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