xref: /freebsd-src/share/man/man4/lm75.4 (revision fa9896e082a1046ff4fbc75fcba4d18d1f2efc19)

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.Dd December 26, 2017
.Dt LM75 4
.Os
.Sh NAME
.Nm lm75
.Nd lm75 i2c digital temperature sensor driver
.Sh SYNOPSIS
.Cd "device iic"
.Cd "device iicbus"
.Cd "device lm75"
.Sh DESCRIPTION
The
.Nm
driver provides access to sensor data and configuration over the
.Xr iicbus 4 .
.Pp
It provides an easy and simple way to check the functionality of an i2c bus
as it provides read and write access to the
.Nm
configuration register.
.Pp
The access to
.Nm
data is made via the
.Xr sysctl 8
interface:
.Bd -literal
dev.lm75.0.%desc: LM75 temperature sensor
dev.lm75.0.%driver: lm75
dev.lm75.0.%location: addr=0x49
dev.lm75.0.%pnpinfo: name=lm750 compat=national,lm75
dev.lm75.0.%parent: iicbus3
dev.lm75.0.temperature: 27.1C
dev.lm75.0.thyst: 75.0C
dev.lm75.0.tos: 80.0C
dev.lm75.0.faults: 1
dev.lm75.0.mode: comparator
dev.lm75.0.polarity: active-low
dev.lm75.0.shutdown: 0
.Ed
.Bl -tag -width ".Va dev.lm75.%d.temperature"
.It Va dev.lm75.%d.temperature
Is the read-only value of the current temperature read by the sensor.
.It Va dev.lm75.%d.thyst
Sets the hysteresis temperature.
Once the temperature gets over the overtemperature shutdown value (tos)
it needs to drop below the hysteresis temperature to disable the output
(interrupt) pin again.
.It Va dev.lm75.%d.tos
Sets the overtemperature shutdown value.
Once the temperature gets over this value the output pin will be enabled.
The way the output (interrupt) pin works, depends on the mode configuration.
.It Va dev.lm75.%d.faults
Is the number of faults that must occur consecutively to activate the
interrupt (output) pin.
It can be set to 1, 2, 4, and 6.
.It Va dev.lm75.%d.mode
Sets the operation mode for the sensor interrupt pin.
It can be set to 'comparator' (default) or 'interrupt'.
.It Va dev.lm75.%d.polarity
Sets the polarity of the sensor interrupt pin.
It can be set to 'active-low' (default) or 'active-high'.
Please note that the output pin is an open-drain output and it needs a
proper pull-up resistor to work.
.It Va dev.lm75.%d.shutdown
When set to '1' it shuts down the sensor.
The temperature conversion stops but the sensor remains with its i2c bus
active, i.e., it can be woken up by setting this option to '0' again.
.El
.Pp
Please check the
.Nm
datasheet for more details.
.Pp
When used together with
.Xr snmp_lm75 3
it allows the monitoring of
.Nm
temperature data over SNMP.
.Pp
The
.Nm
driver supports both the low and the high resolution models.
.Pp
The low resolution model (lm75) provides a 9 bit output with the LSB
representing 0.5C.
.Pp
The high resolution model (lm75a) provides an 11 bit output with the LSB
representing 0.125C.
.Pp
The driver tries to auto-detect the
.Nm
model, but the detection of some
.Nm
clones may not work reliably.
.Pp
On a
.Xr device.hints 5
based system, such as
.Li MIPS ,
these values are configurable for
.Nm :
.Bl -tag -width ".Va hint.lm75.%d.addr"
.It Va hint.lm75.%d.at
Is the
.Xr iicbus 4
you are attaching to.
.It Va hint.lm75.%d.addr
Is the
.Nm
i2c address on the
.Xr iicbus 4 .
.El
.Pp
On a
.Xr FDT 4
based system, such as
.Li ARM ,
the DTS part for a
.Nm
device usually looks like:
.Bd -literal
i2c {
	/* Properties describing the controller appear here. */
	...
	lm750@49 {
		compatible = "national,lm75";
		reg = <0x49>;
	};
};
.Ed
.Pp
Where:
.Bl -tag -width ".Va compatible"
.It Va compatible
Should always be set to "national,lm75".
.It Va reg
Indicates which 7-bit i2c address the
.Nm
is wired at.
.Nm
temperature sensors can be wired to 8 different addresses, allowing up to 8
sensors on the same
.Xr iicbus 4 .
.El
.Sh SEE ALSO
.Xr snmp_lm75 3 ,
.Xr fdt 4 ,
.Xr iic 4 ,
.Xr iicbus 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 11.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver and this manual page were written by
.An Luiz Otavio O Souza Aq Mt loos@FreeBSD.org .