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Commit | Line | Data |
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7f15b664 RM |
1 | Kernel driver lm78 |
2 | ================== | |
3 | ||
4 | Supported 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 | ||
21 | Author: Frodo Looijaard <frodol@dds.nl> | |
22 | ||
23 | Description | |
24 | ----------- | |
25 | ||
26 | This driver implements support for the National Semiconductor LM78, LM78-J | |
27 | and LM79. They are described as 'Microprocessor System Hardware Monitors'. | |
28 | ||
29 | There is almost no difference between the three supported chips. Functionally, | |
30 | the LM78 and LM78-J are exactly identical. The LM79 has one more VID line, | |
31 | which is used to report the lower voltages newer Pentium processors use. | |
32 | From here on, LM7* means either of these three types. | |
33 | ||
34 | The LM7* implements one temperature sensor, three fan rotation speed sensors, | |
35 | seven voltage sensors, VID lines, alarms, and some miscellaneous stuff. | |
36 | ||
37 | Temperatures are measured in degrees Celsius. An alarm is triggered once | |
38 | when the Overtemperature Shutdown limit is crossed; it is triggered again | |
39 | as soon as it drops below the Hysteresis value. A more useful behavior | |
40 | can be found by setting the Hysteresis value to +127 degrees Celsius; in | |
41 | this case, alarms are issued during all the time when the actual temperature | |
42 | is above the Overtemperature Shutdown value. Measurements are guaranteed | |
43 | between -55 and +125 degrees, with a resolution of 1 degree. | |
44 | ||
45 | Fan rotation speeds are reported in RPM (rotations per minute). An alarm is | |
46 | triggered if the rotation speed has dropped below a programmable limit. Fan | |
47 | readings can be divided by a programmable divider (1, 2, 4 or 8) to give | |
48 | the readings more range or accuracy. Not all RPM values can accurately be | |
49 | represented, so some rounding is done. With a divider of 2, the lowest | |
50 | representable value is around 2600 RPM. | |
51 | ||
52 | Voltage sensors (also known as IN sensors) report their values in volts. | |
53 | An alarm is triggered if the voltage has crossed a programmable minimum | |
54 | or maximum limit. Note that minimum in this case always means 'closest to | |
55 | zero'; this is important for negative voltage measurements. All voltage | |
56 | inputs can measure voltages between 0 and 4.08 volts, with a resolution | |
57 | of 0.016 volt. | |
58 | ||
59 | The VID lines encode the core voltage value: the voltage level your processor | |
60 | should work with. This is hardcoded by the mainboard and/or processor itself. | |
61 | It is a value in volts. When it is unconnected, you will often find the | |
62 | value 3.50 V here. | |
63 | ||
64 | In addition to the alarms described above, there are a couple of additional | |
65 | ones. There is a BTI alarm, which gets triggered when an external chip has | |
66 | crossed its limits. Usually, this is connected to all LM75 chips; if at | |
67 | least one crosses its limits, this bit gets set. The CHAS alarm triggers | |
68 | if your computer case is open. The FIFO alarms should never trigger; it | |
69 | indicates an internal error. The SMI_IN alarm indicates some other chip | |
70 | has triggered an SMI interrupt. As we do not use SMI interrupts at all, | |
71 | this condition usually indicates there is a problem with some other | |
72 | device. | |
73 | ||
74 | If an alarm triggers, it will remain triggered until the hardware register | |
75 | is read at least once. This means that the cause for the alarm may | |
76 | already have disappeared! Note that in the current implementation, all | |
77 | hardware registers are read whenever any data is read (unless it is less | |
78 | than 1.5 seconds since the last update). This means that you can easily | |
79 | miss once-only alarms. | |
80 | ||
81 | The LM7* only updates its values each 1.5 seconds; reading it more often | |
82 | will do no harm, but will return 'old' values. |