OpenBSD manual page server

Manual Page Search Parameters

LM(4) Device Drivers Manual LM(4)

lmNational Semiconductor LM78/79/81 temperature, voltage, and fan sensor

lm0 at isa? port 0x290
lm1 at isa? port 0x280
lm2 at isa? port 0x310
lm* at iic?
lm* at wbsio?

The lm driver provides support for the National Semiconductor LM78/79/81 hardware monitors and register compatible chips to be used with the sysctl(8) interface.

The original LM78 hardware monitor supports 11 sensors:

uV DC Core voltage
uV DC Unknown
uV DC +3.3V
uV DC +5V
uV DC +12V
uV DC -12V
uV DC -5V
uK Motherboard Temperature
RPM Chassis Fan

For other devices, sensors' names and numbers will be different.

Chips supported by the lm driver include:

Some devices can attach to both iic(4) and isa(4); others can only attach to either one or the other. If the lm driver detects a device attaching to both iic(4) and isa(4), it will detach the device from iic(4).

iic(4), isa(4), wbsio(4), sensorsd(8), sysctl(8)

The lm driver first appeared in NetBSD 1.5; OpenBSD support was added in OpenBSD 3.4.

The lm driver was written by Bill Squier and ported to OpenBSD 3.4 by Alexander Yurchenko <>. The driver was largely rewritten for OpenBSD 3.9 by Mark Kettenis <>.

Some vendors connect these chips to non-standard thermal diodes and resistors. This will result in bogus sensor values.

Interrupt support is unimplemented.

There are currently no known pnpbios IDs assigned to LM chips.

This driver attaches to the Winbond W83791SD chip even though that chip does not have any sensors.

December 17, 2019 OpenBSD-current