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1Kernel driver lm78
2==================
3
4Supported chips:
5 * National Semiconductor LM78
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 LM78-J
11 Prefix: 'lm78-j'
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 * National Semiconductor LM79
16 Prefix: 'lm79'
17 Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
18 Datasheet: Publicly available at the National Semiconductor website
19 http://www.national.com/
20
21Author: Frodo Looijaard <frodol@dds.nl>
22
23Description
24-----------
25
26This driver implements support for the National Semiconductor LM78, LM78-J
27and LM79. They are described as 'Microprocessor System Hardware Monitors'.
28
29There is almost no difference between the three supported chips. Functionally,
30the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,
31which is used to report the lower voltages newer Pentium processors use.
32From here on, LM7* means either of these three types.
33
34The LM7* implements one temperature sensor, three fan rotation speed sensors,
35seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.
36
37Temperatures are measured in degrees Celsius. An alarm is triggered once
38when the Overtemperature Shutdown limit is crossed; it is triggered again
39as soon as it drops below the Hysteresis value. A more useful behavior
40can be found by setting the Hysteresis value to +127 degrees Celsius; in
41this case, alarms are issued during all the time when the actual temperature
42is above the Overtemperature Shutdown value. Measurements are guaranteed
43between -55 and +125 degrees, with a resolution of 1 degree.
44
45Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
46triggered if the rotation speed has dropped below a programmable limit. Fan
47readings can be divided by a programmable divider (1, 2, 4 or 8) to give
48the readings more range or accuracy. Not all RPM values can accurately be
49represented, so some rounding is done. With a divider of 2, the lowest
50representable value is around 2600 RPM.
51
52Voltage sensors (also known as IN sensors) report their values in volts.
53An alarm is triggered if the voltage has crossed a programmable minimum
54or maximum limit. Note that minimum in this case always means 'closest to
55zero'; this is important for negative voltage measurements. All voltage
56inputs can measure voltages between 0 and 4.08 volts, with a resolution
57of 0.016 volt.
58
59The VID lines encode the core voltage value: the voltage level your processor
60should work with. This is hardcoded by the mainboard and/or processor itself.
61It is a value in volts. When it is unconnected, you will often find the
62value 3.50 V here.
63
64In addition to the alarms described above, there are a couple of additional
65ones. There is a BTI alarm, which gets triggered when an external chip has
66crossed its limits. Usually, this is connected to all LM75 chips; if at
67least one crosses its limits, this bit gets set. The CHAS alarm triggers
68if your computer case is open. The FIFO alarms should never trigger; it
69indicates an internal error. The SMI_IN alarm indicates some other chip
70has triggered an SMI interrupt. As we do not use SMI interrupts at all,
71this condition usually indicates there is a problem with some other
72device.
73
74If an alarm triggers, it will remain triggered until the hardware register
75is read at least once. This means that the cause for the alarm may
76already have disappeared! Note that in the current implementation, all
77hardware registers are read whenever any data is read (unless it is less
78than 1.5 seconds since the last update). This means that you can easily
79miss once-only alarms.
80
81The LM7* only updates its values each 1.5 seconds; reading it more often
82will do no harm, but will return 'old' values.