From 7ddedebb03b7ec030c528ebacdd43e45373476e3 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 29 Sep 2016 18:21:46 +0200 Subject: ALSA: doc: ReSTize writing-an-alsa-driver document Another simple conversion from DocBook to ReST. This required a few manual fixups and reformats, but the most of contents are kept as is. Signed-off-by: Takashi Iwai --- Documentation/DocBook/Makefile | 3 +- Documentation/DocBook/writing-an-alsa-driver.tmpl | 6206 --------------------- 2 files changed, 1 insertion(+), 6208 deletions(-) delete mode 100644 Documentation/DocBook/writing-an-alsa-driver.tmpl (limited to 'Documentation/DocBook') diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index e173497959fa..72f78ae46c10 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -12,8 +12,7 @@ DOCBOOKS := z8530book.xml \ kernel-api.xml filesystems.xml lsm.xml usb.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 \ - 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/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 @@ - - - - - - - - - Writing an ALSA Driver - - Takashi - Iwai - -
- tiwai@suse.de -
- - - - Oct 15, 2007 - 0.3.7 - - - - This document describes how to write an ALSA (Advanced Linux - Sound Architecture) driver. - - - - - - Copyright (c) 2002-2005 Takashi Iwai tiwai@suse.de - - - - 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. - - - - This document is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the - implied warranty of MERCHANTABILITY or FITNESS FOR A - PARTICULAR PURPOSE. See the GNU General Public License - for more details. - - - - 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 - - - - - - - - - - Preface - - This document describes how to write an - - ALSA (Advanced Linux Sound Architecture) - 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. - - - - 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. - - - - If you are already familiar with the older ALSA ver.0.5.x API, you - can check the drivers such as sound/pci/es1938.c or - sound/pci/maestro3.c which have also almost the same - code-base in the ALSA 0.5.x tree, so you can compare the differences. - - - - This document is still a draft version. Any feedback and - corrections, please!! - - - - - - - - - File Tree Structure - -
- General - - The ALSA drivers are provided in two ways. - - - - 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. - - - - The file tree structure of ALSA driver is depicted below. Both - alsa-kernel and alsa-driver have almost the same file - structure, except for core directory. It's - named as acore in alsa-driver tree. - - - ALSA File Tree Structure - - 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 - - - -
- -
- core directory - - 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. - - -
- core/oss - - - 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 core/seq/oss directory (see - - below). - -
- -
- core/ioctl32 - - - 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. - -
- -
- core/seq - - 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 - CONFIG_SND_SEQUENCER is set in the kernel - config. - -
- -
- core/seq/oss - - This contains the OSS sequencer emulation codes. - -
- -
- core/seq/instr - - This directory contains the modules for the sequencer - instrument layer. - -
-
- -
- include directory - - 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 :) - -
- -
- drivers directory - - 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. - - -
- drivers/mpu401 - - The MPU401 and MPU401-UART modules are stored here. - -
- -
- drivers/opl3 and opl4 - - The OPL3 and OPL4 FM-synth stuff is found here. - -
-
- -
- i2c directory - - This contains the ALSA i2c components. - - - - 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. - - -
- i2c/l3 - - This is a sub-directory for ARM L3 i2c. - -
-
- -
- synth directory - - This contains the synth middle-level modules. - - - - So far, there is only Emu8000/Emu10k1 synth driver under - the synth/emux sub-directory. - -
- -
- pci directory - - This directory and its sub-directories hold the top-level card modules - for PCI soundcards and the code specific to the PCI BUS. - - - - 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). - -
- -
- isa directory - - This directory and its sub-directories hold the top-level card modules - for ISA soundcards. - -
- -
- arm, ppc, and sparc directories - - They are used for top-level card modules which are - specific to one of these architectures. - -
- -
- usb directory - - This directory contains the USB-audio driver. In the latest version, the - USB MIDI driver is integrated in the usb-audio driver. - -
- -
- pcmcia directory - - 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. - -
- -
- oss directory - - 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 :) - -
- - - - - - - - Basic Flow for PCI Drivers - -
- Outline - - The minimum flow for PCI soundcards is as follows: - - - define the PCI ID table (see the section - PCI Entries - ). - create probe() callback. - create remove() callback. - create a pci_driver structure - containing the three pointers above. - create an init() function just calling - the pci_register_driver() to register the pci_driver table - defined above. - create an exit() function to call - the pci_unregister_driver() function. - - -
- -
- Full Code Example - - 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 - snd_mychip_probe() function - refer to details explained in the following section. - - - Basic Flow for PCI Drivers - Example - - - #include - #include - #include - #include - - /* 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); - } -]]> - - - -
- -
- Constructor - - The real constructor of PCI drivers is the probe callback. - The probe callback and other component-constructors which are called - from the probe callback cannot be used with - the __init prefix - because any PCI device could be a hotplug device. - - - - In the probe callback, the following scheme is often used. - - -
- 1) Check and increment the device index. - - - -= SNDRV_CARDS) - return -ENODEV; - if (!enable[dev]) { - dev++; - return -ENOENT; - } -]]> - - - - where enable[dev] is the module option. - - - - Each time the probe 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 (step - 7). - -
- -
- 2) Create a card instance - - - -dev, index[dev], id[dev], THIS_MODULE, - 0, &card); -]]> - - - - - - The details will be explained in the section - - Management of Cards and Components. - -
- -
- 3) Create a main component - - In this part, the PCI resources are allocated. - - - - - - - - The details will be explained in the section PCI Resource - Management. - -
- -
- 4) Set the driver ID and name strings. - - - -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); -]]> - - - - 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. - - - - The shortname field is a string shown as more verbose - name. The longname field contains the information - shown in /proc/asound/cards. - -
- -
- 5) Create other components, such as mixer, MIDI, etc. - - Here you define the basic components such as - PCM, - mixer (e.g. AC97), - MIDI (e.g. MPU-401), - and other interfaces. - Also, if you want a proc - file, define it here, too. - -
- -
- 6) Register the card instance. - - - - - - - - - - Will be explained in the section Management - of Cards and Components, too. - -
- -
- 7) Set the PCI driver data and return zero. - - - - - - - - In the above, the card record is stored. This pointer is - used in the remove callback and power-management - callbacks, too. - -
-
- -
- Destructor - - The destructor, remove callback, simply releases the card - instance. Then the ALSA middle layer will release all the - attached components automatically. - - - - It would be typically like the following: - - - - - - - - The above code assumes that the card pointer is set to the PCI - driver data. - -
- -
- Header Files - - For the above example, at least the following include files - are necessary. - - - - - #include - #include - #include - #include -]]> - - - - 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. - - - - In addition to these headers, you'll need - <linux/interrupt.h> for interrupt - handling, and <asm/io.h> for I/O - access. If you use the mdelay() or - udelay() functions, you'll need to include - <linux/delay.h> too. - - - - The ALSA interfaces like the PCM and control APIs are defined in other - <sound/xxx.h> header files. - They have to be included after - <sound/core.h>. - - -
- - - - - - - - Management of Cards and Components - -
- Card Instance - - For each soundcard, a card record must be allocated. - - - - 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. - - - - As mentioned above, to create a card instance, call - snd_card_new(). - - - -dev, index, id, module, extra_size, &card); -]]> - - - - - - The function takes six arguments: the parent device pointer, - the card-index number, the id string, the module pointer (usually - THIS_MODULE), - 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 snd_card_new(). - - - - The first argument, the pointer of struct - device, specifies the parent device. - For PCI devices, typically &pci-> is passed there. - -
- -
- Components - - 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 snd_device object. - A component can be a PCM instance, a control interface, a raw - MIDI interface, etc. Each such instance has one component - entry. - - - - A component can be created via - snd_device_new() function. - - - - - - - - - - This takes the card pointer, the device-level - (SNDRV_DEV_XXX), the data pointer, and the - callback pointers (&ops). 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 SNDRV_DEV_LOWLEVEL. - - - - 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 (chip in the - above example) is used as the identifier for the instance. - - - - Each pre-defined ALSA component such as ac97 and pcm calls - snd_device_new() 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. - - - - If you wish to create your own component, you need to - set the destructor function to the dev_free callback in - the ops, so that it can be released - automatically via snd_card_free(). - The next example will show an implementation of chip-specific - data. - -
- -
- Chip-Specific Data - - Chip-specific information, e.g. the I/O port address, its - resource pointer, or the irq number, is stored in the - chip-specific record. - - - - - - - - - - In general, there are two ways of allocating the chip record. - - -
- 1. Allocating via <function>snd_card_new()</function>. - - As mentioned above, you can pass the extra-data-length - to the 5th argument of snd_card_new(), i.e. - - - -dev, index[dev], id[dev], THIS_MODULE, - sizeof(struct mychip), &card); -]]> - - - - struct mychip is the type of the chip record. - - - - In return, the allocated record can be accessed as - - - -private_data; -]]> - - - - With this method, you don't have to allocate twice. - The record is released together with the card instance. - -
- -
- 2. Allocating an extra device. - - - After allocating a card instance via - snd_card_new() (with - 0 on the 4th arg), call - kzalloc(). - - - -dev, index[dev], id[dev], THIS_MODULE, - 0, &card); - ..... - chip = kzalloc(sizeof(*chip), GFP_KERNEL); -]]> - - - - - - The chip record should have the field to hold the card - pointer at least, - - - - - - - - - - Then, set the card pointer in the returned chip instance. - - - -card = card; -]]> - - - - - - Next, initialize the fields, and register this chip - record as a low-level device with a specified - ops, - - - - - - - - snd_mychip_dev_free() is the - device-destructor function, which will call the real - destructor. - - - - - -device_data); - } -]]> - - - - where snd_mychip_free() is the real destructor. - -
-
- -
- Registration and Release - - After all components are assigned, register the card instance - by calling snd_card_register(). Access - to the device files is enabled at this point. That is, before - snd_card_register() is called, the - components are safely inaccessible from external side. If this - call fails, exit the probe function after releasing the card via - snd_card_free(). - - - - For releasing the card instance, you can call simply - snd_card_free(). As mentioned earlier, all - components are released automatically by this call. - - - - For a device which allows hotplugging, you can use - snd_card_free_when_closed. This one will - postpone the destruction until all devices are closed. - - -
- - - - - - - - - PCI Resource Management - -
- Full Code Example - - In this section, we'll complete the chip-specific constructor, - destructor and PCI entries. Example code is shown first, - below. - - - PCI Resource Management Example - -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 */ -]]> - - - -
- -
- Some Hafta's - - The allocation of PCI resources is done in the - probe() function, and usually an extra - xxx_create() function is written for this - purpose. - - - - In the case of PCI devices, you first have to call - the pci_enable_device() 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 pci_set_master() function, - too. - - - - Suppose the 28bit mask, and the code to be added would be like: - - - - - - - -
- -
- Resource Allocation - - 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. - - - - Now assume that the PCI device has an I/O port with 8 bytes - and an interrupt. Then struct mychip will have the - following fields: - - - - - - - - - - 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 - kzalloc() automatically, so you - don't have to take care of resetting them. - - - - The allocation of an I/O port is done like this: - - - -port = pci_resource_start(pci, 0); -]]> - - - - - - - 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 kmalloc() by - request_region(). The pointer must be - released via kfree(), but there is a - problem with this. This issue will be explained later. - - - - The allocation of an interrupt source is done like this: - - - -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; -]]> - - - - where snd_mychip_interrupt() is the - interrupt handler defined later. - Note that chip->irq should be defined - only when request_irq() succeeded. - - - - On the PCI bus, interrupts can be shared. Thus, - IRQF_SHARED is used as the interrupt flag of - request_irq(). - - - - The last argument of request_irq() 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. - - - - 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: - - - - - - - - - - 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. - - - - To release the resources, the check-and-release - method is a safer way. For the interrupt, do like this: - - - -irq >= 0) - free_irq(chip->irq, chip); -]]> - - - - 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. - - - - When you requested I/O ports or memory regions via - pci_request_region() or - pci_request_regions() like in this example, - release the resource(s) using the corresponding function, - pci_release_region() or - pci_release_regions(). - - - -pci); -]]> - - - - - - When you requested manually via request_region() - or request_mem_region, you can release it via - release_resource(). Suppose that you keep - the resource pointer returned from request_region() - in chip->res_port, the release procedure looks like: - - - -res_port); -]]> - - - - - - Don't forget to call pci_disable_device() - before the end. - - - - And finally, release the chip-specific record. - - - - - - - - - - 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. - - - - When the chip-data is assigned to the card using - snd_device_new() with - SNDRV_DEV_LOWLELVEL , 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. - - - - 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: - - - - - - - - and the allocation would be like below: - - - -iobase_phys = pci_resource_start(pci, 0); - chip->iobase_virt = ioremap_nocache(chip->iobase_phys, - pci_resource_len(pci, 0)); -]]> - - - - and the corresponding destructor would be: - - - -iobase_virt) - iounmap(chip->iobase_virt); - .... - pci_release_regions(chip->pci); - .... - } -]]> - - - - -
- -
- PCI Entries - - So far, so good. Let's finish the missing PCI - stuff. At first, we need a - pci_device_id table for this - chipset. It's a table of PCI vendor/device ID number, and some - masks. - - - - For example, - - - - - - - - - - The first and second fields of - the pci_device_id 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 pci_device_id 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. - - - - The last entry of this list is the terminator. You must - specify this all-zero entry. - - - - Then, prepare the pci_driver record: - - - - - - - - - - The probe and - remove functions have already - been defined in the previous sections. - The name - field is the name string of this device. Note that you must not - use a slash / in this string. - - - - And at last, the module entries: - - - - - - - - - - Note that these module entries are tagged with - __init and - __exit prefixes. - - - - 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). - - - - - - - - That's all! - -
- - - - - - - - PCM Interface - -
- General - - 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. - - - - For accessing to the PCM layer, you need to include - <sound/pcm.h> first. In addition, - <sound/pcm_params.h> might be needed - if you access to some functions related with hw_param. - - - - 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. - - - - 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 EAGAIN 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. - -
- -
- Full Code Example - - The example code below does not include any hardware access - routines but shows only the skeleton, how to build up the PCM - interfaces. - - - PCM Example Code - - - .... - - /* 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; - } -]]> - - - -
- -
- Constructor - - A pcm instance is allocated by the snd_pcm_new() - function. It would be better to create a constructor for pcm, - namely, - - - -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; - } -]]> - - - - - - The snd_pcm_new() function takes four - arguments. The first argument is the card pointer to which this - pcm is assigned, and the second is the ID string. - - - - The third argument (index, 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, - index = 1 for the second PCM device. - - - - 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. - - - - 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 snd_pcm_substream data passed to each callback - as follows: - - - -number; -]]> - - - - - - After the pcm is created, you need to set operators for each - pcm stream. - - - - - - - - - - The operators are defined typically like this: - - - - - - - - All the callbacks are described in the - - Operators subsection. - - - - After setting the operators, you probably will want to - pre-allocate the buffer. For the pre-allocation, simply call - the following: - - - -pci), - 64*1024, 64*1024); -]]> - - - - It will allocate a buffer up to 64kB as default. - Buffer management details will be described in the later section Buffer and Memory - Management. - - - - Additionally, you can set some extra information for this pcm - in pcm->info_flags. - The available values are defined as - SNDRV_PCM_INFO_XXX in - <sound/asound.h>, which is used for - the hardware definition (described later). When your soundchip - supports only half-duplex, specify like this: - - - -info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; -]]> - - - -
- -
- ... And the Destructor? - - 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. - - - - 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: - - - PCM Instance with a Destructor - -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; - .... - } -]]> - - - -
- -
- Runtime Pointer - The Chest of PCM Information - - When the PCM substream is opened, a PCM runtime instance is - allocated and assigned to the substream. This pointer is - accessible via substream->runtime. - 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. - - - - The definition of runtime instance is found in - <sound/pcm.h>. Here are - the contents of this file: - - - - - - - - - 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 snd_pcm_lib_malloc_pages(), - you don't need to set the DMA buffer information by yourself. - - - - In the sections below, important records are explained. - - -
- Hardware Description - - The hardware descriptor (struct snd_pcm_hardware) - contains the definitions of the fundamental hardware - configuration. Above all, you'll need to define this in - - the open callback. - 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 - (runtime->hw) 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: - - -runtime; - ... - runtime->hw = snd_mychip_playback_hw; /* common definition */ - if (chip->model == VERY_OLD_ONE) - runtime->hw.channels_max = 1; -]]> - - - - - - Typically, you'll have a hardware descriptor as below: - - - - - - - - - - - The info field contains the type and - capabilities of this pcm. The bit flags are defined in - <sound/asound.h> as - SNDRV_PCM_INFO_XXX. 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 - SNDRV_PCM_INFO_MMAP flag here. When the - hardware supports the interleaved or the non-interleaved - formats, SNDRV_PCM_INFO_INTERLEAVED or - SNDRV_PCM_INFO_NONINTERLEAVED flag must - be set, respectively. If both are supported, you can set both, - too. - - - - In the above example, MMAP_VALID and - BLOCK_TRANSFER are specified for the OSS mmap - mode. Usually both are set. Of course, - MMAP_VALID is set only if the mmap is - really supported. - - - - The other possible flags are - SNDRV_PCM_INFO_PAUSE and - SNDRV_PCM_INFO_RESUME. The - PAUSE bit means that the pcm supports the - pause operation, while the - RESUME bit means that the pcm supports - the full suspend/resume operation. - If the PAUSE flag is set, - the trigger callback below - must handle the corresponding (pause push/release) commands. - The suspend/resume trigger commands can be defined even without - the RESUME flag. See - Power Management section for details. - - - - When the PCM substreams can be synchronized (typically, - synchronized start/stop of a playback and a capture streams), - you can give SNDRV_PCM_INFO_SYNC_START, - 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. - - - - - - formats field contains the bit-flags - of supported formats (SNDRV_PCM_FMTBIT_XXX). - 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. - - - - - - rates field contains the bit-flags of - supported rates (SNDRV_PCM_RATE_XXX). - When the chip supports continuous rates, pass - CONTINUOUS bit additionally. - The pre-defined rate bits are provided only for typical - rates. If your chip supports unconventional rates, you need to add - the KNOT bit and set up the hardware - constraint manually (explained later). - - - - - - rate_min and - rate_max define the minimum and - maximum sample rate. This should correspond somehow to - rates bits. - - - - - - channel_min and - channel_max - define, as you might already expected, the minimum and maximum - number of channels. - - - - - - buffer_bytes_max defines the - maximum buffer size in bytes. There is no - buffer_bytes_min field, since - it can be calculated from the minimum period size and the - minimum number of periods. - Meanwhile, period_bytes_min and - define the minimum and maximum size of the period in bytes. - periods_max and - periods_min define the maximum and - minimum number of periods in the buffer. - - - - The period 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. - - - - - - There is also a field fifo_size. - 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. - - - - -
- -
- PCM Configurations - - 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 hw_params data via - alsa-lib. There are many fields copied from hw_params and - sw_params structs. For example, - format holds the format type - chosen by the application. This field contains the enum value - SNDRV_PCM_FORMAT_XXX. - - - - One thing to be noted is that the configured buffer and period - sizes are stored in frames in the runtime. - In the ALSA world, 1 frame = channels * samples-size. - For conversion between frames and bytes, you can use the - frames_to_bytes() and - bytes_to_frames() helper functions. - - -period_size); -]]> - - - - - - Also, many software parameters (sw_params) are - stored in frames, too. Please check the type of the field. - snd_pcm_uframes_t is for the frames as unsigned - integer while snd_pcm_sframes_t is for the frames - as signed integer. - -
- -
- DMA Buffer Information - - The DMA buffer is defined by the following four fields, - dma_area, - dma_addr, - dma_bytes and - dma_private. - The dma_area holds the buffer - pointer (the logical address). You can call - memcpy from/to - this pointer. Meanwhile, dma_addr - holds the physical address of the buffer. This field is - specified only when the buffer is a linear buffer. - dma_bytes holds the size of buffer - in bytes. dma_private is used for - the ALSA DMA allocator. - - - - If you use a standard ALSA function, - snd_pcm_lib_malloc_pages(), for - allocating the buffer, these fields are set by the ALSA middle - layer, and you should not 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, dma_bytes is mandatory. - dma_area is necessary when the - buffer is mmapped. If your driver doesn't support mmap, this - field is not necessary. dma_addr - is also optional. You can use - dma_private as you like, too. - -
- -
- Running Status - - The running status can be referred via runtime->status. - This is the pointer to the struct snd_pcm_mmap_status - record. For example, you can get the current DMA hardware - pointer via runtime->status->hw_ptr. - - - - The DMA application pointer can be referred via - runtime->control, which points to the - struct snd_pcm_mmap_control record. - However, accessing directly to this value is not recommended. - -
- -
- Private Data - - You can allocate a record for the substream and store it in - runtime->private_data. Usually, this - is done in - - the open callback. - Don't mix this with pcm->private_data. - The pcm->private_data usually points to the - chip instance assigned statically at the creation of PCM, while the - runtime->private_data points to a dynamic - data structure created at the PCM open callback. - - - -runtime->private_data = data; - .... - } -]]> - - - - - - The allocated object must be released in - - the close callback. - -
- -
- -
- Operators - - OK, now let me give details about each pcm callback - (ops). In general, every callback must - return 0 if successful, or a negative error number - such as -EINVAL. 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. - - - - The callback function takes at least the argument with - snd_pcm_substream pointer. To retrieve - the chip record from the given substream instance, you can use the - following macro. - - - - - - - - The macro reads substream->private_data, - which is a copy of pcm->private_data. - 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. - - -
- open callback - - - - - - - - This is called when a pcm substream is opened. - - - - At least, here you have to initialize the runtime->hw - record. Typically, this is done by like this: - - - -runtime; - - runtime->hw = snd_mychip_playback_hw; - return 0; - } -]]> - - - - where snd_mychip_playback_hw is the - pre-defined hardware description. - - - - You can allocate a private data in this callback, as described - in - Private Data section. - - - - If the hardware configuration needs more constraints, set the - hardware constraints here, too. - See - Constraints for more details. - -
- -
- close callback - - - - - - - - Obviously, this is called when a pcm substream is closed. - - - - Any private instance for a pcm substream allocated in the - open callback will be released here. - - - -runtime->private_data); - .... - } -]]> - - - -
- -
- ioctl callback - - This is used for any special call to pcm ioctls. But - usually you can pass a generic ioctl callback, - snd_pcm_lib_ioctl. - -
- -
- hw_params callback - - - - - - - - - - This is called when the hardware parameter - (hw_params) 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. - - - - Many hardware setups should be done in this callback, - including the allocation of buffers. - - - - Parameters to be initialized are retrieved by - params_xxx() macros. To allocate - buffer, you can call a helper function, - - - - - - - - snd_pcm_lib_malloc_pages() is available - only when the DMA buffers have been pre-allocated. - See the section - Buffer Types for more details. - - - - Note that this and prepare callbacks - may be called multiple times per initialization. - For example, the OSS emulation may - call these callbacks at each change via its ioctl. - - - - 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. - - - - Another note is that this callback is non-atomic - (schedulable) as default, i.e. when no - nonatomic flag set. - This is important, because the - trigger callback - is atomic (non-schedulable). That is, mutexes or any - schedule-related functions are not available in - trigger callback. - Please see the subsection - - Atomicity for details. - -
- -
- hw_free callback - - - - - - - - - - This is called to release the resources allocated via - hw_params. For example, releasing the - buffer via - snd_pcm_lib_malloc_pages() is done by - calling the following: - - - - - - - - - - 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. - -
- -
- prepare callback - - - - - - - - - - This callback is called when the pcm is - prepared. You can set the format type, sample - rate, etc. here. The difference from - hw_params is that the - prepare callback will be called each - time - snd_pcm_prepare() is called, i.e. when - recovering after underruns, etc. - - - - Note that this callback is now non-atomic. - You can use schedule-related functions safely in this callback. - - - - 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. - - - - Be careful that this callback will be called many times at - each setup, too. - -
- -
- trigger callback - - - - - - - - This is called when the pcm is started, stopped or paused. - - - - Which action is specified in the second argument, - SNDRV_PCM_TRIGGER_XXX in - <sound/pcm.h>. At least, - the START and STOP - commands must be defined in this callback. - - - - - - - - - - When the pcm supports the pause operation (given in the info - field of the hardware table), the PAUSE_PUSH - and PAUSE_RELEASE commands must be - handled here, too. The former is the command to pause the pcm, - and the latter to restart the pcm again. - - - - When the pcm supports the suspend/resume operation, - regardless of full or partial suspend/resume support, - the SUSPEND and RESUME - commands must be handled, too. - These commands are issued when the power-management status is - changed. Obviously, the SUSPEND and - RESUME commands - suspend and resume the pcm substream, and usually, they - are identical to the STOP and - START commands, respectively. - See the - Power Management section for details. - - - - As mentioned, this callback is atomic as default unless - nonatomic 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. - -
- -
- pointer callback - - - - - - - - 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. - - - - This is called usually from the buffer-update routine in the - pcm middle layer, which is invoked when - snd_pcm_period_elapsed() 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. - - - - This callback is also atomic as default. - -
- -
- copy and silence callbacks - - 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. - - - - If these two callbacks are defined, copy and set-silence - operations are done by them. The detailed will be described in - the later section Buffer and Memory - Management. - -
- -
- ack callback - - 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. - - - This callback is atomic as default. - -
- -
- page callback - - - 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 Buffer and Memory - Management, too. - -
-
- -
- Interrupt Handler - - 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 snd_pcm_period_elapsed() - function. - - - - There are several types of sound chips to generate the interrupts. - - -
- Interrupts at the period (fragment) boundary - - This is the most frequently found type: the hardware - generates an interrupt at each period boundary. - In this case, you can call - snd_pcm_period_elapsed() at each - interrupt. - - - - snd_pcm_period_elapsed() 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). - - - - 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 - snd_pcm_period_elapsed(), because - snd_pcm_period_elapsed() calls other pcm - callbacks inside. - - - - Typical code would be like: - - - Interrupt Handler Case #1 - -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; - } -]]> - - - -
- -
- High frequency timer interrupts - - 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 - snd_pcm_period_elapsed() and reset the - accumulator. - - - - Typical code would be like the following. - - - Interrupt Handler Case #2 - -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; - } -]]> - - - -
- -
- On calling <function>snd_pcm_period_elapsed()</function> - - In both cases, even if more than one period are elapsed, you - don't have to call - snd_pcm_period_elapsed() many times. Call - only once. And the pcm layer will check the current hardware - pointer and update to the latest status. - -
-
- -
- Atomicity - - 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. - - - - As already seen, some pcm callbacks are atomic and some are - not. For example, the hw_params callback is - non-atomic, while trigger 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. - - - - In the atomic callbacks, you cannot use functions which may call - schedule or go to - sleep. Semaphores and mutexes can sleep, - and hence they cannot be used inside the atomic callbacks - (e.g. trigger callback). - To implement some delay in such a callback, please use - udelay() or mdelay(). - - - - All three atomic callbacks (trigger, pointer, and ack) are - called with local interrupts disabled. - - - - 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 - snd_pcm_period_elapsed() 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 - nonatomic filed of - snd_pcm 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. - - -
-
- Constraints - - If your chip supports unconventional sample rates, or only the - limited samples, you need to set a constraint for the - condition. - - - - For example, in order to restrict the sample rates in the some - supported values, use - snd_pcm_hw_constraint_list(). - You need to call this function in the open callback. - - - Example of Hardware Constraints - -runtime, 0, - SNDRV_PCM_HW_PARAM_RATE, - &constraints_rates); - if (err < 0) - return err; - .... - } -]]> - - - - - - There are many different constraints. - Look at sound/pcm.h 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 snd_pcm_hardware structure (or in any - other constraint_list). You can build a rule like this: - - - Example of Hardware Constraints for Channels - -bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { - ch.min = ch.max = 1; - ch.integer = 1; - return snd_interval_refine(c, &ch); - } - return 0; - } -]]> - - - - - - Then you need to call this function to add your rule: - - - -runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, - hw_rule_channels_by_format, NULL, - SNDRV_PCM_HW_PARAM_FORMAT, -1); -]]> - - - - - - 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 of Hardware Constraints for Formats - -min < 2) { - fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; - return snd_mask_refine(f, &fmt); - } - return 0; - } -]]> - - - - - - ...and in the open callback: - - -runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, - hw_rule_format_by_channels, NULL, - SNDRV_PCM_HW_PARAM_CHANNELS, -1); -]]> - - - - - - I won't give more details here, rather I - would like to say, Luke, use the source. - -
- - - - - - - - - Control Interface - -
- General - - 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. - - - - ALSA has a well-defined AC97 control module. If your chip - supports only the AC97 and nothing else, you can skip this - section. - - - - The control API is defined in - <sound/control.h>. - Include this file if you want to add your own controls. - -
- -
- Definition of Controls - - To create a new control, you need to define the - following three - callbacks: info, - get and - put. Then, define a - struct snd_kcontrol_new record, such as: - - - Definition of a Control - - - - - - - - The iface field specifies the control - type, SNDRV_CTL_ELEM_IFACE_XXX, which - is usually MIXER. - Use CARD 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 HWDEP, - PCM, RAWMIDI, - TIMER, or SEQUENCER, and - specify the device number with the - device and - subdevice fields. - - - - The name 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 - Control Names subsection. - - - - The index 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. - - - - The access field contains the access - type of this control. Give the combination of bit masks, - SNDRV_CTL_ELEM_ACCESS_XXX, there. - The details will be explained in - the - Access Flags subsection. - - - - The private_value field contains - an arbitrary long integer value for this record. When using - the generic info, - get and - put 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. - - - - The tlv field can be used to provide - metadata about the control; see the - - Metadata subsection. - - - - The other three are - - callback functions. - -
- -
- Control Names - - There are some standards to define the control names. A - control is usually defined from the three parts as - SOURCE DIRECTION FUNCTION. - - - - The first, SOURCE, specifies the source - of the control, and is a string such as Master, - PCM, CD and - Line. There are many pre-defined sources. - - - - The second, DIRECTION, is one of the - following strings according to the direction of the control: - Playback, Capture, Bypass - Playback and Bypass Capture. Or, it can - be omitted, meaning both playback and capture directions. - - - - The third, FUNCTION, is one of the - following strings according to the function of the control: - Switch, Volume and - Route. - - - - The example of control names are, thus, Master Capture - Switch or PCM Playback Volume. - - - - There are some exceptions: - - -
- Global capture and playback - - Capture Source, Capture Switch - and Capture Volume are used for the global - capture (input) source, switch and volume. Similarly, - Playback Switch and Playback - Volume are used for the global output gain switch and - volume. - -
- -
- Tone-controls - - tone-control switch and volumes are specified like - Tone Control - XXX, e.g. Tone Control - - Switch, Tone Control - Bass, - Tone Control - Center. - -
- -
- 3D controls - - 3D-control switches and volumes are specified like 3D - Control - XXX, e.g. 3D Control - - Switch, 3D Control - Center, 3D - Control - Space. - -
- -
- Mic boost - - Mic-boost switch is set as Mic Boost or - Mic Boost (6dB). - - - - More precise information can be found in - Documentation/sound/alsa/ControlNames.txt. - -
-
- -
- Access Flags - - - The access flag is the bitmask which specifies the access type - of the given control. The default access type is - SNDRV_CTL_ELEM_ACCESS_READWRITE, - which means both read and write are allowed to this control. - When the access flag is omitted (i.e. = 0), it is - considered as READWRITE access as default. - - - - When the control is read-only, pass - SNDRV_CTL_ELEM_ACCESS_READ instead. - In this case, you don't have to define - the put callback. - Similarly, when the control is write-only (although it's a rare - case), you can use the WRITE flag instead, and - you don't need the get callback. - - - - If the control value changes frequently (e.g. the VU meter), - VOLATILE flag should be given. This means - that the control may be changed without - - notification. Applications should poll such - a control constantly. - - - - When the control is inactive, set - the INACTIVE flag, too. - There are LOCK and - OWNER flags to change the write - permissions. - - -
- -
- Callbacks - -
- info callback - - The info callback is used to get - detailed information on this control. This must store the - values of the given struct snd_ctl_elem_info - object. For example, for a boolean control with a single - element: - - - Example of info callback - -type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; - uinfo->count = 1; - uinfo->value.integer.min = 0; - uinfo->value.integer.max = 1; - return 0; - } -]]> - - - - - - The type field specifies the type - of the control. There are BOOLEAN, - INTEGER, ENUMERATED, - BYTES, IEC958 and - INTEGER64. The - count field specifies the - number of elements in this control. For example, a stereo - volume would have count = 2. The - value field is a union, and - the values stored are depending on the type. The boolean and - integer types are identical. - - - - The enumerated type is a bit different from others. You'll - need to set the string for the currently given item index. - - - -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; - } -]]> - - - - - - The above callback can be simplified with a helper function, - snd_ctl_enum_info. 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.) - - - - - - - - - - Some common info callbacks are available for your convenience: - snd_ctl_boolean_mono_info() and - snd_ctl_boolean_stereo_info(). - Obviously, the former is an info callback for a mono channel - boolean item, just like snd_myctl_mono_info - above, and the latter is for a stereo channel boolean item. - - -
- -
- get callback - - - This callback is used to read the current value of the - control and to return to user-space. - - - - For example, - - - Example of get callback - -value.integer.value[0] = get_some_value(chip); - return 0; - } -]]> - - - - - - The value 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 - private_value field is set as follows: - - - - - - and is retrieved in callbacks like - - -private_value & 0xff; - int shift = (kcontrol->private_value >> 16) & 0xff; - int mask = (kcontrol->private_value >> 24) & 0xff; - .... - } -]]> - - - - - - In the get callback, - you have to fill all the elements if the - control has more than one elements, - i.e. count > 1. - In the example above, we filled only one element - (value.integer.value[0]) since it's - assumed as count = 1. - -
- -
- put callback - - - This callback is used to write a value from user-space. - - - - For example, - - - Example of put callback - -current_value != - ucontrol->value.integer.value[0]) { - change_current_value(chip, - ucontrol->value.integer.value[0]); - changed = 1; - } - return changed; - } -]]> - - - - 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. - - - - As in the get callback, - when the control has more than one elements, - all elements must be evaluated in this callback, too. - -
- -
- Callbacks are not atomic - - All these three callbacks are basically not atomic. - -
-
- -
- Constructor - - When everything is ready, finally we can create a new - control. To create a control, there are two functions to be - called, snd_ctl_new1() and - snd_ctl_add(). - - - - In the simplest way, you can do like this: - - - - - - - - where my_control is the - struct snd_kcontrol_new object defined above, and chip - is the object pointer to be passed to - kcontrol->private_data - which can be referred to in callbacks. - - - - snd_ctl_new1() allocates a new - snd_kcontrol instance, - and snd_ctl_add assigns the given - control component to the card. - -
- -
- Change Notification - - If you need to change and update a control in the interrupt - routine, you can call snd_ctl_notify(). For - example, - - - - - - - - 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 snd_ctl_elem_id - to be notified. - You can find some examples in es1938.c or - es1968.c for hardware volume interrupts. - -
- -
- Metadata - - To provide information about the dB values of a mixer control, use - on of the DECLARE_TLV_xxx macros from - <sound/tlv.h> to define a variable - containing this information, set thetlv.p - field to point to this variable, and include the - SNDRV_CTL_ELEM_ACCESS_TLV_READ flag in the - access field; like this: - - - - - - - - - The DECLARE_TLV_DB_SCALE 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. - - - - The DECLARE_TLV_DB_LINEAR 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 - TLV_DB_GAIN_MUTE. - -
- - - - - - - - - API for AC97 Codec - -
- General - - 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 - <sound/ac97_codec.h>. - -
- -
- Full Code Example - - - Example of AC97 Interface - -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); - } - -]]> - - - -
- -
- Constructor - - To create an ac97 instance, first call snd_ac97_bus - with an ac97_bus_ops_t record with callback functions. - - - - - - - - The bus record is shared among all belonging ac97 instances. - - - - And then call snd_ac97_mixer() with an - struct snd_ac97_template - record together with the bus pointer created above. - - - -ac97); -]]> - - - - where chip->ac97 is a pointer to a newly created - ac97_t 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. - -
- -
- Callbacks - - The standard callbacks are read and - write. Obviously they - correspond to the functions for read and write accesses to the - hardware low-level codes. - - - - The read callback returns the - register value specified in the argument. - - - -private_data; - .... - return the_register_value; - } -]]> - - - - Here, the chip can be cast from ac97->private_data. - - - - Meanwhile, the write callback is - used to set the register value. - - - - - - - - - - These callbacks are non-atomic like the control API callbacks. - - - - There are also other callbacks: - reset, - wait and - init. - - - - The reset callback is used to reset - the codec. If the chip requires a special kind of reset, you can - define this callback. - - - - The wait 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. - - - - The init callback is used for - additional initialization of the codec. - -
- -
- Updating Registers in The Driver - - If you need to access to the codec from the driver, you can - call the following functions: - snd_ac97_write(), - snd_ac97_read(), - snd_ac97_update() and - snd_ac97_update_bits(). - - - - Both snd_ac97_write() and - snd_ac97_update() functions are used to - set a value to the given register - (AC97_XXX). The difference between them is - that snd_ac97_update() doesn't write a - value if the given value has been already set, while - snd_ac97_write() always rewrites the - value. - - - - - - - - - - snd_ac97_read() is used to read the value - of the given register. For example, - - - - - - - - - - snd_ac97_update_bits() is used to update - some bits in the given register. - - - - - - - - - - Also, there is a function to change the sample rate (of a - given register such as - AC97_PCM_FRONT_DAC_RATE) when VRA or - DRA is supported by the codec: - snd_ac97_set_rate(). - - - - - - - - - - The following registers are available to set the rate: - AC97_PCM_MIC_ADC_RATE, - AC97_PCM_FRONT_DAC_RATE, - AC97_PCM_LR_ADC_RATE, - AC97_SPDIF. When - AC97_SPDIF is specified, the register is - not really changed but the corresponding IEC958 status bits will - be updated. - -
- -
- Clock Adjustment - - 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. - -
- -
- Proc Files - - The ALSA AC97 interface will create a proc file such as - /proc/asound/card0/codec97#0/ac97#0-0 and - ac97#0-0+regs. You can refer to these files to - see the current status and registers of the codec. - -
- -
- Multiple Codecs - - When there are several codecs on the same card, you need to - call snd_ac97_mixer() multiple times with - ac97.num=1 or greater. The num field - specifies the codec number. - - - - If you set up multiple codecs, you either need to write - different callbacks for each codec or check - ac97->num in the callback routines. - -
- - - - - - - - - MIDI (MPU401-UART) Interface - -
- General - - 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 - <sound/mpu401.h>. - - - - Some soundchips have a similar but slightly different - implementation of mpu401 stuff. For example, emu10k1 has its own - mpu401 routines. - -
- -
- Constructor - - To create a rawmidi object, call - snd_mpu401_uart_new(). - - - - - - - - - - The first argument is the card pointer, and the second is the - index of this component. You can create up to 8 rawmidi - devices. - - - - The third argument is the type of the hardware, - MPU401_HW_XXX. If it's not a special one, - you can use MPU401_HW_MPU401. - - - - 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. - - - - 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 - MPU401_INFO_INTEGRATED, - and the mpu401-uart layer will allocate the I/O ports by itself. - - - - When the controller supports only the input or output MIDI stream, - pass the MPU401_INFO_INPUT or - MPU401_INFO_OUTPUT bitflag, respectively. - Then the rawmidi instance is created as a single stream. - - - - MPU401_INFO_MMIO 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 snd_mpu401_uart_new(). - - - - When MPU401_INFO_TX_IRQ is set, the output - stream isn't checked in the default interrupt handler. The driver - needs to call snd_mpu401_uart_interrupt_tx() - by itself to start processing the output stream in the irq handler. - - - - If the MPU-401 interface shares its interrupt with the other logical - devices on the card, set MPU401_INFO_IRQ_HOOK - (see - below). - - - - Usually, the port address corresponds to the command port and - port + 1 corresponds to the data port. If not, you may change - the cport field of - struct snd_mpu401 manually - afterward. However, snd_mpu401 pointer is not - returned explicitly by - snd_mpu401_uart_new(). You need to cast - rmidi->private_data to - snd_mpu401 explicitly, - - - -private_data; -]]> - - - - and reset the cport as you like: - - - -cport = my_own_control_port; -]]> - - - - - - 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. - -
- -
- Interrupt Handler - - When the interrupt is allocated in - snd_mpu401_uart_new(), 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 MPU401_INFO_IRQ_HOOK, and call - snd_mpu401_uart_interrupt() explicitly from your - own interrupt handler when it has determined that a UART interrupt - has occurred. - - - - In this case, you need to pass the private_data of the - returned rawmidi object from - snd_mpu401_uart_new() as the second - argument of snd_mpu401_uart_interrupt(). - - - -private_data, regs); -]]> - - - -
- - - - - - - - - RawMIDI Interface - -
- Overview - - - 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. - - - - 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. - - - - The rawmidi API is defined in - <sound/rawmidi.h>. - -
- -
- Constructor - - - To create a rawmidi device, call the - snd_rawmidi_new function: - - -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; -]]> - - - - - - The first argument is the card pointer, the second argument is - the ID string. - - - - The third argument is the index of this component. You can - create up to 8 rawmidi devices. - - - - 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). - - - - Set the info_flags field to specify - the capabilities of the device. - Set SNDRV_RAWMIDI_INFO_OUTPUT if there is - at least one output port, - SNDRV_RAWMIDI_INFO_INPUT if there is at - least one input port, - and SNDRV_RAWMIDI_INFO_DUPLEX if the device - can handle output and input at the same time. - - - - 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: - - - - - - - - - The operators are usually defined like this: - - - - - - These callbacks are explained in the Callbacks - section. - - - - If there are more than one substream, you should give a - unique name to each of them: - - -streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams, - list { - sprintf(substream->name, "My MIDI Port %d", substream->number + 1); - } - /* same for SNDRV_RAWMIDI_STREAM_INPUT */ -]]> - - - -
- -
- Callbacks - - - In all the callbacks, the private data that you've set for the - rawmidi device can be accessed as - substream->rmidi->private_data. - - - - - 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: - - -number; -]]> - - - - -
- <function>open</function> callback - - - - - - - - - This is called when a substream is opened. - You can initialize the hardware here, but you shouldn't - start transmitting/receiving data yet. - -
- -
- <function>close</function> callback - - - - - - - - - Guess what. - - - - The open and close - callbacks of a rawmidi device are serialized with a mutex, - and can sleep. - -
- -
- <function>trigger</function> callback for output - substreams - - - - - - - - - This is called with a nonzero up - parameter when there is some data in the substream buffer that - must be transmitted. - - - - To read data from the buffer, call - snd_rawmidi_transmit_peek. 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 - snd_rawmidi_transmit_ack to remove the - data from the substream buffer: - - - - - - - - - If you know beforehand that the hardware will accept data, you - can use the snd_rawmidi_transmit function - which reads some data and removes them from the buffer at once: - - - - - - - - - If you know beforehand how many bytes you can accept, you can - use a buffer size greater than one with the - snd_rawmidi_transmit* functions. - - - - The trigger 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. - - - - The trigger callback is called with a - zero up parameter when the transmission - of data should be aborted. - -
- -
- <function>trigger</function> callback for input - substreams - - - - - - - - - This is called with a nonzero up - parameter to enable receiving data, or with a zero - up parameter do disable receiving data. - - - - The trigger callback must not sleep; the - actual reading of data from the device is usually done in an - interrupt handler. - - - - When data reception is enabled, your interrupt handler should - call snd_rawmidi_receive for all received - data: - - - - - - -
- -
- <function>drain</function> callback - - - - - - - - - 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. - - - - This callback is optional. If you do not set - drain in the struct snd_rawmidi_ops - structure, ALSA will simply wait for 50 milliseconds - instead. - -
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- - - - - - - - - Miscellaneous Devices - -
- FM OPL3 - - 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 - <sound/opl3.h>. - - - - FM registers can be directly accessed through the direct-FM API, - defined in <sound/asound_fm.h>. 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 /dev/dmfmX device. - - - - To create the OPL3 component, you have two functions to - call. The first one is a constructor for the opl3_t - instance. - - - - - - - - - - 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. - - - - The fourth argument is the hardware type. - - - - When the left and right ports have been already allocated by - the card driver, pass non-zero to the fifth argument - (integrated). Otherwise, the opl3 module will - allocate the specified ports by itself. - - - - When the accessing the hardware requires special method - instead of the standard I/O access, you can create opl3 instance - separately with snd_opl3_new(). - - - - - - - - - - Then set command, - private_data and - private_free 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. - - - - After creating the opl3 instance via snd_opl3_new(), - call snd_opl3_init() to initialize the chip to the - proper state. Note that snd_opl3_create() always - calls it internally. - - - - If the opl3 instance is created successfully, then create a - hwdep device for this opl3. - - - - - - - - - - The first argument is the opl3_t instance you - created, and the second is the index number, usually 0. - - - - 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). - -
- -
- Hardware-Dependent Devices - - 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 <sound/hwdep.h>. You can - find examples in opl3 driver or - isa/sb/sb16_csp.c. - - - - The creation of the hwdep instance is done via - snd_hwdep_new(). - - - - - - - - where the third argument is the index number. - - - - You can then pass any pointer value to the - private_data. - If you assign a private data, you should define the - destructor, too. The destructor function is set in - the private_free field. - - - -private_data = p; - hw->private_free = mydata_free; -]]> - - - - and the implementation of the destructor would be: - - - -private_data; - kfree(p); - } -]]> - - - - - - The arbitrary file operations can be defined for this - instance. The file operators are defined in - the ops table. For example, assume that - this chip needs an ioctl. - - - -ops.open = mydata_open; - hw->ops.ioctl = mydata_ioctl; - hw->ops.release = mydata_release; -]]> - - - - And implement the callback functions as you like. - -
- -
- IEC958 (S/PDIF) - - Usually the controls for IEC958 devices are implemented via - the control interface. There is a macro to compose a name string for - IEC958 controls, SNDRV_CTL_NAME_IEC958() - defined in <include/asound.h>. - - - - There are some standard controls for IEC958 status bits. These - controls use the type SNDRV_CTL_ELEM_TYPE_IEC958, - and the size of element is fixed as 4 bytes array - (value.iec958.status[x]). For the info - callback, you don't specify - the value field for this type (the count field must be set, - though). - - - - IEC958 Playback Con Mask is used to return the - bit-mask for the IEC958 status bits of consumer mode. Similarly, - IEC958 Playback Pro Mask returns the bitmask for - professional mode. They are read-only controls, and are defined - as MIXER controls (iface = - SNDRV_CTL_ELEM_IFACE_MIXER). - - - - Meanwhile, IEC958 Playback Default control is - defined for getting and setting the current default IEC958 - bits. Note that this one is usually defined as a PCM control - (iface = SNDRV_CTL_ELEM_IFACE_PCM), - although in some places it's defined as a MIXER control. - - - - 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 - IEC958 xxx, preferably using - the SNDRV_CTL_NAME_IEC958() macro. - - - - You can find several cases, for example, - pci/emu10k1, - pci/ice1712, or - pci/cmipci.c. - -
- - - - - - - - - Buffer and Memory Management - -
- Buffer Types - - 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 - snd_malloc_xxx_pages() function, where xxx - is the bus type. - - - - The allocation of pages with fallback is - snd_malloc_xxx_pages_fallback(). 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. - - - - The release the pages, call - snd_free_xxx_pages() function. - - - - 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 pre-allocation. - As already written, you can call the following function at - pcm instance construction time (in the case of PCI bus). - - - - - - - - where size is the byte size to be - pre-allocated and the max is the maximum - size to be changed via the prealloc proc file. - The allocator will try to get an area as large as possible - within the given size. - - - - The second argument (type) and the third argument (device pointer) - are dependent on the bus. - In the case of the ISA bus, pass snd_dma_isa_data() - as the third argument with SNDRV_DMA_TYPE_DEV type. - For the continuous buffer unrelated to the bus can be pre-allocated - with SNDRV_DMA_TYPE_CONTINUOUS type and the - snd_dma_continuous_data(GFP_KERNEL) device pointer, - where GFP_KERNEL is the kernel allocation flag to - use. - For the PCI scatter-gather buffers, use - SNDRV_DMA_TYPE_DEV_SG with - snd_dma_pci_data(pci) - (see the - Non-Contiguous Buffers - section). - - - - Once the buffer is pre-allocated, you can use the - allocator in the hw_params callback: - - - - - - - - Note that you have to pre-allocate to use this function. - -
- -
- External Hardware Buffers - - 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). - - - - 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 - copy and - silence 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. - - - - 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. - - - - 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 copy and - silence callbacks as well, - as in the cases above. The examples are found in - rme32.c and rme96.c. - - - - The implementation of the copy and - silence callbacks depends upon - whether the hardware supports interleaved or non-interleaved - samples. The copy callback is - defined like below, a bit - differently depending whether the direction is playback or - capture: - - - - - - - - - - In the case of interleaved samples, the second argument - (channel) is not used. The third argument - (pos) points the - current position offset in frames. - - - - 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. - - - - The last argument is the number of frames to be copied. - - - - 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 - (count) at the specified pointer - (src) to the specified offset - (pos) on the hardware buffer. When - coded like memcpy-like way, the copy would be like: - - - - - - - - - - For the capture direction, you copy the given amount of - data (count) at the specified offset - (pos) on the hardware buffer to the - specified pointer (dst). - - - - - - - - Note that both the position and the amount of data are given - in frames. - - - - In the case of non-interleaved samples, the implementation - will be a bit more complicated. - - - - 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 - isa/gus/gus_pcm.c as an example. - - - - The silence callback is also - implemented in a similar way. - - - - - - - - - - The meanings of arguments are the same as in the - copy - callback, although there is no src/dst - argument. In the case of interleaved samples, the channel - argument has no meaning, as well as on - copy callback. - - - - The role of silence callback is to - set the given amount - (count) of silence data at the - specified offset (pos) 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: - - - - - - - - - - In the case of non-interleaved samples, again, the - implementation becomes a bit more complicated. See, for example, - isa/gus/gus_pcm.c. - -
- -
- Non-Contiguous Buffers - - 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 <sound/pcm.h>. - - - - For creating the SG-buffer handler, call - snd_pcm_lib_preallocate_pages() or - snd_pcm_lib_preallocate_pages_for_all() - with SNDRV_DMA_TYPE_DEV_SG - in the PCM constructor like other PCI pre-allocator. - You need to pass snd_dma_pci_data(pci), - where pci is the struct pci_dev pointer - of the chip as well. - The struct snd_sg_buf instance is created as - substream->dma_private. You can cast - the pointer like: - - - -dma_private; -]]> - - - - - - Then call snd_pcm_lib_malloc_pages() - in the hw_params 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 - snd_pcm_sgbuf_get_addr(). - - - - When a SG-handler is used, you need to set - snd_pcm_sgbuf_ops_page as - the page callback. - (See - page callback section.) - - - - To release the data, call - snd_pcm_lib_free_pages() in the - hw_free callback as usual. - -
- -
- Vmalloc'ed Buffers - - It's possible to use a buffer allocated via - vmalloc, for example, for an intermediate - buffer. Since the allocated pages are not contiguous, you need - to set the page callback to obtain - the physical address at every offset. - - - - The implementation of page callback - would be like this: - - - - - - /* 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); - } -]]> - - - -
- - - - - - - - - Proc Interface - - 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 - <sound/info.h>. - - - - To create a proc file, call - snd_card_proc_new(). - - - - - - - - where the second argument specifies the name of the proc file to be - created. The above example will create a file - my-file under the card directory, - e.g. /proc/asound/card0/my-file. - - - - Like other components, the proc entry created via - snd_card_proc_new() will be registered and - released automatically in the card registration and release - functions. - - - - 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 - snd_info_set_text_ops(). - - - - - - - - where the second argument (chip) is the - private data to be used in the callbacks. The third parameter - specifies the read buffer size and the fourth - (my_proc_read) is the callback function, which - is defined like - - - - - - - - - - - In the read callback, use snd_iprintf() for - output strings, which works just like normal - printf(). For example, - - - -private_data; - - snd_iprintf(buffer, "This is my chip!\n"); - snd_iprintf(buffer, "Port = %ld\n", chip->port); - } -]]> - - - - - - 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: - - - -mode = S_IFREG | S_IRUGO | S_IWUSR; -]]> - - - - and set the write buffer size and the callback - - - -c.text.write = my_proc_write; -]]> - - - - - - For the write callback, you can use - snd_info_get_line() to get a text line, and - snd_info_get_str() to retrieve a string from - the line. Some examples are found in - core/oss/mixer_oss.c, core/oss/and - pcm_oss.c. - - - - For a raw-data proc-file, set the attributes as follows: - - - -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; -]]> - - - - For the raw data, size field must be - set properly. This specifies the maximum size of the proc file access. - - - - 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 - copy_from/to_user() to transfer the - data. - - - - - - - - If the size of the info entry has been set up properly, - count and pos 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. - - - - - - - - - - - Power Management - - 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 - ifdef'ed with - CONFIG_PM. - - - - If the driver fully supports suspend/resume - that is, the device can be - properly resumed to its state when suspend was called, - you can set the SNDRV_PCM_INFO_RESUME 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 - SNDRV_PCM_TRIGGER_RESUME after the resume - callback completes. - - - - 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 - snd_pcm_prepare() and restart the stream - appropriately. Hence, you can define suspend/resume callbacks - below but don't set SNDRV_PCM_INFO_RESUME - info flag to the PCM. - - - - Note that the trigger with SUSPEND can always be called when - snd_pcm_suspend_all is called, - regardless of the SNDRV_PCM_INFO_RESUME flag. - The RESUME flag affects only the behavior - of snd_pcm_resume(). - (Thus, in theory, - SNDRV_PCM_TRIGGER_RESUME isn't needed - to be handled in the trigger callback when no - SNDRV_PCM_INFO_RESUME flag is set. But, - it's better to keep it for compatibility reasons.) - - - 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: - - - - - - - - - - The scheme of the real suspend job is as follows. - - - Retrieve the card and the chip data. - Call snd_power_change_state() with - SNDRV_CTL_POWER_D3hot to change the - power status. - Call snd_pcm_suspend_all() to suspend the running PCM streams. - If AC97 codecs are used, call - snd_ac97_suspend() for each codec. - Save the register values if necessary. - Stop the hardware if necessary. - Disable the PCI device by calling - pci_disable_device(). Then, call - pci_save_state() at last. - - - - - A typical code would be like: - - - -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; - } -]]> - - - - - - The scheme of the real resume job is as follows. - - - Retrieve the card and the chip data. - Set up PCI. First, call pci_restore_state(). - Then enable the pci device again by calling pci_enable_device(). - Call pci_set_master() if necessary, too. - Re-initialize the chip. - Restore the saved registers if necessary. - Resume the mixer, e.g. calling - snd_ac97_resume(). - Restart the hardware (if any). - Call snd_power_change_state() with - SNDRV_CTL_POWER_D0 to notify the processes. - - - - - A typical code would be like: - - - -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; - } -]]> - - - - - - As shown in the above, it's better to save registers after - suspending the PCM operations via - snd_pcm_suspend_all() or - snd_pcm_suspend(). 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 SNDRV_PCM_TRIGGER_RESUME - when necessary. - - - - 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 - private_data field, in case you - created the chip data individually. - - - -dev, index[dev], id[dev], THIS_MODULE, - 0, &card); - .... - chip = kzalloc(sizeof(*chip), GFP_KERNEL); - .... - card->private_data = chip; - .... - } -]]> - - - - When you created the chip data with - snd_card_new(), it's anyway accessible - via private_data field. - - - -dev, index[dev], id[dev], THIS_MODULE, - sizeof(struct mychip), &card); - .... - chip = card->private_data; - .... - } -]]> - - - - - - - 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. - - - - And next, set suspend/resume callbacks to the pci_driver. - - - - - - - - - - - - - - - - Module Parameters - - There are standard module options for ALSA. At least, each - module should have the index, - id and enable - options. - - - - If the module supports multiple cards (usually up to - 8 = SNDRV_CARDS cards), they should be - arrays. The default initial values are defined already as - constants for easier programming: - - - - - - - - - - If the module supports only a single card, they could be single - variables, instead. enable option is not - always necessary in this case, but it would be better to have a - dummy option for compatibility. - - - - The module parameters must be declared with the standard - module_param()(), - module_param_array()() and - MODULE_PARM_DESC() macros. - - - - The typical coding would be like below: - - - - - - - - - - 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 tainted. - - - - - - - - - - - - - - - - How To Put Your Driver Into ALSA Tree -
- General - - 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. - - - - Suppose that you create a new PCI driver for the card - xyz. The card module name would be - snd-xyz. The new driver is usually put into the alsa-driver - tree, alsa-driver/pci 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 alsa-kernel/pci) and eventually - will be integrated into the Linux 2.6 tree (the directory would be - linux/sound/pci). - - - - 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. - -
- -
- Driver with A Single Source File - - - - - Modify alsa-driver/pci/Makefile - - - - Suppose you have a file xyz.c. Add the following - two lines - - - - - - - - - - - Create the Kconfig entry - - - - Add the new entry of Kconfig for your xyz driver. - - - - - - - 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. - - - - 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. - - - - For the details of Kconfig script, refer to the kbuild - documentation. - - - - - - - Run cvscompile script to re-generate the configure script and - build the whole stuff again. - - - - -
- -
- Drivers with Several Source Files - - Suppose that the driver snd-xyz have several source files. - They are located in the new subdirectory, - pci/xyz. - - - - - Add a new directory (xyz) in - alsa-driver/pci/Makefile as below - - - - - - - - - - - - Under the directory xyz, create a Makefile - - - Sample Makefile for a driver xyz - - - - - - - - - - Create the Kconfig entry - - - - This procedure is as same as in the last section. - - - - - - Run cvscompile script to re-generate the configure script and - build the whole stuff again. - - - - -
- - - - - - - - Useful Functions - -
- <function>snd_printk()</function> and friends - - ALSA provides a verbose version of the - printk() function. If a kernel config - CONFIG_SND_VERBOSE_PRINTK is set, this - function prints the given message together with the file name - and the line of the caller. The KERN_XXX - prefix is processed as - well as the original printk() does, so it's - recommended to add this prefix, e.g. - - - - - - - - - - There are also printk()'s for - debugging. snd_printd() can be used for - general debugging purposes. If - CONFIG_SND_DEBUG is set, this function is - compiled, and works just like - snd_printk(). If the ALSA is compiled - without the debugging flag, it's ignored. - - - - snd_printdd() is compiled in only when - CONFIG_SND_DEBUG_VERBOSE is set. Please note - that CONFIG_SND_DEBUG_VERBOSE is not set as default - even if you configure the alsa-driver with - option. You need to give - explicitly option instead. - -
- -
- <function>snd_BUG()</function> - - It shows the BUG? message and - stack trace as well as snd_BUG_ON at the point. - It's useful to show that a fatal error happens there. - - - When no debug flag is set, this macro is ignored. - -
- -
- <function>snd_BUG_ON()</function> - - snd_BUG_ON() macro is similar with - WARN_ON() macro. For example, - - - - - - - - or it can be used as the condition, - - - - - - - - - - The macro takes an conditional expression to evaluate. - When CONFIG_SND_DEBUG, is set, if the - expression is non-zero, it shows the warning message such as - BUG? (xxx) - normally followed by stack trace. - - In both cases it returns the evaluated value. - - -
- - - - - - - - - Acknowledgments - - I would like to thank Phil Kerr for his help for improvement and - corrections of this document. - - - Kevin Conder reformatted the original plain-text to the - DocBook format. - - - Giuliano Pochini corrected typos and contributed the example codes - in the hardware constraints section. - - - -- cgit v1.2.3-59-g8ed1b