1 ========================
2 Kernel driver w1_ds28e17
3 ========================
4
5 Supported chips:
6
7 * Maxim DS28E17 1-Wire-to-I2C Master Bridge
8
9 supported family codes:
10
11 ================= ====
12 W1_FAMILY_DS28E17 0x19
13 ================= ====
14
15 Author: Jan Kandziora <jjj@gmx.de>
16
17
18 Description
19 -----------
20 The DS28E17 is a Onewire slave device which acts as an I2C bus master.
21
22 This driver creates a new I2C bus for any DS28E17 device detected. I2C buses
23 come and go as the DS28E17 devices come and go. I2C slave devices connected to
24 a DS28E17 can be accessed by the kernel or userspace tools as if they were
25 connected to a "native" I2C bus master.
26
27
28 An udev rule like the following::
29
30 SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", ATTRS{name}=="w1-19-*", \
31 SYMLINK+="i2c-$attr{name}"
32
33 may be used to create stable /dev/i2c- entries based on the unique id of the
34 DS28E17 chip.
35
36
37 Driver parameters are:
38
39 speed:
40 This sets up the default I2C speed a DS28E17 get configured for as soon
41 it is connected. The power-on default of the DS28E17 is 400kBaud, but
42 chips may come and go on the Onewire bus without being de-powered and
43 as soon the "w1_ds28e17" driver notices a freshly connected, or
44 reconnected DS28E17 device on the Onewire bus, it will re-apply this
45 setting.
46
47 Valid values are 100, 400, 900 [kBaud]. Any other value means to leave
48 alone the current DS28E17 setting on detect. The default value is 100.
49
50 stretch:
51 This sets up the default stretch value used for freshly connected
52 DS28E17 devices. It is a multiplier used on the calculation of the busy
53 wait time for an I2C transfer. This is to account for I2C slave devices
54 which make heavy use of the I2C clock stretching feature and thus, the
55 needed timeout cannot be pre-calculated correctly. As the w1_ds28e17
56 driver checks the DS28E17's busy flag in a loop after the precalculated
57 wait time, it should be hardly needed to tweak this setting.
58
59 Leave it at 1 unless you get ETIMEDOUT errors and a "w1_slave_driver
60 19-00000002dbd8: busy timeout" in the kernel log.
61
62 Valid values are 1 to 9. The default is 1.
63
64
65 The driver creates sysfs files /sys/bus/w1/devices/19-<id>/speed and
66 /sys/bus/w1/devices/19-<id>/stretch for each device, preloaded with the default
67 settings from the driver parameters. They may be changed anytime. In addition a
68 directory /sys/bus/w1/devices/19-<id>/i2c-<nnn> for the I2C bus master sysfs
69 structure is created.
70
71
72 See https://github.com/ianka/w1_ds28e17 for even more information.
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