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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/ | |
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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. |