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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.

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).
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.
9	The w1 subsystem provides the framework for managing w1 masters and
10	communication with slaves.
12	All w1 slave devices must be connected to a w1 bus master device.
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
21	What does the w1 subsystem do?
22	------------------------------------------------------------------
23	When a w1 master driver registers with the w1 subsystem, the following occurs:
25	 - sysfs entries for that w1 master are created
26	 - the w1 bus is periodically searched for new slave devices
28	When a device is found on the bus, w1 core tries to load the driver for its family
29	and check if it is loaded. If so, the family driver is attached to the slave.
30	If there is no driver for the family, default one is assigned, which allows to perform
31	almost any kind of operations. Each logical operation is a transaction
32	in nature, which can contain several (two or one) low-level operations.
33	Let's see how one can read EEPROM context:
34	1. one must write control buffer, i.e. buffer containing command byte
35	and two byte address. At this step bus is reset and appropriate device
36	is selected using either W1_SKIP_ROM or W1_MATCH_ROM command.
37	Then provided control buffer is being written to the wire.
38	2. reading. This will issue reading eeprom response.
40	It is possible that between 1. and 2. w1 master thread will reset bus for searching
41	and slave device will be even removed, but in this case 0xff will
42	be read, since no device was selected.
45	W1 device families
46	------------------------------------------------------------------
47	Slave devices are handled by a driver written for a family of w1 devices.
49	A family driver populates a struct w1_family_ops (see w1_family.h) and
50	registers with the w1 subsystem.
52	Current family drivers:
53	w1_therm - (ds18?20 thermal sensor family driver)
54	    provides temperature reading function which is bound to ->rbin() method
55	    of the above w1_family_ops structure.
57	w1_smem - driver for simple 64bit memory cell provides ID reading method.
59	You can call above methods by reading appropriate sysfs files.
62	What does a w1 master driver need to implement?
63	------------------------------------------------------------------
65	The driver for w1 bus master must provide at minimum two functions.
67	Emulated devices must provide the ability to set the output signal level
68	(write_bit) and sample the signal level (read_bit).
70	Devices that support the 1-wire natively must provide the ability to write and
71	sample a bit (touch_bit) and reset the bus (reset_bus).
73	Most hardware provides higher-level functions that offload w1 handling.
74	See struct w1_bus_master definition in w1.h for details.
77	w1 master sysfs interface
78	------------------------------------------------------------------
79	<xx-xxxxxxxxxxxxx> - A directory for a found device. The format is family-serial
80	bus                - (standard) symlink to the w1 bus
81	driver             - (standard) symlink to the w1 driver
82	w1_master_add      - (rw) manually register a slave device
83	w1_master_attempts - (ro) the number of times a search was attempted
84	w1_master_max_slave_count
85	                   - (rw) maximum number of slaves to search for at a time
86	w1_master_name     - (ro) the name of the device (w1_bus_masterX)
87	w1_master_pullup   - (rw) 5V strong pullup 0 enabled, 1 disabled
88	w1_master_remove   - (rw) manually remove a slave device
89	w1_master_search   - (rw) the number of searches left to do,
90			     -1=continual (default)
91	w1_master_slave_count
92	                   - (ro) the number of slaves found
93	w1_master_slaves   - (ro) the names of the slaves, one per line
94	w1_master_timeout  - (ro) the delay in seconds between searches
95	w1_master_timeout_us
96	                   - (ro) the delay in microseconds beetwen searches
98	If you have a w1 bus that never changes (you don't add or remove devices),
99	you can set the module parameter search_count to a small positive number
100	for an initially small number of bus searches.  Alternatively it could be
101	set to zero, then manually add the slave device serial numbers by
102	w1_master_add device file.  The w1_master_add and w1_master_remove files
103	generally only make sense when searching is disabled, as a search will
104	redetect manually removed devices that are present and timeout manually
105	added devices that aren't on the bus.
107	Bus searches occur at an interval, specified as a summ of timeout and
108	timeout_us module parameters (either of which may be 0) for as long as
109	w1_master_search remains greater than 0 or is -1.  Each search attempt
110	decrements w1_master_search by 1 (down to 0) and increments
111	w1_master_attempts by 1.
113	w1 slave sysfs interface
114	------------------------------------------------------------------
115	bus                - (standard) symlink to the w1 bus
116	driver             - (standard) symlink to the w1 driver
117	name               - the device name, usually the same as the directory name
118	w1_slave           - (optional) a binary file whose meaning depends on the
119	                     family driver
120	rw		   - (optional) created for slave devices which do not have
121			     appropriate family driver. Allows to read/write binary data.
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