1.\" 2.\" SPDX-License-Identifier: BSD-2-Clause 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.Dd January 19, 2021 28.Dt HTU21 4 29.Os 30.Sh NAME 31.Nm htu21 32.Nd driver for HTU21D and compatible temperature and humidity sensors 33.Sh SYNOPSIS 34To compile this driver into the kernel, 35place the following lines in your 36kernel configuration file: 37.Bd -ragged -offset indent 38.Cd "device htu21" 39.Cd "device iicbus" 40.Ed 41.Pp 42Alternatively, to load the driver as a 43module at boot time, place the following line in 44.Xr loader.conf 5 : 45.Bd -literal -offset indent 46htu21_load="YES" 47.Ed 48.Sh DESCRIPTION 49The 50.Nm 51driver provides temperature and relative humidity readings over I2C bus 52for the supported sensors: 53.Bl -bullet -compact 54.It 55HTU21D 56.It 57SHT21 58.It 59Si7021 60.El 61.Pp 62The 63.Nm 64driver reports data via 65.Xr sysctl 8 66entries in the device's node in the 67.Xr sysctl 8 68tree: 69.Bl -tag -width temperature 70.It temperature 71The temperature, in hundredths of Kelvin. 72.It humidity 73The relative humidity, in hundredths of a percent. 74.It crc_errors 75The number of CRC errors in reading the measurements from the device. 76.It power 77The good power indication. 78This can be useful with battery powered sensors. 79.It heater 80The built-in heater control. 81The heater can be used for testing and for recovery from saturation 82after high humidity. 83.It hold_bus 84Whether the sensor should hold SCL low while performing the measurement. 85Normally, the sensor releases the bus and NACKs all accessed until the 86measurement is completed. 87The hold mode may be useful in mult-master environments. 88.El 89.Pp 90On an 91.Xr FDT 4 92based system the following properties must be set: 93.Bl -tag -width "compatible" 94.It Va compatible 95Must be set to "meas,htu21". 96.It Va reg 97The I2C address of 98.Nm . 99Although, it is hard-wired to 0x40 (7-bit) on all supported sensors. 100.El 101.Pp 102The DTS part for a 103.Nm 104device usually looks like: 105.Bd -literal 106/ { 107 108 ... 109 htu21d { 110 compatible = "meas,htu21"; 111 reg = <0x40>; 112 }; 113}; 114.Ed 115.Sh SEE ALSO 116.Xr fdt 4 , 117.Xr iicbus 4 , 118.Xr sysctl 8 119.Sh HISTORY 120The 121.Nm 122driver and this manual page was written by 123.An Andriy Gapon Aq Mt avg@FreeBSD.org . 124.Sh BUGS 125There is no way to control the measurement resolution. 126.Pp 127Some sensor variants do not provide a serial number or use an incompatible 128format. 129The 130.Nm 131driver does not distinguish those variants and may complain about incorrect 132serial number checksum. 133