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1 | Kernel driver lm87 | ||
2 | ================== | ||
3 | |||
4 | Supported chips: | ||
5 | * National Semiconductor LM87 | ||
6 | Prefix: 'lm87' | ||
7 | Addresses scanned: I2C 0x2c - 0x2f | ||
8 | Datasheet: http://www.national.com/pf/LM/LM87.html | ||
9 | |||
10 | Authors: | ||
11 | Frodo Looijaard <frodol@dds.nl>, | ||
12 | Philip Edelbrock <phil@netroedge.com>, | ||
13 | Mark Studebaker <mdsxyz123@yahoo.com>, | ||
14 | Stephen Rousset <stephen.rousset@rocketlogix.com>, | ||
15 | Dan Eaton <dan.eaton@rocketlogix.com>, | ||
16 | Jean Delvare <khali@linux-fr.org>, | ||
17 | Original 2.6 port Jeff Oliver | ||
18 | |||
19 | Description | ||
20 | ----------- | ||
21 | |||
22 | This driver implements support for the National Semiconductor LM87. | ||
23 | |||
24 | The LM87 implements up to three temperature sensors, up to two fan | ||
25 | rotation speed sensors, up to seven voltage sensors, alarms, and some | ||
26 | miscellaneous stuff. | ||
27 | |||
28 | Temperatures are measured in degrees Celsius. Each input has a high | ||
29 | and low alarm settings. A high limit produces an alarm when the value | ||
30 | goes above it, and an alarm is also produced when the value goes below | ||
31 | the low limit. | ||
32 | |||
33 | Fan rotation speeds are reported in RPM (rotations per minute). An alarm is | ||
34 | triggered if the rotation speed has dropped below a programmable limit. Fan | ||
35 | readings can be divided by a programmable divider (1, 2, 4 or 8) to give | ||
36 | the readings more range or accuracy. Not all RPM values can accurately be | ||
37 | represented, so some rounding is done. With a divider of 2, the lowest | ||
38 | representable value is around 2600 RPM. | ||
39 | |||
40 | Voltage sensors (also known as IN sensors) report their values in | ||
41 | volts. An alarm is triggered if the voltage has crossed a programmable | ||
42 | minimum or maximum limit. Note that minimum in this case always means | ||
43 | 'closest to zero'; this is important for negative voltage measurements. | ||
44 | |||
45 | If an alarm triggers, it will remain triggered until the hardware register | ||
46 | is read at least once. This means that the cause for the alarm may | ||
47 | already have disappeared! Note that in the current implementation, all | ||
48 | hardware registers are read whenever any data is read (unless it is less | ||
49 | than 1.0 seconds since the last update). This means that you can easily | ||
50 | miss once-only alarms. | ||
51 | |||
52 | The lm87 driver only updates its values each 1.0 seconds; reading it more | ||
53 | often will do no harm, but will return 'old' values. | ||
54 | |||
55 | |||
56 | Hardware Configurations | ||
57 | ----------------------- | ||
58 | |||
59 | The LM87 has four pins which can serve one of two possible functions, | ||
60 | depending on the hardware configuration. | ||
61 | |||
62 | Some functions share pins, so not all functions are available at the same | ||
63 | time. Which are depends on the hardware setup. This driver assumes that | ||
64 | the BIOS configured the chip correctly. In that respect, it differs from | ||
65 | the original driver (from lm_sensors for Linux 2.4), which would force the | ||
66 | LM87 to an arbitrary, compile-time chosen mode, regardless of the actual | ||
67 | chipset wiring. | ||
68 | |||
69 | For reference, here is the list of exclusive functions: | ||
70 | - in0+in5 (default) or temp3 | ||
71 | - fan1 (default) or in6 | ||
72 | - fan2 (default) or in7 | ||
73 | - VID lines (default) or IRQ lines (not handled by this driver) | ||