Manual Pages  — HTU21

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

htu21_load="YES"

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 {
                compatible = "meas,htu21";
                reg = <0x40>;
        };
};