73 lines
2.4 KiB
ReStructuredText
73 lines
2.4 KiB
ReStructuredText
========================
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Kernel driver w1_ds28e17
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========================
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Supported chips:
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* Maxim DS28E17 1-Wire-to-I2C Master Bridge
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supported family codes:
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================= ====
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W1_FAMILY_DS28E17 0x19
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================= ====
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Author: Jan Kandziora <jjj@gmx.de>
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Description
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-----------
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The DS28E17 is a Onewire slave device which acts as an I2C bus master.
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This driver creates a new I2C bus for any DS28E17 device detected. I2C buses
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come and go as the DS28E17 devices come and go. I2C slave devices connected to
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a DS28E17 can be accessed by the kernel or userspace tools as if they were
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connected to a "native" I2C bus master.
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An udev rule like the following::
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SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", ATTRS{name}=="w1-19-*", \
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SYMLINK+="i2c-$attr{name}"
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may be used to create stable /dev/i2c- entries based on the unique id of the
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DS28E17 chip.
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Driver parameters are:
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speed:
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This sets up the default I2C speed a DS28E17 get configured for as soon
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it is connected. The power-on default of the DS28E17 is 400kBaud, but
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chips may come and go on the Onewire bus without being de-powered and
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as soon the "w1_ds28e17" driver notices a freshly connected, or
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reconnected DS28E17 device on the Onewire bus, it will re-apply this
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setting.
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Valid values are 100, 400, 900 [kBaud]. Any other value means to leave
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alone the current DS28E17 setting on detect. The default value is 100.
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stretch:
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This sets up the default stretch value used for freshly connected
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DS28E17 devices. It is a multiplier used on the calculation of the busy
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wait time for an I2C transfer. This is to account for I2C slave devices
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which make heavy use of the I2C clock stretching feature and thus, the
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needed timeout cannot be pre-calculated correctly. As the w1_ds28e17
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driver checks the DS28E17's busy flag in a loop after the precalculated
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wait time, it should be hardly needed to tweak this setting.
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Leave it at 1 unless you get ETIMEDOUT errors and a "w1_slave_driver
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19-00000002dbd8: busy timeout" in the kernel log.
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Valid values are 1 to 9. The default is 1.
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The driver creates sysfs files /sys/bus/w1/devices/19-<id>/speed and
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/sys/bus/w1/devices/19-<id>/stretch for each device, preloaded with the default
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settings from the driver parameters. They may be changed anytime. In addition a
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directory /sys/bus/w1/devices/19-<id>/i2c-<nnn> for the I2C bus master sysfs
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structure is created.
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See https://github.com/ianka/w1_ds28e17 for even more information.
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