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