| The 1-wire (w1) subsystem |
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| The 1-wire bus is a simple master-slave bus that communicates via a single |
| signal wire (plus ground, so two wires). |
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| 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. |
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| The w1 subsystem provides the framework for managing w1 masters and |
| communication with slaves. |
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| All w1 slave devices must be connected to a w1 bus master device. |
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| 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 |
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| What does the w1 subsystem do? |
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| When a w1 master driver registers with the w1 subsystem, the following occurs: |
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| - sysfs entries for that w1 master are created |
| - the w1 bus is periodically searched for new slave devices |
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| 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. |
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| W1 device families |
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| Slave devices are handled by a driver written for a family of w1 devices. |
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| A family driver populates a struct w1_family_ops (see w1_family.h) and |
| registers with the w1 subsystem. |
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| 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. |
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| w1_smem - driver for simple 64bit memory cell provides ID reading method. |
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| You can call above methods by reading appropriate sysfs files. |
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| What does a w1 master driver need to implement? |
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| The driver for w1 bus master must provide at minimum two functions. |
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| Emulated devices must provide the ability to set the output signal level |
| (write_bit) and sample the signal level (read_bit). |
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| 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). |
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| Most hardware provides higher-level functions that offload w1 handling. |
| See struct w1_bus_master definition in w1.h for details. |
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| w1 master sysfs interface |
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| <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 |
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| 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. |
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| w1 slave sysfs interface |
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| 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 |
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