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R.Marek@sh.cvut.cz7f15b662005-05-26 12:42:19 +00001Kernel driver lm80
2==================
3
4Supported 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/
10
11Authors:
12 Frodo Looijaard <frodol@dds.nl>,
13 Philip Edelbrock <phil@netroedge.com>
14
15Description
16-----------
17
18This driver implements support for the National Semiconductor LM80.
19It is described as a 'Serial Interface ACPI-Compatible Microprocessor
20System Hardware Monitor'.
21
22The LM80 implements one temperature sensor, two fan rotation speed sensors,
23seven voltage sensors, alarms, and some miscellaneous stuff.
24
25Temperatures are measured in degrees Celsius. There are two sets of limits
26which operate independently. When the HOT Temperature Limit is crossed,
27this will cause an alarm that will be reasserted until the temperature
28drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
29should work in the same way (but this must be checked; the datasheet
30is unclear about this). Measurements are guaranteed between -55 and
31+125 degrees. The current temperature measurement has a resolution of
320.0625 degrees; the limits have a resolution of 1 degree.
33
34Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
35triggered if the rotation speed has dropped below a programmable limit. Fan
36readings can be divided by a programmable divider (1, 2, 4 or 8) to give
37the readings more range or accuracy. Not all RPM values can accurately be
38represented, so some rounding is done. With a divider of 2, the lowest
39representable value is around 2600 RPM.
40
41Voltage sensors (also known as IN sensors) report their values in volts.
42An alarm is triggered if the voltage has crossed a programmable minimum
43or maximum limit. Note that minimum in this case always means 'closest to
44zero'; this is important for negative voltage measurements. All voltage
45inputs can measure voltages between 0 and 2.55 volts, with a resolution
46of 0.01 volt.
47
48If an alarm triggers, it will remain triggered until the hardware register
49is read at least once. This means that the cause for the alarm may
50already have disappeared! Note that in the current implementation, all
51hardware registers are read whenever any data is read (unless it is less
52than 2.0 seconds since the last update). This means that you can easily
53miss once-only alarms.
54
55The LM80 only updates its values each 1.5 seconds; reading it more often
56will do no harm, but will return 'old' values.