projects / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 7f15b664 RM |
1 | Kernel driver lm78 |
| 2 | ================== | |
| 3 | ||
| 4 | Supported chips: | |
| 27fe048e | 5 | * National Semiconductor LM78 / LM78-J |
| 7f15b664 | 6 | Prefix: 'lm78' |
| 6722fead | 7 | Addresses scanned: I2C 0x28 - 0x2f, ISA 0x290 (8 I/O ports) |
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8 | Datasheet: Publicly available at the National Semiconductor website |
| 9 | http://www.national.com/ | |
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10 | * National Semiconductor LM79 |
| 11 | Prefix: 'lm79' | |
| 6722fead | 12 | Addresses scanned: I2C 0x28 - 0x2f, ISA 0x290 (8 I/O ports) |
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13 | Datasheet: Publicly available at the National Semiconductor website |
| 14 | http://www.national.com/ | |
| 15 | ||
| 156e2d1a JD |
16 | Authors: Frodo Looijaard <[email protected]> |
| 17 | Jean Delvare <[email protected]> | |
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18 | |
| 19 | Description | |
| 20 | ----------- | |
| 21 | ||
| 22 | This driver implements support for the National Semiconductor LM78, LM78-J | |
| 23 | and LM79. They are described as 'Microprocessor System Hardware Monitors'. | |
| 24 | ||
| 25 | There is almost no difference between the three supported chips. Functionally, | |
| 26 | the LM78 and LM78-J are exactly identical. The LM79 has one more VID line, | |
| 27 | which is used to report the lower voltages newer Pentium processors use. | |
| 28 | From here on, LM7* means either of these three types. | |
| 29 | ||
| 30 | The LM7* implements one temperature sensor, three fan rotation speed sensors, | |
| 31 | seven voltage sensors, VID lines, alarms, and some miscellaneous stuff. | |
| 32 | ||
| 33 | Temperatures are measured in degrees Celsius. An alarm is triggered once | |
| 34 | when the Overtemperature Shutdown limit is crossed; it is triggered again | |
| 35 | as soon as it drops below the Hysteresis value. A more useful behavior | |
| 36 | can be found by setting the Hysteresis value to +127 degrees Celsius; in | |
| 37 | this case, alarms are issued during all the time when the actual temperature | |
| 38 | is above the Overtemperature Shutdown value. Measurements are guaranteed | |
| 39 | between -55 and +125 degrees, with a resolution of 1 degree. | |
| 40 | ||
| 41 | Fan rotation speeds are reported in RPM (rotations per minute). An alarm is | |
| 42 | triggered if the rotation speed has dropped below a programmable limit. Fan | |
| 43 | readings can be divided by a programmable divider (1, 2, 4 or 8) to give | |
| 44 | the readings more range or accuracy. Not all RPM values can accurately be | |
| 45 | represented, so some rounding is done. With a divider of 2, the lowest | |
| 46 | representable value is around 2600 RPM. | |
| 47 | ||
| 48 | Voltage sensors (also known as IN sensors) report their values in volts. | |
| 49 | An alarm is triggered if the voltage has crossed a programmable minimum | |
| 50 | or maximum limit. Note that minimum in this case always means 'closest to | |
| 51 | zero'; this is important for negative voltage measurements. All voltage | |
| 52 | inputs can measure voltages between 0 and 4.08 volts, with a resolution | |
| 53 | of 0.016 volt. | |
| 54 | ||
| 55 | The VID lines encode the core voltage value: the voltage level your processor | |
| 56 | should work with. This is hardcoded by the mainboard and/or processor itself. | |
| 57 | It is a value in volts. When it is unconnected, you will often find the | |
| 58 | value 3.50 V here. | |
| 59 | ||
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60 | If an alarm triggers, it will remain triggered until the hardware register |
| 61 | is read at least once. This means that the cause for the alarm may | |
| 62 | already have disappeared! Note that in the current implementation, all | |
| 63 | hardware registers are read whenever any data is read (unless it is less | |
| 64 | than 1.5 seconds since the last update). This means that you can easily | |
| 65 | miss once-only alarms. | |
| 66 | ||
| 67 | The LM7* only updates its values each 1.5 seconds; reading it more often | |
| 68 | will do no harm, but will return 'old' values. |