1 Kernel driver lm78
2 ==================
3
4 Supported chips:
5 * National Semiconductor LM78 / LM78-J
6 Prefix: 'lm78'
7 Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
8 Datasheet: Publicly available at the National Semiconductor website
9 http://www.national.com/
10 * National Semiconductor LM79
11 Prefix: 'lm79'
12 Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
13 Datasheet: Publicly available at the National Semiconductor website
14 http://www.national.com/
15
16 Author: Frodo Looijaard <frodol@dds.nl>
17
18 Description
19 -----------
20
21 This driver implements support for the National Semiconductor LM78, LM78-J
22 and LM79. They are described as 'Microprocessor System Hardware Monitors'.
23
24 There is almost no difference between the three supported chips. Functionally,
25 the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,
26 which is used to report the lower voltages newer Pentium processors use.
27 From here on, LM7* means either of these three types.
28
29 The LM7* implements one temperature sensor, three fan rotation speed sensors,
30 seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.
31
32 Temperatures are measured in degrees Celsius. An alarm is triggered once
33 when the Overtemperature Shutdown limit is crossed; it is triggered again
34 as soon as it drops below the Hysteresis value. A more useful behavior
35 can be found by setting the Hysteresis value to +127 degrees Celsius; in
36 this case, alarms are issued during all the time when the actual temperature
37 is above the Overtemperature Shutdown value. Measurements are guaranteed
38 between -55 and +125 degrees, with a resolution of 1 degree.
39
40 Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
41 triggered if the rotation speed has dropped below a programmable limit. Fan
42 readings can be divided by a programmable divider (1, 2, 4 or 8) to give
43 the readings more range or accuracy. Not all RPM values can accurately be
44 represented, so some rounding is done. With a divider of 2, the lowest
45 representable value is around 2600 RPM.
46
47 Voltage sensors (also known as IN sensors) report their values in volts.
48 An alarm is triggered if the voltage has crossed a programmable minimum
49 or maximum limit. Note that minimum in this case always means 'closest to
50 zero'; this is important for negative voltage measurements. All voltage
51 inputs can measure voltages between 0 and 4.08 volts, with a resolution
52 of 0.016 volt.
53
54 The VID lines encode the core voltage value: the voltage level your processor
55 should work with. This is hardcoded by the mainboard and/or processor itself.
56 It is a value in volts. When it is unconnected, you will often find the
57 value 3.50 V here.
58
59 In addition to the alarms described above, there are a couple of additional
60 ones. There is a BTI alarm, which gets triggered when an external chip has
61 crossed its limits. Usually, this is connected to all LM75 chips; if at
62 least one crosses its limits, this bit gets set. The CHAS alarm triggers
63 if your computer case is open. The FIFO alarms should never trigger; it
64 indicates an internal error. The SMI_IN alarm indicates some other chip
65 has triggered an SMI interrupt. As we do not use SMI interrupts at all,
66 this condition usually indicates there is a problem with some other
67 device.
68
69 If an alarm triggers, it will remain triggered until the hardware register
70 is read at least once. This means that the cause for the alarm may
71 already have disappeared! Note that in the current implementation, all
72 hardware registers are read whenever any data is read (unless it is less
73 than 1.5 seconds since the last update). This means that you can easily
74 miss once-only alarms.
75
76 The LM7* only updates its values each 1.5 seconds; reading it more often
77 will do no harm, but will return 'old' values.
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