192 lines
5.0 KiB
Groff
192 lines
5.0 KiB
Groff
.\"
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.\" Copyright (c) 2014 Luiz Otavio O Souza <loos@freebsd.org>
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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. 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 ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 11, 2014
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.Dt LM75 4
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.Os
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.Sh NAME
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.Nm lm75
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.Nd lm75 i2c digital temperature sensor driver
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.Sh SYNOPSIS
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.Cd "device iic"
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.Cd "device iicbus"
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.Cd "device lm75"
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.Sh DESCRIPTION
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The
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.Nm
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driver provides access to sensor data and configuration over the
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.Xr iicbus 4 .
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.Pp
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It provides an easy and simple way to check the functionality of an i2c bus
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as it provides read and write access to the
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.Nm
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configuration register.
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.Pp
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The access to
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.Nm
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data is made via the
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.Xr sysctl 8
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interface:
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.Bd -literal
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dev.lm75.0.%desc: LM75 temperature sensor
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dev.lm75.0.%driver: lm75
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dev.lm75.0.%location: addr=0x49
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dev.lm75.0.%pnpinfo: name=lm750 compat=national,lm75
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dev.lm75.0.%parent: iicbus3
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dev.lm75.0.temperature: 27.1C
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dev.lm75.0.thyst: 75.0C
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dev.lm75.0.tos: 80.0C
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dev.lm75.0.faults: 1
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dev.lm75.0.mode: comparator
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dev.lm75.0.polarity: active-low
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dev.lm75.0.shutdown: 0
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.Ed
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.Bl -tag -width ".Va dev.lm75.%d.temperature"
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.It Va dev.lm75.%d.temperature
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Is the read-only value of the current temperature read by the sensor.
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.It Va dev.lm75.%d.thyst
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Sets the hysteresis temperature.
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Once the temperature gets over the overtemperature shutdown value (tos)
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it needs to drop below the hysteresis temperature to disable the output
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(interrupt) pin again.
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.It Va dev.lm75.%d.tos
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Sets the overtemperature shutdown value.
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Once the temperature gets over this value the output pin will be enabled.
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The way the output (interrupt) pin works, depends on the mode configuration.
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.It Va dev.lm75.%d.faults
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Is the number of faults that must occur consecutively to activate the
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interrupt (output) pin.
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It can be set to 1, 2, 4, and 6.
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.It Va dev.lm75.%d.mode
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Sets the operation mode for the sensor interrupt pin.
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It can be set to 'comparator' (default) or 'interrupt'.
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.It Va dev.lm75.%d.polarity
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Sets the polarity of the sensor interrupt pin.
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It can be set to 'active-low' (default) or 'active-high'.
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Please note that the output pin is an open-drain output and it needs a
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proper pull-up resistor to work.
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.It Va dev.lm75.%d.shutdown
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When set to '1' it shuts down the sensor.
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The temperature conversion stops but the sensor remains with its i2c bus
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active, i.e., it can be woken up by setting this option to '0' again.
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.El
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.Pp
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Please check the
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.Nm
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datasheet for more details.
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.Pp
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When used together with
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.Xr snmp_lm75 3
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it allows the monitoring of
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.Nm
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temperature data over SNMP.
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.Pp
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The
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.Nm
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driver supports both the low and the high resolution models.
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.Pp
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The low resolution model (lm75) provides a 9 bit output with the LSB
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representing 0.5C.
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.Pp
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The high resolution model (lm75a) provides an 11 bit output with the LSB
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representing 0.125C.
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.Pp
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The driver tries to auto-detect the
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.Nm
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model, but the detection of some
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.Nm
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clones may not work reliably.
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.Pp
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On a
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.Xr device.hints 5
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based system, like
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.Li MIPS ,
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these values are configurable for
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.Nm :
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.Bl -tag -width ".Va hint.lm75.%d.addr"
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.It Va hint.lm75.%d.at
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Is the
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.Xr iicbus 4
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you are attaching to.
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.It Va hint.lm75.%d.addr
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Is the
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.Nm
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i2c address on the
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.Xr iicbus 4 .
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.El
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.Pp
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On a
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.Xr FDT 4
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based system, like
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.Li ARM ,
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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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i2c {
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...
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lm750 {
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compatible = "national,lm75";
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i2c-address = <0x49>;
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};
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};
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.Ed
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.Pp
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Where:
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.Bl -tag -width ".Va i2c-address"
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.It Va compatible
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Should always be set to "national,lm75".
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.It Va i2c-address
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The
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.Va i2c-address
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property indicates which i2c address the
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.Nm
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is wired at.
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.Nm
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temperature sensors can be wired to 8 different addresses, allowing up to 8
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sensors on the same
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.Xr iicbus 4 .
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.El
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.Sh SEE ALSO
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.Xr snmp_lm75 3 ,
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.Xr fdt 4 ,
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.Xr iic 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 first appeared in
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.Fx 11.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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driver and this manual page were written by
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.An Luiz Otavio O Souza Aq loos@FreeBSD.org .
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