FreeBSD Manual Pages
HTU21(4) BSD Kernel Interfaces Manual HTU21(4) NAME htu21 -- driver for HTU21D and compatible temperature and humidity sen- sors 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 humid- ity. 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 { compatible = "meas,htu21"; reg = <0x40>; }; }; SEE ALSO fdt(4), iicbus(4), sysctl(8) HISTORY The htu21 driver and this manual page was written by Andriy Gapon <avg@FreeBSD.org>. BUGS There is no way to control the measurment resolution. Some sensor variants do not provide a serial number or use an incompati- ble format. The htu21 driver does not distinguish those variants and may complain about incorrect serial number checksum. BSD January 19, 2021 BSD
NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | BUGS
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=htu21&sektion=4&manpath=FreeBSD+13.0-RELEASE+and+Ports>