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Diffstat (limited to 'Documentation/w1')
| -rw-r--r-- | Documentation/w1/w1.generic | 107 |
1 files changed, 90 insertions, 17 deletions
diff --git a/Documentation/w1/w1.generic b/Documentation/w1/w1.generic index eace3046a858..f937fbe1cacb 100644 --- a/Documentation/w1/w1.generic +++ b/Documentation/w1/w1.generic @@ -1,19 +1,92 @@ -Any w1 device must be connected to w1 bus master device - for example -ds9490 usb device or w1-over-GPIO or RS232 converter. -Driver for w1 bus master must provide several functions(you can find -them in struct w1_bus_master definition in w1.h) which then will be -called by w1 core to send various commands over w1 bus(by default it is -reset and search commands). When some device is found on the bus, w1 core -checks if driver for it's family is loaded. -If driver is loaded w1 core creates new w1_slave object and registers it -in the system(creates some generic sysfs files(struct w1_family_ops in -w1_family.h), notifies any registered listener and so on...). -It is device driver's business to provide any communication method -upstream. -For example w1_therm driver(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. +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 checks if driver for it's family is +loaded. If so, the family driver is attached to the slave. +If there is no driver for the family, a simple sysfs entry is created +for the slave device. + + +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-xxxxxxxxxxxxx> - 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_attempts - the number of times a search was attempted +w1_master_max_slave_count + - the maximum slaves that may be attached to a master +w1_master_name - the name of the device (w1_bus_masterX) +w1_master_search - the number of searches left to do, -1=continual (default) +w1_master_slave_count + - the number of slaves found +w1_master_slaves - the names of the slaves, one per line +w1_master_timeout - the delay in seconds between searches + +If you have a w1 bus that never changes (you don't add or remove devices), +you can set w1_master_search to a positive value to disable searches. + + +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 + |