychip_midi_read(); - snd_rawmidi_receive(substream, &data, 1); - } - } -]]> - </programlisting> - </informalexample> - </para> - </section> - - <section id="rawmidi-interface-op-drain"> - <title><function>drain</function> callback</title> - - <informalexample> - <programlisting> -<![CDATA[ - static void snd_xxx_drain(struct snd_rawmidi_substream *substream); -]]> - </programlisting> - </informalexample> - - <para> - This is only used with output substreams. This function should wait - until all data read from the substream buffer have been transmitted. - This ensures that the device can be closed and the driver unloaded - without losing data. - </para> - - <para> - This callback is optional. If you do not set - <structfield>drain</structfield> in the struct snd_rawmidi_ops - structure, ALSA will simply wait for 50 milliseconds - instead. - </para> - </section> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Miscellaneous Devices --> -<!-- ****************************************************** --> - <chapter id="misc-devices"> - <title>Miscellaneous Devices</title> - - <section id="misc-devices-opl3"> - <title>FM OPL3</title> - <para> - The FM OPL3 is still used in many chips (mainly for backward - compatibility). ALSA has a nice OPL3 FM control layer, too. The - OPL3 API is defined in - <filename><sound/opl3.h></filename>. - </para> - - <para> - FM registers can be directly accessed through the direct-FM API, - defined in <filename><sound/asound_fm.h></filename>. In - ALSA native mode, FM registers are accessed through - the Hardware-Dependent Device direct-FM extension API, whereas in - OSS compatible mode, FM registers can be accessed with the OSS - direct-FM compatible API in <filename>/dev/dmfmX</filename> device. - </para> - - <para> - To create the OPL3 component, you have two functions to - call. The first one is a constructor for the <type>opl3_t</type> - instance. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_opl3 *opl3; - snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX, - integrated, &opl3); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The first argument is the card pointer, the second one is the - left port address, and the third is the right port address. In - most cases, the right port is placed at the left port + 2. - </para> - - <para> - The fourth argument is the hardware type. - </para> - - <para> - When the left and right ports have been already allocated by - the card driver, pass non-zero to the fifth argument - (<parameter>integrated</parameter>). Otherwise, the opl3 module will - allocate the specified ports by itself. - </para> - - <para> - When the accessing the hardware requires special method - instead of the standard I/O access, you can create opl3 instance - separately with <function>snd_opl3_new()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_opl3 *opl3; - snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3); -]]> - </programlisting> - </informalexample> - </para> - - <para> - Then set <structfield>command</structfield>, - <structfield>private_data</structfield> and - <structfield>private_free</structfield> for the private - access function, the private data and the destructor. - The l_port and r_port are not necessarily set. Only the - command must be set properly. You can retrieve the data - from the opl3->private_data field. - </para> - - <para> - After creating the opl3 instance via <function>snd_opl3_new()</function>, - call <function>snd_opl3_init()</function> to initialize the chip to the - proper state. Note that <function>snd_opl3_create()</function> always - calls it internally. - </para> - - <para> - If the opl3 instance is created successfully, then create a - hwdep device for this opl3. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_hwdep *opl3hwdep; - snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The first argument is the <type>opl3_t</type> instance you - created, and the second is the index number, usually 0. - </para> - - <para> - The third argument is the index-offset for the sequencer - client assigned to the OPL3 port. When there is an MPU401-UART, - give 1 for here (UART always takes 0). - </para> - </section> - - <section id="misc-devices-hardware-dependent"> - <title>Hardware-Dependent Devices</title> - <para> - Some chips need user-space access for special - controls or for loading the micro code. In such a case, you can - create a hwdep (hardware-dependent) device. The hwdep API is - defined in <filename><sound/hwdep.h></filename>. You can - find examples in opl3 driver or - <filename>isa/sb/sb16_csp.c</filename>. - </para> - - <para> - The creation of the <type>hwdep</type> instance is done via - <function>snd_hwdep_new()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_hwdep *hw; - snd_hwdep_new(card, "My HWDEP", 0, &hw); -]]> - </programlisting> - </informalexample> - - where the third argument is the index number. - </para> - - <para> - You can then pass any pointer value to the - <parameter>private_data</parameter>. - If you assign a private data, you should define the - destructor, too. The destructor function is set in - the <structfield>private_free</structfield> field. - - <informalexample> - <programlisting> -<![CDATA[ - struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL); - hw->private_data = p; - hw->private_free = mydata_free; -]]> - </programlisting> - </informalexample> - - and the implementation of the destructor would be: - - <informalexample> - <programlisting> -<![CDATA[ - static void mydata_free(struct snd_hwdep *hw) - { - struct mydata *p = hw->private_data; - kfree(p); - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The arbitrary file operations can be defined for this - instance. The file operators are defined in - the <parameter>ops</parameter> table. For example, assume that - this chip needs an ioctl. - - <informalexample> - <programlisting> -<![CDATA[ - hw->ops.open = mydata_open; - hw->ops.ioctl = mydata_ioctl; - hw->ops.release = mydata_release; -]]> - </programlisting> - </informalexample> - - And implement the callback functions as you like. - </para> - </section> - - <section id="misc-devices-IEC958"> - <title>IEC958 (S/PDIF)</title> - <para> - Usually the controls for IEC958 devices are implemented via - the control interface. There is a macro to compose a name string for - IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function> - defined in <filename><include/asound.h></filename>. - </para> - - <para> - There are some standard controls for IEC958 status bits. These - controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>, - and the size of element is fixed as 4 bytes array - (value.iec958.status[x]). For the <structfield>info</structfield> - callback, you don't specify - the value field for this type (the count field must be set, - though). - </para> - - <para> - <quote>IEC958 Playback Con Mask</quote> is used to return the - bit-mask for the IEC958 status bits of consumer mode. Similarly, - <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for - professional mode. They are read-only controls, and are defined - as MIXER controls (iface = - <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>). - </para> - - <para> - Meanwhile, <quote>IEC958 Playback Default</quote> control is - defined for getting and setting the current default IEC958 - bits. Note that this one is usually defined as a PCM control - (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>), - although in some places it's defined as a MIXER control. - </para> - - <para> - In addition, you can define the control switches to - enable/disable or to set the raw bit mode. The implementation - will depend on the chip, but the control should be named as - <quote>IEC958 xxx</quote>, preferably using - the <function>SNDRV_CTL_NAME_IEC958()</function> macro. - </para> - - <para> - You can find several cases, for example, - <filename>pci/emu10k1</filename>, - <filename>pci/ice1712</filename>, or - <filename>pci/cmipci.c</filename>. - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Buffer and Memory Management --> -<!-- ****************************************************** --> - <chapter id="buffer-and-memory"> - <title>Buffer and Memory Management</title> - - <section id="buffer-and-memory-buffer-types"> - <title>Buffer Types</title> - <para> - ALSA provides several different buffer allocation functions - depending on the bus and the architecture. All these have a - consistent API. The allocation of physically-contiguous pages is - done via - <function>snd_malloc_xxx_pages()</function> function, where xxx - is the bus type. - </para> - - <para> - The allocation of pages with fallback is - <function>snd_malloc_xxx_pages_fallback()</function>. This - function tries to allocate the specified pages but if the pages - are not available, it tries to reduce the page sizes until - enough space is found. - </para> - - <para> - The release the pages, call - <function>snd_free_xxx_pages()</function> function. - </para> - - <para> - Usually, ALSA drivers try to allocate and reserve - a large contiguous physical space - at the time the module is loaded for the later use. - This is called <quote>pre-allocation</quote>. - As already written, you can call the following function at - pcm instance construction time (in the case of PCI bus). - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, - snd_dma_pci_data(pci), size, max); -]]> - </programlisting> - </informalexample> - - where <parameter>size</parameter> is the byte size to be - pre-allocated and the <parameter>max</parameter> is the maximum - size to be changed via the <filename>prealloc</filename> proc file. - The allocator will try to get an area as large as possible - within the given size. - </para> - - <para> - The second argument (type) and the third argument (device pointer) - are dependent on the bus. - In the case of the ISA bus, pass <function>snd_dma_isa_data()</function> - as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type. - For the continuous buffer unrelated to the bus can be pre-allocated - with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the - <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer, - where <constant>GFP_KERNEL</constant> is the kernel allocation flag to - use. - For the PCI scatter-gather buffers, use - <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with - <function>snd_dma_pci_data(pci)</function> - (see the - <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers - </citetitle></link> section). - </para> - - <para> - Once the buffer is pre-allocated, you can use the - allocator in the <structfield>hw_params</structfield> callback: - - <informalexample> - <programlisting> -<![CDATA[ - snd_pcm_lib_malloc_pages(substream, size); -]]> - </programlisting> - </informalexample> - - Note that you have to pre-allocate to use this function. - </para> - </section> - - <section id="buffer-and-memory-external-hardware"> - <title>External Hardware Buffers</title> - <para> - Some chips have their own hardware buffers and the DMA - transfer from the host memory is not available. In such a case, - you need to either 1) copy/set the audio data directly to the - external hardware buffer, or 2) make an intermediate buffer and - copy/set the data from it to the external hardware buffer in - interrupts (or in tasklets, preferably). - </para> - - <para> - The first case works fine if the external hardware buffer is large - enough. This method doesn't need any extra buffers and thus is - more effective. You need to define the - <structfield>copy</structfield> and - <structfield>silence</structfield> callbacks for - the data transfer. However, there is a drawback: it cannot - be mmapped. The examples are GUS's GF1 PCM or emu8000's - wavetable PCM. - </para> - - <para> - The second case allows for mmap on the buffer, although you have - to handle an interrupt or a tasklet to transfer the data - from the intermediate buffer to the hardware buffer. You can find an - example in the vxpocket driver. - </para> - - <para> - Another case is when the chip uses a PCI memory-map - region for the buffer instead of the host memory. In this case, - mmap is available only on certain architectures like the Intel one. - In non-mmap mode, the data cannot be transferred as in the normal - way. Thus you need to define the <structfield>copy</structfield> and - <structfield>silence</structfield> callbacks as well, - as in the cases above. The examples are found in - <filename>rme32.c</filename> and <filename>rme96.c</filename>. - </para> - - <para> - The implementation of the <structfield>copy</structfield> and - <structfield>silence</structfield> callbacks depends upon - whether the hardware supports interleaved or non-interleaved - samples. The <structfield>copy</structfield> callback is - defined like below, a bit - differently depending whether the direction is playback or - capture: - - <informalexample> - <programlisting> -<![CDATA[ - static int playback_copy(struct snd_pcm_substream *substream, int channel, - snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count); - static int capture_copy(struct snd_pcm_substream *substream, int channel, - snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count); -]]> - </programlisting> - </informalexample> - </para> - - <para> - In the case of interleaved samples, the second argument - (<parameter>channel</parameter>) is not used. The third argument - (<parameter>pos</parameter>) points the - current position offset in frames. - </para> - - <para> - The meaning of the fourth argument is different between - playback and capture. For playback, it holds the source data - pointer, and for capture, it's the destination data pointer. - </para> - - <para> - The last argument is the number of frames to be copied. - </para> - - <para> - What you have to do in this callback is again different - between playback and capture directions. In the - playback case, you copy the given amount of data - (<parameter>count</parameter>) at the specified pointer - (<parameter>src</parameter>) to the specified offset - (<parameter>pos</parameter>) on the hardware buffer. When - coded like memcpy-like way, the copy would be like: - - <informalexample> - <programlisting> -<![CDATA[ - my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src, - frames_to_bytes(runtime, count)); -]]> - </programlisting> - </informalexample> - </para> - - <para> - For the capture direction, you copy the given amount of - data (<parameter>count</parameter>) at the specified offset - (<parameter>pos</parameter>) on the hardware buffer to the - specified pointer (<parameter>dst</parameter>). - - <informalexample> - <programlisting> -<![CDATA[ - my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos), - frames_to_bytes(runtime, count)); -]]> - </programlisting> - </informalexample> - - Note that both the position and the amount of data are given - in frames. - </para> - - <para> - In the case of non-interleaved samples, the implementation - will be a bit more complicated. - </para> - - <para> - You need to check the channel argument, and if it's -1, copy - the whole channels. Otherwise, you have to copy only the - specified channel. Please check - <filename>isa/gus/gus_pcm.c</filename> as an example. - </para> - - <para> - The <structfield>silence</structfield> callback is also - implemented in a similar way. - - <informalexample> - <programlisting> -<![CDATA[ - static int silence(struct snd_pcm_substream *substream, int channel, - snd_pcm_uframes_t pos, snd_pcm_uframes_t count); -]]> - </programlisting> - </informalexample> - </para> - - <para> - The meanings of arguments are the same as in the - <structfield>copy</structfield> - callback, although there is no <parameter>src/dst</parameter> - argument. In the case of interleaved samples, the channel - argument has no meaning, as well as on - <structfield>copy</structfield> callback. - </para> - - <para> - The role of <structfield>silence</structfield> callback is to - set the given amount - (<parameter>count</parameter>) of silence data at the - specified offset (<parameter>pos</parameter>) on the hardware - buffer. Suppose that the data format is signed (that is, the - silent-data is 0), and the implementation using a memset-like - function would be like: - - <informalexample> - <programlisting> -<![CDATA[ - my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0, - frames_to_bytes(runtime, count)); -]]> - </programlisting> - </informalexample> - </para> - - <para> - In the case of non-interleaved samples, again, the - implementation becomes a bit more complicated. See, for example, - <filename>isa/gus/gus_pcm.c</filename>. - </para> - </section> - - <section id="buffer-and-memory-non-contiguous"> - <title>Non-Contiguous Buffers</title> - <para> - If your hardware supports the page table as in emu10k1 or the - buffer descriptors as in via82xx, you can use the scatter-gather - (SG) DMA. ALSA provides an interface for handling SG-buffers. - The API is provided in <filename><sound/pcm.h></filename>. - </para> - - <para> - For creating the SG-buffer handler, call - <function>snd_pcm_lib_preallocate_pages()</function> or - <function>snd_pcm_lib_preallocate_pages_for_all()</function> - with <constant>SNDRV_DMA_TYPE_DEV_SG</constant> - in the PCM constructor like other PCI pre-allocator. - You need to pass <function>snd_dma_pci_data(pci)</function>, - where pci is the struct <structname>pci_dev</structname> pointer - of the chip as well. - The <type>struct snd_sg_buf</type> instance is created as - substream->dma_private. You can cast - the pointer like: - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private; -]]> - </programlisting> - </informalexample> - </para> - - <para> - Then call <function>snd_pcm_lib_malloc_pages()</function> - in the <structfield>hw_params</structfield> callback - as well as in the case of normal PCI buffer. - The SG-buffer handler will allocate the non-contiguous kernel - pages of the given size and map them onto the virtually contiguous - memory. The virtual pointer is addressed in runtime->dma_area. - The physical address (runtime->dma_addr) is set to zero, - because the buffer is physically non-contiguous. - The physical address table is set up in sgbuf->table. - You can get the physical address at a certain offset via - <function>snd_pcm_sgbuf_get_addr()</function>. - </para> - - <para> - When a SG-handler is used, you need to set - <function>snd_pcm_sgbuf_ops_page</function> as - the <structfield>page</structfield> callback. - (See <link linkend="pcm-interface-operators-page-callback"> - <citetitle>page callback section</citetitle></link>.) - </para> - - <para> - To release the data, call - <function>snd_pcm_lib_free_pages()</function> in the - <structfield>hw_free</structfield> callback as usual. - </para> - </section> - - <section id="buffer-and-memory-vmalloced"> - <title>Vmalloc'ed Buffers</title> - <para> - It's possible to use a buffer allocated via - <function>vmalloc</function>, for example, for an intermediate - buffer. Since the allocated pages are not contiguous, you need - to set the <structfield>page</structfield> callback to obtain - the physical address at every offset. - </para> - - <para> - The implementation of <structfield>page</structfield> callback - would be like this: - - <informalexample> - <programlisting> -<![CDATA[ - #include <linux/vmalloc.h> - - /* get the physical page pointer on the given offset */ - static struct page *mychip_page(struct snd_pcm_substream *substream, - unsigned long offset) - { - void *pageptr = substream->runtime->dma_area + offset; - return vmalloc_to_page(pageptr); - } -]]> - </programlisting> - </informalexample> - </para> - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Proc Interface --> -<!-- ****************************************************** --> - <chapter id="proc-interface"> - <title>Proc Interface</title> - <para> - ALSA provides an easy interface for procfs. The proc files are - very useful for debugging. I recommend you set up proc files if - you write a driver and want to get a running status or register - dumps. The API is found in - <filename><sound/info.h></filename>. - </para> - - <para> - To create a proc file, call - <function>snd_card_proc_new()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - struct snd_info_entry *entry; - int err = snd_card_proc_new(card, "my-file", &entry); -]]> - </programlisting> - </informalexample> - - where the second argument specifies the name of the proc file to be - created. The above example will create a file - <filename>my-file</filename> under the card directory, - e.g. <filename>/proc/asound/card0/my-file</filename>. - </para> - - <para> - Like other components, the proc entry created via - <function>snd_card_proc_new()</function> will be registered and - released automatically in the card registration and release - functions. - </para> - - <para> - When the creation is successful, the function stores a new - instance in the pointer given in the third argument. - It is initialized as a text proc file for read only. To use - this proc file as a read-only text file as it is, set the read - callback with a private data via - <function>snd_info_set_text_ops()</function>. - - <informalexample> - <programlisting> -<![CDATA[ - snd_info_set_text_ops(entry, chip, my_proc_read); -]]> - </programlisting> - </informalexample> - - where the second argument (<parameter>chip</parameter>) is the - private data to be used in the callbacks. The third parameter - specifies the read buffer size and the fourth - (<parameter>my_proc_read</parameter>) is the callback function, which - is defined like - - <informalexample> - <programlisting> -<![CDATA[ - static void my_proc_read(struct snd_info_entry *entry, - struct snd_info_buffer *buffer); -]]> - </programlisting> - </informalexample> - - </para> - - <para> - In the read callback, use <function>snd_iprintf()</function> for - output strings, which works just like normal - <function>printf()</function>. For example, - - <informalexample> - <programlisting> -<![CDATA[ - static void my_proc_read(struct snd_info_entry *entry, - struct snd_info_buffer *buffer) - { - struct my_chip *chip = entry->private_data; - - snd_iprintf(buffer, "This is my chip!\n"); - snd_iprintf(buffer, "Port = %ld\n", chip->port); - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The file permissions can be changed afterwards. As default, it's - set as read only for all users. If you want to add write - permission for the user (root as default), do as follows: - - <informalexample> - <programlisting> -<![CDATA[ - entry->mode = S_IFREG | S_IRUGO | S_IWUSR; -]]> - </programlisting> - </informalexample> - - and set the write buffer size and the callback - - <informalexample> - <programlisting> -<![CDATA[ - entry->c.text.write = my_proc_write; -]]> - </programlisting> - </informalexample> - </para> - - <para> - For the write callback, you can use - <function>snd_info_get_line()</function> to get a text line, and - <function>snd_info_get_str()</function> to retrieve a string from - the line. Some examples are found in - <filename>core/oss/mixer_oss.c</filename>, core/oss/and - <filename>pcm_oss.c</filename>. - </para> - - <para> - For a raw-data proc-file, set the attributes as follows: - - <informalexample> - <programlisting> -<![CDATA[ - static struct snd_info_entry_ops my_file_io_ops = { - .read = my_file_io_read, - }; - - entry->content = SNDRV_INFO_CONTENT_DATA; - entry->private_data = chip; - entry->c.ops = &my_file_io_ops; - entry->size = 4096; - entry->mode = S_IFREG | S_IRUGO; -]]> - </programlisting> - </informalexample> - - For the raw data, <structfield>size</structfield> field must be - set properly. This specifies the maximum size of the proc file access. - </para> - - <para> - The read/write callbacks of raw mode are more direct than the text mode. - You need to use a low-level I/O functions such as - <function>copy_from/to_user()</function> to transfer the - data. - - <informalexample> - <programlisting> -<![CDATA[ - static ssize_t my_file_io_read(struct snd_info_entry *entry, - void *file_private_data, - struct file *file, - char *buf, - size_t count, - loff_t pos) - { - if (copy_to_user(buf, local_data + pos, count)) - return -EFAULT; - return count; - } -]]> - </programlisting> - </informalexample> - - If the size of the info entry has been set up properly, - <structfield>count</structfield> and <structfield>pos</structfield> are - guaranteed to fit within 0 and the given size. - You don't have to check the range in the callbacks unless any - other condition is required. - - </para> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Power Management --> -<!-- ****************************************************** --> - <chapter id="power-management"> - <title>Power Management</title> - <para> - If the chip is supposed to work with suspend/resume - functions, you need to add power-management code to the - driver. The additional code for power-management should be - <function>ifdef</function>'ed with - <constant>CONFIG_PM</constant>. - </para> - - <para> - If the driver <emphasis>fully</emphasis> supports suspend/resume - that is, the device can be - properly resumed to its state when suspend was called, - you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag - in the pcm info field. Usually, this is possible when the - registers of the chip can be safely saved and restored to - RAM. If this is set, the trigger callback is called with - <constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume - callback completes. - </para> - - <para> - Even if the driver doesn't support PM fully but - partial suspend/resume is still possible, it's still worthy to - implement suspend/resume callbacks. In such a case, applications - would reset the status by calling - <function>snd_pcm_prepare()</function> and restart the stream - appropriately. Hence, you can define suspend/resume callbacks - below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant> - info flag to the PCM. - </para> - - <para> - Note that the trigger with SUSPEND can always be called when - <function>snd_pcm_suspend_all</function> is called, - regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag. - The <constant>RESUME</constant> flag affects only the behavior - of <function>snd_pcm_resume()</function>. - (Thus, in theory, - <constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed - to be handled in the trigger callback when no - <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But, - it's better to keep it for compatibility reasons.) - </para> - <para> - In the earlier version of ALSA drivers, a common - power-management layer was provided, but it has been removed. - The driver needs to define the suspend/resume hooks according to - the bus the device is connected to. In the case of PCI drivers, the - callbacks look like below: - - <informalexample> - <programlisting> -<![CDATA[ - #ifdef CONFIG_PM - static int snd_my_suspend(struct pci_dev *pci, pm_message_t state) - { - .... /* do things for suspend */ - return 0; - } - static int snd_my_resume(struct pci_dev *pci) - { - .... /* do things for suspend */ - return 0; - } - #endif -]]> - </programlisting> - </informalexample> - </para> - - <para> - The scheme of the real suspend job is as follows. - - <orderedlist> - <listitem><para>Retrieve the card and the chip data.</para></listitem> - <listitem><para>Call <function>snd_power_change_state()</function> with - <constant>SNDRV_CTL_POWER_D3hot</constant> to change the - power status.</para></listitem> - <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem> - <listitem><para>If AC97 codecs are used, call - <function>snd_ac97_suspend()</function> for each codec.</para></listitem> - <listitem><para>Save the register values if necessary.</para></listitem> - <listitem><para>Stop the hardware if necessary.</para></listitem> - <listitem><para>Disable the PCI device by calling - <function>pci_disable_device()</function>. Then, call - <function>pci_save_state()</function> at last.</para></listitem> - </orderedlist> - </para> - - <para> - A typical code would be like: - - <informalexample> - <programlisting> -<![CDATA[ - static int mychip_suspend(struct pci_dev *pci, pm_message_t state) - { - /* (1) */ - struct snd_card *card = pci_get_drvdata(pci); - struct mychip *chip = card->private_data; - /* (2) */ - snd_power_change_state(card, SNDRV_CTL_POWER_D3hot); - /* (3) */ - snd_pcm_suspend_all(chip->pcm); - /* (4) */ - snd_ac97_suspend(chip->ac97); - /* (5) */ - snd_mychip_save_registers(chip); - /* (6) */ - snd_mychip_stop_hardware(chip); - /* (7) */ - pci_disable_device(pci); - pci_save_state(pci); - return 0; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - The scheme of the real resume job is as follows. - - <orderedlist> - <listitem><para>Retrieve the card and the chip data.</para></listitem> - <listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>. - Then enable the pci device again by calling <function>pci_enable_device()</function>. - Call <function>pci_set_master()</function> if necessary, too.</para></listitem> - <listitem><para>Re-initialize the chip.</para></listitem> - <listitem><para>Restore the saved registers if necessary.</para></listitem> - <listitem><para>Resume the mixer, e.g. calling - <function>snd_ac97_resume()</function>.</para></listitem> - <listitem><para>Restart the hardware (if any).</para></listitem> - <listitem><para>Call <function>snd_power_change_state()</function> with - <constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem> - </orderedlist> - </para> - - <para> - A typical code would be like: - - <informalexample> - <programlisting> -<![CDATA[ - static int mychip_resume(struct pci_dev *pci) - { - /* (1) */ - struct snd_card *card = pci_get_drvdata(pci); - struct mychip *chip = card->private_data; - /* (2) */ - pci_restore_state(pci); - pci_enable_device(pci); - pci_set_master(pci); - /* (3) */ - snd_mychip_reinit_chip(chip); - /* (4) */ - snd_mychip_restore_registers(chip); - /* (5) */ - snd_ac97_resume(chip->ac97); - /* (6) */ - snd_mychip_restart_chip(chip); - /* (7) */ - snd_power_change_state(card, SNDRV_CTL_POWER_D0); - return 0; - } -]]> - </programlisting> - </informalexample> - </para> - - <para> - As shown in the above, it's better to save registers after - suspending the PCM operations via - <function>snd_pcm_suspend_all()</function> or - <function>snd_pcm_suspend()</function>. It means that the PCM - streams are already stopped when the register snapshot is - taken. But, remember that you don't have to restart the PCM - stream in the resume callback. It'll be restarted via - trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant> - when necessary. - </para> - - <para> - OK, we have all callbacks now. Let's set them up. In the - initialization of the card, make sure that you can get the chip - data from the card instance, typically via - <structfield>private_data</structfield> field, in case you - created the chip data individually. - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_mychip_probe(struct pci_dev *pci, - const struct pci_device_id *pci_id) - { - .... - struct snd_card *card; - struct mychip *chip; - int err; - .... - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - 0, &card); - .... - chip = kzalloc(sizeof(*chip), GFP_KERNEL); - .... - card->private_data = chip; - .... - } -]]> - </programlisting> - </informalexample> - - When you created the chip data with - <function>snd_card_new()</function>, it's anyway accessible - via <structfield>private_data</structfield> field. - - <informalexample> - <programlisting> -<![CDATA[ - static int snd_mychip_probe(struct pci_dev *pci, - const struct pci_device_id *pci_id) - { - .... - struct snd_card *card; - struct mychip *chip; - int err; - .... - err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, - sizeof(struct mychip), &card); - .... - chip = card->private_data; - .... - } -]]> - </programlisting> - </informalexample> - - </para> - - <para> - If you need a space to save the registers, allocate the - buffer for it here, too, since it would be fatal - if you cannot allocate a memory in the suspend phase. - The allocated buffer should be released in the corresponding - destructor. - </para> - - <para> - And next, set suspend/resume callbacks to the pci_driver. - - <informalexample> - <programlisting> -<![CDATA[ - static struct pci_driver driver = { - .name = KBUILD_MODNAME, - .id_table = snd_my_ids, - .probe = snd_my_probe, - .remove = snd_my_remove, - #ifdef CONFIG_PM - .suspend = snd_my_suspend, - .resume = snd_my_resume, - #endif - }; -]]> - </programlisting> - </informalexample> - </para> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Module Parameters --> -<!-- ****************************************************** --> - <chapter id="module-parameters"> - <title>Module Parameters</title> - <para> - There are standard module options for ALSA. At least, each - module should have the <parameter>index</parameter>, - <parameter>id</parameter> and <parameter>enable</parameter> - options. - </para> - - <para> - If the module supports multiple cards (usually up to - 8 = <constant>SNDRV_CARDS</constant> cards), they should be - arrays. The default initial values are defined already as - constants for easier programming: - - <informalexample> - <programlisting> -<![CDATA[ - static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; - static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; - static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; -]]> - </programlisting> - </informalexample> - </para> - - <para> - If the module supports only a single card, they could be single - variables, instead. <parameter>enable</parameter> option is not - always necessary in this case, but it would be better to have a - dummy option for compatibility. - </para> - - <para> - The module parameters must be declared with the standard - <function>module_param()()</function>, - <function>module_param_array()()</function> and - <function>MODULE_PARM_DESC()</function> macros. - </para> - - <para> - The typical coding would be like below: - - <informalexample> - <programlisting> -<![CDATA[ - #define CARD_NAME "My Chip" - - module_param_array(index, int, NULL, 0444); - MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard."); - module_param_array(id, charp, NULL, 0444); - MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard."); - module_param_array(enable, bool, NULL, 0444); - MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard."); -]]> - </programlisting> - </informalexample> - </para> - - <para> - Also, don't forget to define the module description, classes, - license and devices. Especially, the recent modprobe requires to - define the module license as GPL, etc., otherwise the system is - shown as <quote>tainted</quote>. - - <informalexample> - <programlisting> -<![CDATA[ - MODULE_DESCRIPTION("My Chip"); - MODULE_LICENSE("GPL"); - MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}"); -]]> - </programlisting> - </informalexample> - </para> - - </chapter> - - -<!-- ****************************************************** --> -<!-- How To Put Your Driver --> -<!-- ****************************************************** --> - <chapter id="how-to-put-your-driver"> - <title>How To Put Your Driver Into ALSA Tree</title> - <section> - <title>General</title> - <para> - So far, you've learned how to write the driver codes. - And you might have a question now: how to put my own - driver into the ALSA driver tree? - Here (finally :) the standard procedure is described briefly. - </para> - - <para> - Suppose that you create a new PCI driver for the card - <quote>xyz</quote>. The card module name would be - snd-xyz. The new driver is usually put into the alsa-driver - tree, <filename>alsa-driver/pci</filename> directory in - the case of PCI cards. - Then the driver is evaluated, audited and tested - by developers and users. After a certain time, the driver - will go to the alsa-kernel tree (to the corresponding directory, - such as <filename>alsa-kernel/pci</filename>) and eventually - will be integrated into the Linux 2.6 tree (the directory would be - <filename>linux/sound/pci</filename>). - </para> - - <para> - In the following sections, the driver code is supposed - to be put into alsa-driver tree. The two cases are covered: - a driver consisting of a single source file and one consisting - of several source files. - </para> - </section> - - <section> - <title>Driver with A Single Source File</title> - <para> - <orderedlist> - <listitem> - <para> - Modify alsa-driver/pci/Makefile - </para> - - <para> - Suppose you have a file xyz.c. Add the following - two lines - <informalexample> - <programlisting> -<![CDATA[ - snd-xyz-objs := xyz.o - obj-$(CONFIG_SND_XYZ) += snd-xyz.o -]]> - </programlisting> - </informalexample> - </para> - </listitem> - - <listitem> - <para> - Create the Kconfig entry - </para> - - <para> - Add the new entry of Kconfig for your xyz driver. - <informalexample> - <programlisting> -<![CDATA[ - config SND_XYZ - tristate "Foobar XYZ" - depends on SND - select SND_PCM - help - Say Y here to include support for Foobar XYZ soundcard. - - To compile this driver as a module, choose M here: the module - will be called snd-xyz. -]]> - </programlisting> - </informalexample> - - the line, select SND_PCM, specifies that the driver xyz supports - PCM. In addition to SND_PCM, the following components are - supported for select command: - SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART, - SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC. - Add the select command for each supported component. - </para> - - <para> - Note that some selections imply the lowlevel selections. - For example, PCM includes TIMER, MPU401_UART includes RAWMIDI, - AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP. - You don't need to give the lowlevel selections again. - </para> - - <para> - For the details of Kconfig script, refer to the kbuild - documentation. - </para> - - </listitem> - - <listitem> - <para> - Run cvscompile script to re-generate the configure script and - build the whole stuff again. - </para> - </listitem> - </orderedlist> - </para> - </section> - - <section> - <title>Drivers with Several Source Files</title> - <para> - Suppose that the driver snd-xyz have several source files. - They are located in the new subdirectory, - pci/xyz. - - <orderedlist> - <listitem> - <para> - Add a new directory (<filename>xyz</filename>) in - <filename>alsa-driver/pci/Makefile</filename> as below - - <informalexample> - <programlisting> -<![CDATA[ - obj-$(CONFIG_SND) += xyz/ -]]> - </programlisting> - </informalexample> - </para> - </listitem> - - <listitem> - <para> - Under the directory <filename>xyz</filename>, create a Makefile - - <example> - <title>Sample Makefile for a driver xyz</title> - <programlisting> -<![CDATA[ - ifndef SND_TOPDIR - SND_TOPDIR=../.. - endif - - include $(SND_TOPDIR)/toplevel.config - include $(SND_TOPDIR)/Makefile.conf - - snd-xyz-objs := xyz.o abc.o def.o - - obj-$(CONFIG_SND_XYZ) += snd-xyz.o - - include $(SND_TOPDIR)/Rules.make -]]> - </programlisting> - </example> - </para> - </listitem> - - <listitem> - <para> - Create the Kconfig entry - </para> - - <para> - This procedure is as same as in the last section. - </para> - </listitem> - - <listitem> - <para> - Run cvscompile script to re-generate the configure script and - build the whole stuff again. - </para> - </listitem> - </orderedlist> - </para> - </section> - - </chapter> - -<!-- ****************************************************** --> -<!-- Useful Functions --> -<!-- ****************************************************** --> - <chapter id="useful-functions"> - <title>Useful Functions</title> - - <section id="useful-functions-snd-printk"> - <title><function>snd_printk()</function> and friends</title> - <para> - ALSA provides a verbose version of the - <function>printk()</function> function. If a kernel config - <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this - function prints the given message together with the file name - and the line of the caller. The <constant>KERN_XXX</constant> - prefix is processed as - well as the original <function>printk()</function> does, so it's - recommended to add this prefix, e.g. - - <informalexample> - <programlisting> -<![CDATA[ - snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n"); -]]> - </programlisting> - </informalexample> - </para> - - <para> - There are also <function>printk()</function>'s for - debugging. <function>snd_printd()</function> can be used for - general debugging purposes. If - <constant>CONFIG_SND_DEBUG</constant> is set, this function is - compiled, and works just like - <function>snd_printk()</function>. If the ALSA is compiled - without the debugging flag, it's ignored. - </para> - - <para> - <function>snd_printdd()</function> is compiled in only when - <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note - that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default - even if you configure the alsa-driver with - <option>--with-debug=full</option> option. You need to give - explicitly <option>--with-debug=detect</option> option instead. - </para> - </section> - - <section id="useful-functions-snd-bug"> - <title><function>snd_BUG()</function></title> - <para> - It shows the <computeroutput>BUG?</computeroutput> message and - stack trace as well as <function>snd_BUG_ON</function> at the point. - It's useful to show that a fatal error happens there. - </para> - <para> - When no debug flag is set, this macro is ignored. - </para> - </section> - - <section id="useful-functions-snd-bug-on"> - <title><function>snd_BUG_ON()</function></title> - <para> - <function>snd_BUG_ON()</function> macro is similar with - <function>WARN_ON()</function> macro. For example, - - <informalexample> - <programlisting> -<![CDATA[ - snd_BUG_ON(!pointer); -]]> - </programlisting> - </informalexample> - - or it can be used as the condition, - <informalexample> - <programlisting> -<![CDATA[ - if (snd_BUG_ON(non_zero_is_bug)) - return -EINVAL; -]]> - </programlisting> - </informalexample> - - </para> - - <para> - The macro takes an conditional expression to evaluate. - When <constant>CONFIG_SND_DEBUG</constant>, is set, if the - expression is non-zero, it shows the warning message such as - <computeroutput>BUG? (xxx)</computeroutput> - normally followed by stack trace. - - In both cases it returns the evaluated value. - </para> - - </section> - - </chapter> - - -<!-- ****************************************************** --> -<!-- Acknowledgments --> -<!-- ****************************************************** --> - <chapter id="acknowledgments"> - <title>Acknowledgments</title> - <para> - I would like to thank Phil Kerr for his help for improvement and - corrections of this document. - </para> - <para> - Kevin Conder reformatted the original plain-text to the - DocBook format. - </para> - <para> - Giuliano Pochini corrected typos and contributed the example codes - in the hardware constraints section. - </para> - </chapter> -</book> |