1.\" 2.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3.\" 4.\" Copyright (c) 2021 Andriy Gapon <avg@FreeBSD.org> 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" $FreeBSD$ 28.\" 29.Dd January 19, 2021 30.Dt HTU21 4 31.Os 32.Sh NAME 33.Nm htu21 34.Nd driver for HTU21D and compatible temperature and humidity sensors 35.Sh SYNOPSIS 36To compile this driver into the kernel, 37place the following lines in your 38kernel configuration file: 39.Bd -ragged -offset indent 40.Cd "device htu21" 41.Cd "device iicbus" 42.Ed 43.Pp 44Alternatively, to load the driver as a 45module at boot time, place the following line in 46.Xr loader.conf 5 : 47.Bd -literal -offset indent 48htu21_load="YES" 49.Ed 50.Sh DESCRIPTION 51The 52.Nm 53driver provides temperature and relative humidity readings over I2C bus 54for the supported sensors: 55.Bl -bullet -compact 56.It 57HTU21D 58.It 59SHT21 60.It 61Si7021 62.El 63.Pp 64The 65.Nm 66driver reports data via 67.Xr sysctl 8 68entries in the device's node in the 69.Xr sysctl 8 70tree: 71.Bl -tag -width temperature 72.It temperature 73The temperature, in hundredths of Kelvin. 74.It humidity 75The relative humidity, in hundredths of a percent. 76.It crc_errors 77The number of CRC errors in reading the measurements from the device. 78.It power 79The good power indication. 80This can be useful with battery powered sensors. 81.It heater 82The built-in heater control. 83The heater can be used for testing and for recovery from saturation 84after high humidity. 85.It hold_bus 86Whether the sensor should hold SCL low while performing the measurement. 87Normally, the sensor releases the bus and NACKs all accessed until the 88measurement is completed. 89The hold mode may be useful in mult-master environments. 90.El 91.Pp 92On an 93.Xr FDT 4 94based system the following properties must be set: 95.Bl -tag -width "compatible" 96.It Va compatible 97Must be set to "meas,htu21". 98.It Va reg 99The I2C address of 100.Nm . 101Although, it is hard-wired to 0x40 (7-bit) on all supported sensors. 102.El 103.Pp 104The DTS part for a 105.Nm 106device usually looks like: 107.Bd -literal 108/ { 109 110 ... 111 htu21d { 112 compatible = "meas,htu21"; 113 reg = <0x40>; 114 }; 115}; 116.Ed 117.Sh SEE ALSO 118.Xr fdt 4 , 119.Xr iicbus 4 , 120.Xr sysctl 8 121.Sh HISTORY 122The 123.Nm 124driver and this manual page was written by 125.An Andriy Gapon Aq Mt avg@FreeBSD.org . 126.Sh BUGS 127There is no way to control the measurment resolution. 128.Pp 129Some sensor variants do not provide a serial number or use an incompatible 130format. 131The 132.Nm 133driver does not distinguish those variants and may complain about incorrect 134serial number checksum. 135