SI70XXTEMP(4) FreeBSD Kernel Interfaces Manual SI70XXTEMP(4)
NAME
si70xxtemp - Driver for Silicon Labs SI7013/SI7020/SI7021, HTU21D and
SHT21 sensor chip via I2C bus
SYNOPSIS
si70xxtemp* at iic? addr 0x40
DESCRIPTION
The si70xxtemp driver provides measurements from the SI7013/SI7020/SI7021
humidity/temperature sensors via the envsys(4) framework. The si70xxtemp
addr argument selects the address at the iic(4) bus. The resolution,
heater control and crc validity can be changed through sysctl(8) nodes.
SYSCTL VARIABLES
The following sysctl(3) variables are provided:
hw.si70xxtemp0.resolutions
Lists the resolutions supported by the driver and chip.
hw.si70xxtemp0.resolution
Set the resolution, or number of bits, used for %RH and
temperature. Use one of the strings listed in
hw.si70xxtemp.resolutions.
hw.si70xxtemp0.ignorecrc
If set, the crc calculation for %RH and temperature will be
ignored.
hw.si70xxtemp0.vddok
If 1, the chip is getting enough power.
hw.si70xxtemp0.heateron
Turn the heater on and off.
hw.si70xxtemp0.heaterstrength
From 1 to 6, the amount of energy put into the heater. The
higher the number, the more power used.
Some HTU21D chips do not support a heater register. These chips
are detected and the heater features of the driver will be
disabled.
hw.si70xxtemp0.debug
If the driver is compiled with SI70XX_DEBUG, this node will
appear and can be used to set the debugging level.
hw.si70xxtemp0.readattempts
To read %RH or temperature the driver uses a No Hold Master
command. This command needs to be sent to the device, a wait
must then occur and then another read command is sent to read
back the values. Depending on the resolution, and other factors,
the wait time varies. The driver will attempt to read back the
values readattempts number of times. The default is 40 which
should be enough for most purposes. There is an initial wait of
10,500 microseconds followed by a additional 1,000 microseconds
per read attempt.
SEE ALSO
envsys(4), iic(4), envstat(8), sysctl(8)
HISTORY
The si70xxtemp driver first appeared in NetBSD 8.0.
AUTHORS
The si70xxtemp driver was written by Brad Spencer
<
[email protected]>.
FreeBSD 14.1-RELEASE-p8 December 28, 2017 FreeBSD 14.1-RELEASE-p8