156 lines
4.6 KiB
Groff
156 lines
4.6 KiB
Groff
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.\"
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.\" Copyright (c) 2015 M. Warner Losh
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.\" All rights reserved.
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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. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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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 July 20, 2015
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.Dt OW_TEMP 4
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.Os
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.Sh NAME
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.Nm ow_temp
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.Nd Dallas Semiconductor 1-Wire Temperature sensor
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.Sh SYNOPSIS
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.Cd device ow_temp
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.Sh DESCRIPTION
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The
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.Nm
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module supports many of the 1-Wire temperature sensors.
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.Pp
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The sensor is read periodically and the results returned via a
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.Xr sysctl 3
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as described below.
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.Sh HARDWARE
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These temperature sensors are supported by the
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.Nm
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driver:
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.Bl -tag -width MAX31820 -compact
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.It DS1820
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1-Wire Digital Thermometer
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.It DS18S20
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High-Precision 1-Wire Digital Thermometer
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.It DS18B20
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Programmable Resolution 1-Wire Digital Thermometer
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.It DS1822
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Econo 1-Wire Digital Thermometer
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.It DS1825
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Programmable Resolution 1-Wire Digital Thermometer with 4-bit ID
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.It MAX31820
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1-Wire, Parasite-Power, Ambient Temperature Sensor
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.El
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.Pp
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The driver supports Family codes 0x10, 0x22, 0x28, and 0x3b.
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.Sh SYSCTL
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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 xxxxxxxxxx
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.It temperature
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The last temperature read, in milli-Kelvin.
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.It badcrc
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The number of CRC errors in reading the temperature form the
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device.
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Some CRC errors are to be expected.
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High rates of CRC errors, however, generally indicate a noisy
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environment, cabling issues, or too many devices on the bus.
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.It badread
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The number of times a non-CRC error was encountered reading the temperature
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from the card.
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This type of error is very rare.
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.It reading_interval
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The time, in ticks, between successive reads of the sensor.
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.It parasite
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This item is non-zero when the device is connected using its parasitic
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power mode.
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It can also indicate a wiring error.
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.El
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.Pp
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Temperatures are reported in milli-Kelvin, even though the absolute
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accuracy is around 0.2 degrees for the good devices and around 1
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degree for cheaper devices.
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The devices report in steps of 0.0625 degrees.
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The driver preserves the precision of the device's measurements
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in its
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.Xr sysctl 8
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reports.
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These devices often have a much higher relative accuracy and
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repeatability than their absolute accuracy.
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This makes them well suited for control loops that strive for
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stability and become possible if the full precision is preserved.
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.Sh SEE ALSO
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.Xr ow 4 ,
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.Xr owc 4 ,
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.Xr sysctl 8 ,
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.Xr owll 9 ,
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.Xr own 9
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.Sh LEGAL
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.Tn 1-Wire
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is a registered trademark of Maxim Integrated Products, Inc.
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 11.0 .
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.Sh AUTHORS
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The
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.Nm
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device driver and this manual page were written by
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.An Warner Losh .
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.Sh BUGS
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The parasitic mode of the devices does not work.
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It requires support from the
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.Xr owc 4
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driver that is unimplemented.
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.Pp
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The ID bits from the
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.Em DS1825
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are not recognized or reported.
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.Pp
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The type of the device is not reported via
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.Xr sysctl 8 .
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.Pp
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Alarm mode is not supported.
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It is not possible to set the low and high alarm temperatures.
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.Pp
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There is no way to write to the EEPROM.
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.Pp
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.Dq Convert Temperature
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requests are sent directly to the device.
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There is no way to use the broadcast ability of the 1-Wire bus to do
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all the conversions in parallel.
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.Pp
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It is not possible to set the precision on those devices that support
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it.
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.Pp
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The time to convert is fixed at 1 second, even though some devices are
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faster.
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.Pp
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There is no character device to supply a stream of readings to a
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program.
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Programs interested in the temperature must poll the sysctl to get the
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temperature.
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