135 lines
3.6 KiB
Groff
135 lines
3.6 KiB
Groff
.\"
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.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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.\"
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.\" Copyright (c) 2021 Andriy Gapon <avg@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 19, 2021
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.Dt HTU21 4
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.Os
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.Sh NAME
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.Nm htu21
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.Nd driver for HTU21D and compatible temperature and humidity sensors
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following lines in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device htu21"
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.Cd "device iicbus"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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htu21_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver provides temperature and relative humidity readings over I2C bus
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for the supported sensors:
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.Bl -bullet -compact
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.It
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HTU21D
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.It
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SHT21
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.It
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Si7021
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.El
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.Pp
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The
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.Nm
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driver reports data via
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.Xr sysctl 8
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entries in the device's node in the
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.Xr sysctl 8
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tree:
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.Bl -tag -width temperature
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.It temperature
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The temperature, in hundredths of Kelvin.
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.It humidity
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The relative humidity, in hundredths of a percent.
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.It crc_errors
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The number of CRC errors in reading the measurements from the device.
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.It power
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The good power indication.
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This can be useful with battery powered sensors.
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.It heater
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The built-in heater control.
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The heater can be used for testing and for recovery from saturation
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after high humidity.
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.It hold_bus
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Whether the sensor should hold SCL low while performing the measurement.
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Normally, the sensor releases the bus and NACKs all accessed until the
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measurement is completed.
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The hold mode may be useful in mult-master environments.
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.El
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.Pp
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On an
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.Xr FDT 4
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based system the following properties must be set:
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.Bl -tag -width "compatible"
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.It Va compatible
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Must be set to "meas,htu21".
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.It Va reg
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The I2C address of
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.Nm .
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Although, it is hard-wired to 0x40 (7-bit) on all supported sensors.
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.El
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.Pp
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The DTS part for a
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.Nm
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device usually looks like:
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.Bd -literal
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/ {
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...
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htu21d {
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compatible = "meas,htu21";
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reg = <0x40>;
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};
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};
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.Ed
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.Sh SEE ALSO
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.Xr fdt 4 ,
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.Xr iicbus 4 ,
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.Xr sysctl 8
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.Sh HISTORY
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The
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.Nm
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driver and this manual page was written by
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.An Andriy Gapon Aq Mt avg@FreeBSD.org .
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.Sh BUGS
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There is no way to control the measurment resolution.
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.Pp
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Some sensor variants do not provide a serial number or use an incompatible
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format.
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The
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.Nm
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driver does not distinguish those variants and may complain about incorrect
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serial number checksum.
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