1 =========================================
2 Introduction to the 1-wire (w1) subsystem
3 =========================================
4
5 The 1-wire bus is a simple master-slave bus th
6 signal wire (plus ground, so two wires).
7
8 Devices communicate on the bus by pulling the
9 drain output and by sampling the logic level o
10
11 The w1 subsystem provides the framework for ma
12 communication with slaves.
13
14 All w1 slave devices must be connected to a w1
15
16 Example w1 master devices:
17
18 - DS9490 usb device
19 - W1-over-GPIO
20 - DS2482 (i2c to w1 bridge)
21 - Emulated devices, such as a RS232 conver
22
23
24 What does the w1 subsystem do?
25 ------------------------------
26
27 When a w1 master driver registers with the w1
28
29 - sysfs entries for that w1 master are create
30 - the w1 bus is periodically searched for new
31
32 When a device is found on the bus, w1 core tri
33 and check if it is loaded. If so, the family d
34 If there is no driver for the family, default
35 almost any kind of operations. Each logical op
36 in nature, which can contain several (two or o
37 Let's see how one can read EEPROM context:
38 1. one must write control buffer, i.e. buffer
39 and two byte address. At this step bus is rese
40 is selected using either W1_SKIP_ROM or W1_MAT
41 Then provided control buffer is being written
42 2. reading. This will issue reading eeprom res
43
44 It is possible that between 1. and 2. w1 maste
45 and slave device will be even removed, but in
46 be read, since no device was selected.
47
48
49 W1 device families
50 ------------------
51
52 Slave devices are handled by a driver written
53
54 A family driver populates a struct w1_family_o
55 registers with the w1 subsystem.
56
57 Current family drivers:
58
59 w1_therm
60 - (ds18?20 thermal sensor family driver)
61 provides temperature reading function whic
62 of the above w1_family_ops structure.
63
64 w1_smem
65 - driver for simple 64bit memory cell provid
66
67 You can call above methods by reading appropri
68
69
70 What does a w1 master driver need to implement
71 ----------------------------------------------
72
73 The driver for w1 bus master must provide at m
74
75 Emulated devices must provide the ability to s
76 (write_bit) and sample the signal level (read_
77
78 Devices that support the 1-wire natively must
79 sample a bit (touch_bit) and reset the bus (re
80
81 Most hardware provides higher-level functions
82 See struct w1_bus_master definition in w1.h fo
83
84
85 w1 master sysfs interface
86 -------------------------
87
88 ========================= ====================
89 <xx-xxxxxxxxxxxx> A directory for a fo
90 family-serial
91 bus (standard) symlink t
92 driver (standard) symlink t
93 w1_master_add (rw) manually regist
94 w1_master_attempts (ro) the number of t
95 w1_master_max_slave_count (rw) maximum number
96 w1_master_name (ro) the name of the
97 w1_master_pullup (rw) 5V strong pullu
98 w1_master_remove (rw) manually remove
99 w1_master_search (rw) the number of s
100 -1=continual (defaul
101 w1_master_slave_count (ro) the number of s
102 w1_master_slaves (ro) the names of th
103 w1_master_timeout (ro) the delay in se
104 w1_master_timeout_us (ro) the delay in mi
105 ========================= ====================
106
107 If you have a w1 bus that never changes (you d
108 you can set the module parameter search_count
109 for an initially small number of bus searches.
110 set to zero, then manually add the slave devic
111 w1_master_add device file. The w1_master_add
112 generally only make sense when searching is di
113 redetect manually removed devices that are pre
114 added devices that aren't on the bus.
115
116 Bus searches occur at an interval, specified a
117 timeout_us module parameters (either of which
118 w1_master_search remains greater than 0 or is
119 decrements w1_master_search by 1 (down to 0) a
120 w1_master_attempts by 1.
121
122 w1 slave sysfs interface
123 ------------------------
124
125 =================== ==========================
126 bus (standard) symlink to the
127 driver (standard) symlink to the
128 name the device name, usually t
129 w1_slave (optional) a binary file w
130 family driver
131 rw (optional) created for sla
132 appropriate family driver.
133 =================== ==========================
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