Evgeniy Polyakov | 4754639 | 2005-06-04 01:31:47 +0400 | [diff] [blame^] | 1 | The 1-wire (w1) subsystem |
| 2 | ------------------------------------------------------------------ |
| 3 | The 1-wire bus is a simple master-slave bus that communicates via a single |
| 4 | signal wire (plus ground, so two wires). |
| 5 | |
| 6 | Devices communicate on the bus by pulling the signal to ground via an open |
| 7 | drain output and by sampling the logic level of the signal line. |
| 8 | |
| 9 | The w1 subsystem provides the framework for managing w1 masters and |
| 10 | communication with slaves. |
| 11 | |
| 12 | All w1 slave devices must be connected to a w1 bus master device. |
| 13 | |
| 14 | Example w1 master devices: |
| 15 | DS9490 usb device |
| 16 | W1-over-GPIO |
| 17 | DS2482 (i2c to w1 bridge) |
| 18 | Emulated devices, such as a RS232 converter, parallel port adapter, etc |
| 19 | |
| 20 | |
| 21 | What does the w1 subsystem do? |
| 22 | ------------------------------------------------------------------ |
| 23 | When a w1 master driver registers with the w1 subsystem, the following occurs: |
| 24 | |
| 25 | - sysfs entries for that w1 master are created |
| 26 | - the w1 bus is periodically searched for new slave devices |
| 27 | |
| 28 | When a device is found on the bus, w1 core checks if driver for it's family is |
| 29 | loaded. If so, the family driver is attached to the slave. |
| 30 | If there is no driver for the family, a simple sysfs entry is created |
| 31 | for the slave device. |
| 32 | |
| 33 | |
| 34 | W1 device families |
| 35 | ------------------------------------------------------------------ |
| 36 | Slave devices are handled by a driver written for a family of w1 devices. |
| 37 | |
| 38 | A family driver populates a struct w1_family_ops (see w1_family.h) and |
| 39 | registers with the w1 subsystem. |
| 40 | |
| 41 | Current family drivers: |
| 42 | w1_therm - (ds18?20 thermal sensor family driver) |
| 43 | provides temperature reading function which is bound to ->rbin() method |
| 44 | of the above w1_family_ops structure. |
| 45 | |
| 46 | w1_smem - driver for simple 64bit memory cell provides ID reading method. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 47 | |
| 48 | You can call above methods by reading appropriate sysfs files. |
Evgeniy Polyakov | 4754639 | 2005-06-04 01:31:47 +0400 | [diff] [blame^] | 49 | |
| 50 | |
| 51 | What does a w1 master driver need to implement? |
| 52 | ------------------------------------------------------------------ |
| 53 | |
| 54 | The driver for w1 bus master must provide at minimum two functions. |
| 55 | |
| 56 | Emulated devices must provide the ability to set the output signal level |
| 57 | (write_bit) and sample the signal level (read_bit). |
| 58 | |
| 59 | Devices that support the 1-wire natively must provide the ability to write and |
| 60 | sample a bit (touch_bit) and reset the bus (reset_bus). |
| 61 | |
| 62 | Most hardware provides higher-level functions that offload w1 handling. |
| 63 | See struct w1_bus_master definition in w1.h for details. |
| 64 | |
| 65 | |
| 66 | w1 master sysfs interface |
| 67 | ------------------------------------------------------------------ |
| 68 | <xx-xxxxxxxxxxxxx> - a directory for a found device. The format is family-serial |
| 69 | bus - (standard) symlink to the w1 bus |
| 70 | driver - (standard) symlink to the w1 driver |
| 71 | w1_master_attempts - the number of times a search was attempted |
| 72 | w1_master_max_slave_count |
| 73 | - the maximum slaves that may be attached to a master |
| 74 | w1_master_name - the name of the device (w1_bus_masterX) |
| 75 | w1_master_search - the number of searches left to do, -1=continual (default) |
| 76 | w1_master_slave_count |
| 77 | - the number of slaves found |
| 78 | w1_master_slaves - the names of the slaves, one per line |
| 79 | w1_master_timeout - the delay in seconds between searches |
| 80 | |
| 81 | If you have a w1 bus that never changes (you don't add or remove devices), |
| 82 | you can set w1_master_search to a positive value to disable searches. |
| 83 | |
| 84 | |
| 85 | w1 slave sysfs interface |
| 86 | ------------------------------------------------------------------ |
| 87 | bus - (standard) symlink to the w1 bus |
| 88 | driver - (standard) symlink to the w1 driver |
| 89 | name - the device name, usually the same as the directory name |
| 90 | w1_slave - (optional) a binary file whose meaning depends on the |
| 91 | family driver |
| 92 | |