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HTU21(4) FreeBSD Kernel Interfaces Manual HTU21(4)
NAME
htu21 - driver for HTU21D and compatible temperature and humidity sensors
SYNOPSIS
To compile this driver into the kernel, place the following lines in your
kernel configuration file:
device htu21
device iicbus
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
htu21_load="YES"
DESCRIPTION
The htu21 driver provides temperature and relative humidity readings over
I2C bus for the supported sensors:
o HTU21D
o SHT21
o Si7021
The htu21 driver reports data via sysctl(8) entries in the device's node
in the sysctl(8) tree:
temperature The temperature, in hundredths of Kelvin.
humidity The relative humidity, in hundredths of a percent.
crc_errors The number of CRC errors in reading the measurements from
the device.
power The good power indication. This can be useful with battery
powered sensors.
heater The built-in heater control. The heater can be used for
testing and for recovery from saturation after high
humidity.
hold_bus Whether the sensor should hold SCL low while performing the
measurement. Normally, the sensor releases the bus and
NACKs all accessed until the measurement is completed. The
hold mode may be useful in mult-master environments.
On an FDT(4) based system the following properties must be set:
compatible Must be set to "meas,htu21".
reg The I2C address of htu21. Although, it is hard-wired to 0x40
(7-bit) on all supported sensors.
The DTS part for a htu21 device usually looks like:
/ {
...
htu21d {
HISTORY
The htu21 driver and this manual page was written by Andriy Gapon
<avg@FreeBSD.org>.
BUGS
There is no way to control the measurement resolution.
Some sensor variants do not provide a serial number or use an
incompatible format. The htu21 driver does not distinguish those
variants and may complain about incorrect serial number checksum.
FreeBSD 14.0-RELEASE-p6 January 19, 2021 FreeBSD 14.0-RELEASE-p6