[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / hwmon / lm80

Kernel driver lm80
==================

Supported chips:
  * National Semiconductor LM80
    Prefix: 'lm80'
    Addresses scanned: I2C 0x28 - 0x2f
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/
  * National Semiconductor LM96080
    Prefix: 'lm96080'
    Addresses scanned: I2C 0x28 - 0x2f
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/

Authors:
        Frodo Looijaard <frodol@dds.nl>,
        Philip Edelbrock <phil@netroedge.com>

Description
-----------

This driver implements support for the National Semiconductor LM80.
It is described as a 'Serial Interface ACPI-Compatible Microprocessor
System Hardware Monitor'. The LM96080 is a more recent incarnation,
it is pin and register compatible, with a few additional features not
yet supported by the driver.

The LM80 implements one temperature sensor, two fan rotation speed sensors,
seven voltage sensors, alarms, and some miscellaneous stuff.

Temperatures are measured in degrees Celsius. There are two sets of limits
which operate independently. When the HOT Temperature Limit is crossed,
this will cause an alarm that will be reasserted until the temperature
drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
should work in the same way (but this must be checked; the datasheet
is unclear about this). Measurements are guaranteed between -55 and
+125 degrees. The current temperature measurement has a resolution of
0.0625 degrees; the limits have a resolution of 1 degree.

Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
triggered if the rotation speed has dropped below a programmable limit. Fan
readings can be divided by a programmable divider (1, 2, 4 or 8) to give
the readings more range or accuracy. Not all RPM values can accurately be
represented, so some rounding is done. With a divider of 2, the lowest
representable value is around 2600 RPM.

Voltage sensors (also known as IN sensors) report their values in volts.
An alarm is triggered if the voltage has crossed a programmable minimum
or maximum limit. Note that minimum in this case always means 'closest to
zero'; this is important for negative voltage measurements. All voltage
inputs can measure voltages between 0 and 2.55 volts, with a resolution
of 0.01 volt.

If an alarm triggers, it will remain triggered until the hardware register
is read at least once. This means that the cause for the alarm may
already have disappeared! Note that in the current implementation, all
hardware registers are read whenever any data is read (unless it is less
than 2.0 seconds since the last update). This means that you can easily
miss once-only alarms.

The LM80 only updates its values each 1.5 seconds; reading it more often
will do no harm, but will return 'old' values.
Commit	Line	Data
7f15b664 RM	1	Kernel driver lm80
	2	==================
	3
	4	Supported chips:
	5	* National Semiconductor LM80
	6	Prefix: 'lm80'
	7	Addresses scanned: I2C 0x28 - 0x2f
	8	Datasheet: Publicly available at the National Semiconductor website
	9	http://www.national.com/
9908ad4c JD	10	* National Semiconductor LM96080
	11	Prefix: 'lm96080'
	12	Addresses scanned: I2C 0x28 - 0x2f
	13	Datasheet: Publicly available at the National Semiconductor website
	14	http://www.national.com/
7f15b664 RM	15
	16	Authors:
	17	Frodo Looijaard <frodol@dds.nl>,
	18	Philip Edelbrock <phil@netroedge.com>
	19
	20	Description
	21	-----------
	22
	23	This driver implements support for the National Semiconductor LM80.
	24	It is described as a 'Serial Interface ACPI-Compatible Microprocessor
9908ad4c JD	25	System Hardware Monitor'. The LM96080 is a more recent incarnation,
	26	it is pin and register compatible, with a few additional features not
	27	yet supported by the driver.
7f15b664 RM	28
	29	The LM80 implements one temperature sensor, two fan rotation speed sensors,
	30	seven voltage sensors, alarms, and some miscellaneous stuff.
	31
	32	Temperatures are measured in degrees Celsius. There are two sets of limits
	33	which operate independently. When the HOT Temperature Limit is crossed,
	34	this will cause an alarm that will be reasserted until the temperature
	35	drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
	36	should work in the same way (but this must be checked; the datasheet
	37	is unclear about this). Measurements are guaranteed between -55 and
	38	+125 degrees. The current temperature measurement has a resolution of
	39	0.0625 degrees; the limits have a resolution of 1 degree.
	40
	41	Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
	42	triggered if the rotation speed has dropped below a programmable limit. Fan
	43	readings can be divided by a programmable divider (1, 2, 4 or 8) to give
	44	the readings more range or accuracy. Not all RPM values can accurately be
	45	represented, so some rounding is done. With a divider of 2, the lowest
	46	representable value is around 2600 RPM.
	47
	48	Voltage sensors (also known as IN sensors) report their values in volts.
	49	An alarm is triggered if the voltage has crossed a programmable minimum
	50	or maximum limit. Note that minimum in this case always means 'closest to
	51	zero'; this is important for negative voltage measurements. All voltage
	52	inputs can measure voltages between 0 and 2.55 volts, with a resolution
	53	of 0.01 volt.
	54
	55	If an alarm triggers, it will remain triggered until the hardware register
	56	is read at least once. This means that the cause for the alarm may
	57	already have disappeared! Note that in the current implementation, all
	58	hardware registers are read whenever any data is read (unless it is less
	59	than 2.0 seconds since the last update). This means that you can easily
	60	miss once-only alarms.
	61
	62	The LM80 only updates its values each 1.5 seconds; reading it more often
	63	will do no harm, but will return 'old' values.