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)
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