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34 .Nd driver for HTU21D and compatible temperature and humidity sensors
36 To compile this driver into the kernel,
37 place the following lines in your
38 kernel configuration file:
39 .Bd -ragged -offset indent
44 Alternatively, to load the driver as a
45 module at boot time, place the following line in
47 .Bd -literal -offset indent
53 driver provides temperature and relative humidity readings over I2C bus
54 for the supported sensors:
66 driver reports data via
68 entries in the device's node in the
71 .Bl -tag -width temperature
73 The temperature, in hundredths of Kelvin.
75 The relative humidity, in hundredths of a percent.
77 The number of CRC errors in reading the measurements from the device.
79 The good power indication.
80 This can be useful with battery powered sensors.
82 The built-in heater control.
83 The heater can be used for testing and for recovery from saturation
86 Whether the sensor should hold SCL low while performing the measurement.
87 Normally, the sensor releases the bus and NACKs all accessed until the
88 measurement is completed.
89 The hold mode may be useful in mult-master environments.
94 based system the following properties must be set:
95 .Bl -tag -width "compatible"
97 Must be set to "meas,htu21".
101 Although, it is hard-wired to 0x40 (7-bit) on all supported sensors.
106 device usually looks like:
112 compatible = "meas,htu21";
124 driver and this manual page was written by
125 .An Andriy Gapon Aq Mt avg@FreeBSD.org .
127 There is no way to control the measurment resolution.
129 Some sensor variants do not provide a serial number or use an incompatible
133 driver does not distinguish those variants and may complain about incorrect
134 serial number checksum.