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Diffstat (limited to 'Documentation/w1/w1.generic')
| -rw-r--r-- | Documentation/w1/w1.generic | 121 |
1 files changed, 0 insertions, 121 deletions
diff --git a/Documentation/w1/w1.generic b/Documentation/w1/w1.generic deleted file mode 100644 index c51b1ab012d0..000000000000 --- a/Documentation/w1/w1.generic +++ /dev/null @@ -1,121 +0,0 @@ -The 1-wire (w1) subsystem ------------------------------------------------------------------- -The 1-wire bus is a simple master-slave bus that communicates via a single -signal wire (plus ground, so two wires). - -Devices communicate on the bus by pulling the signal to ground via an open -drain output and by sampling the logic level of the signal line. - -The w1 subsystem provides the framework for managing w1 masters and -communication with slaves. - -All w1 slave devices must be connected to a w1 bus master device. - -Example w1 master devices: - DS9490 usb device - W1-over-GPIO - DS2482 (i2c to w1 bridge) - Emulated devices, such as a RS232 converter, parallel port adapter, etc - - -What does the w1 subsystem do? ------------------------------------------------------------------- -When a w1 master driver registers with the w1 subsystem, the following occurs: - - - sysfs entries for that w1 master are created - - the w1 bus is periodically searched for new slave devices - -When a device is found on the bus, w1 core tries to load the driver for its family -and check if it is loaded. If so, the family driver is attached to the slave. -If there is no driver for the family, default one is assigned, which allows to perform -almost any kind of operations. Each logical operation is a transaction -in nature, which can contain several (two or one) low-level operations. -Let's see how one can read EEPROM context: -1. one must write control buffer, i.e. buffer containing command byte -and two byte address. At this step bus is reset and appropriate device -is selected using either W1_SKIP_ROM or W1_MATCH_ROM command. -Then provided control buffer is being written to the wire. -2. reading. This will issue reading eeprom response. - -It is possible that between 1. and 2. w1 master thread will reset bus for searching -and slave device will be even removed, but in this case 0xff will -be read, since no device was selected. - - -W1 device families ------------------------------------------------------------------- -Slave devices are handled by a driver written for a family of w1 devices. - -A family driver populates a struct w1_family_ops (see w1_family.h) and -registers with the w1 subsystem. - -Current family drivers: -w1_therm - (ds18?20 thermal sensor family driver) - provides temperature reading function which is bound to ->rbin() method - of the above w1_family_ops structure. - -w1_smem - driver for simple 64bit memory cell provides ID reading method. - -You can call above methods by reading appropriate sysfs files. - - -What does a w1 master driver need to implement? ------------------------------------------------------------------- - -The driver for w1 bus master must provide at minimum two functions. - -Emulated devices must provide the ability to set the output signal level -(write_bit) and sample the signal level (read_bit). - -Devices that support the 1-wire natively must provide the ability to write and -sample a bit (touch_bit) and reset the bus (reset_bus). - -Most hardware provides higher-level functions that offload w1 handling. -See struct w1_bus_master definition in w1.h for details. - - -w1 master sysfs interface ------------------------------------------------------------------- -<xx-xxxxxxxxxxxx> - A directory for a found device. The format is family-serial -bus - (standard) symlink to the w1 bus -driver - (standard) symlink to the w1 driver -w1_master_add - (rw) manually register a slave device -w1_master_attempts - (ro) the number of times a search was attempted -w1_master_max_slave_count - - (rw) maximum number of slaves to search for at a time -w1_master_name - (ro) the name of the device (w1_bus_masterX) -w1_master_pullup - (rw) 5V strong pullup 0 enabled, 1 disabled -w1_master_remove - (rw) manually remove a slave device -w1_master_search - (rw) the number of searches left to do, - -1=continual (default) -w1_master_slave_count - - (ro) the number of slaves found -w1_master_slaves - (ro) the names of the slaves, one per line -w1_master_timeout - (ro) the delay in seconds between searches -w1_master_timeout_us - - (ro) the delay in microseconds beetwen searches - -If you have a w1 bus that never changes (you don't add or remove devices), -you can set the module parameter search_count to a small positive number -for an initially small number of bus searches. Alternatively it could be -set to zero, then manually add the slave device serial numbers by -w1_master_add device file. The w1_master_add and w1_master_remove files -generally only make sense when searching is disabled, as a search will -redetect manually removed devices that are present and timeout manually -added devices that aren't on the bus. - -Bus searches occur at an interval, specified as a summ of timeout and -timeout_us module parameters (either of which may be 0) for as long as -w1_master_search remains greater than 0 or is -1. Each search attempt -decrements w1_master_search by 1 (down to 0) and increments -w1_master_attempts by 1. - -w1 slave sysfs interface ------------------------------------------------------------------- -bus - (standard) symlink to the w1 bus -driver - (standard) symlink to the w1 driver -name - the device name, usually the same as the directory name -w1_slave - (optional) a binary file whose meaning depends on the - family driver -rw - (optional) created for slave devices which do not have - appropriate family driver. Allows to read/write binary data. |