| R.Marek@sh.cvut.cz | 7f15b66 | 2005-05-26 12:42:19 +0000 | [diff] [blame] | 1 | Kernel driver lm80 |
| 2 | ================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * National Semiconductor LM80 |
| 6 | Prefix: 'lm80' |
| 7 | Addresses scanned: I2C 0x28 - 0x2f |
| 8 | Datasheet: Publicly available at the National Semiconductor website |
| 9 | http://www.national.com/ |
| 10 | |
| 11 | Authors: |
| 12 | Frodo Looijaard <frodol@dds.nl>, |
| 13 | Philip Edelbrock <phil@netroedge.com> |
| 14 | |
| 15 | Description |
| 16 | ----------- |
| 17 | |
| 18 | This driver implements support for the National Semiconductor LM80. |
| 19 | It is described as a 'Serial Interface ACPI-Compatible Microprocessor |
| 20 | System Hardware Monitor'. |
| 21 | |
| 22 | The LM80 implements one temperature sensor, two fan rotation speed sensors, |
| 23 | seven voltage sensors, alarms, and some miscellaneous stuff. |
| 24 | |
| 25 | Temperatures are measured in degrees Celsius. There are two sets of limits |
| 26 | which operate independently. When the HOT Temperature Limit is crossed, |
| 27 | this will cause an alarm that will be reasserted until the temperature |
| 28 | drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits |
| 29 | should work in the same way (but this must be checked; the datasheet |
| 30 | is unclear about this). Measurements are guaranteed between -55 and |
| 31 | +125 degrees. The current temperature measurement has a resolution of |
| 32 | 0.0625 degrees; the limits have a resolution of 1 degree. |
| 33 | |
| 34 | Fan rotation speeds are reported in RPM (rotations per minute). An alarm is |
| 35 | triggered if the rotation speed has dropped below a programmable limit. Fan |
| 36 | readings can be divided by a programmable divider (1, 2, 4 or 8) to give |
| 37 | the readings more range or accuracy. Not all RPM values can accurately be |
| 38 | represented, so some rounding is done. With a divider of 2, the lowest |
| 39 | representable value is around 2600 RPM. |
| 40 | |
| 41 | Voltage sensors (also known as IN sensors) report their values in volts. |
| 42 | An alarm is triggered if the voltage has crossed a programmable minimum |
| 43 | or maximum limit. Note that minimum in this case always means 'closest to |
| 44 | zero'; this is important for negative voltage measurements. All voltage |
| 45 | inputs can measure voltages between 0 and 2.55 volts, with a resolution |
| 46 | of 0.01 volt. |
| 47 | |
| 48 | If an alarm triggers, it will remain triggered until the hardware register |
| 49 | is read at least once. This means that the cause for the alarm may |
| 50 | already have disappeared! Note that in the current implementation, all |
| 51 | hardware registers are read whenever any data is read (unless it is less |
| 52 | than 2.0 seconds since the last update). This means that you can easily |
| 53 | miss once-only alarms. |
| 54 | |
| 55 | The LM80 only updates its values each 1.5 seconds; reading it more often |
| 56 | will do no harm, but will return 'old' values. |