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-rw-r--r--Documentation/w1/w1.generic107
1 files changed, 90 insertions, 17 deletions
diff --git a/Documentation/w1/w1.generic b/Documentation/w1/w1.generic
index eace3046a858..f937fbe1cacb 100644
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1Any w1 device must be connected to w1 bus master device - for example 1The 1-wire (w1) subsystem
2ds9490 usb device or w1-over-GPIO or RS232 converter. 2------------------------------------------------------------------
3Driver for w1 bus master must provide several functions(you can find 3The 1-wire bus is a simple master-slave bus that communicates via a single
4them in struct w1_bus_master definition in w1.h) which then will be 4signal wire (plus ground, so two wires).
5called by w1 core to send various commands over w1 bus(by default it is 5
6reset and search commands). When some device is found on the bus, w1 core 6Devices communicate on the bus by pulling the signal to ground via an open
7checks if driver for it's family is loaded. 7drain output and by sampling the logic level of the signal line.
8If driver is loaded w1 core creates new w1_slave object and registers it 8
9in the system(creates some generic sysfs files(struct w1_family_ops in 9The w1 subsystem provides the framework for managing w1 masters and
10w1_family.h), notifies any registered listener and so on...). 10communication with slaves.
11It is device driver's business to provide any communication method 11
12upstream. 12All w1 slave devices must be connected to a w1 bus master device.
13For example w1_therm driver(ds18?20 thermal sensor family driver) 13
14provides temperature reading function which is bound to ->rbin() method 14Example w1 master devices:
15of the above w1_family_ops structure. 15 DS9490 usb device
16w1_smem - driver for simple 64bit memory cell provides ID reading 16 W1-over-GPIO
17method. 17 DS2482 (i2c to w1 bridge)
18 Emulated devices, such as a RS232 converter, parallel port adapter, etc
19
20
21What does the w1 subsystem do?
22------------------------------------------------------------------
23When 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
28When a device is found on the bus, w1 core checks if driver for it's family is
29loaded. If so, the family driver is attached to the slave.
30If there is no driver for the family, a simple sysfs entry is created
31for the slave device.
32
33
34W1 device families
35------------------------------------------------------------------
36Slave devices are handled by a driver written for a family of w1 devices.
37
38A family driver populates a struct w1_family_ops (see w1_family.h) and
39registers with the w1 subsystem.
40
41Current family drivers:
42w1_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
46w1_smem - driver for simple 64bit memory cell provides ID reading method.
18 47
19You can call above methods by reading appropriate sysfs files. 48You can call above methods by reading appropriate sysfs files.
49
50
51What does a w1 master driver need to implement?
52------------------------------------------------------------------
53
54The driver for w1 bus master must provide at minimum two functions.
55
56Emulated devices must provide the ability to set the output signal level
57(write_bit) and sample the signal level (read_bit).
58
59Devices that support the 1-wire natively must provide the ability to write and
60sample a bit (touch_bit) and reset the bus (reset_bus).
61
62Most hardware provides higher-level functions that offload w1 handling.
63See struct w1_bus_master definition in w1.h for details.
64
65
66w1 master sysfs interface
67------------------------------------------------------------------
68<xx-xxxxxxxxxxxxx> - a directory for a found device. The format is family-serial
69bus - (standard) symlink to the w1 bus
70driver - (standard) symlink to the w1 driver
71w1_master_attempts - the number of times a search was attempted
72w1_master_max_slave_count
73 - the maximum slaves that may be attached to a master
74w1_master_name - the name of the device (w1_bus_masterX)
75w1_master_search - the number of searches left to do, -1=continual (default)
76w1_master_slave_count
77 - the number of slaves found
78w1_master_slaves - the names of the slaves, one per line
79w1_master_timeout - the delay in seconds between searches
80
81If you have a w1 bus that never changes (you don't add or remove devices),
82you can set w1_master_search to a positive value to disable searches.
83
84
85w1 slave sysfs interface
86------------------------------------------------------------------
87bus - (standard) symlink to the w1 bus
88driver - (standard) symlink to the w1 driver
89name - the device name, usually the same as the directory name
90w1_slave - (optional) a binary file whose meaning depends on the
91 family driver
92