| Kernel driver lm80 |
| ================== |
| |
| Supported chips: |
| * National Semiconductor LM80 |
| Prefix: 'lm80' |
| Addresses scanned: I2C 0x28 - 0x2f |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/ |
| |
| Authors: |
| Frodo Looijaard <frodol@dds.nl>, |
| Philip Edelbrock <phil@netroedge.com> |
| |
| Description |
| ----------- |
| |
| This driver implements support for the National Semiconductor LM80. |
| It is described as a 'Serial Interface ACPI-Compatible Microprocessor |
| System Hardware Monitor'. |
| |
| The LM80 implements one temperature sensor, two fan rotation speed sensors, |
| seven voltage sensors, alarms, and some miscellaneous stuff. |
| |
| Temperatures are measured in degrees Celsius. There are two sets of limits |
| which operate independently. When the HOT Temperature Limit is crossed, |
| this will cause an alarm that will be reasserted until the temperature |
| drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits |
| should work in the same way (but this must be checked; the datasheet |
| is unclear about this). Measurements are guaranteed between -55 and |
| +125 degrees. The current temperature measurement has a resolution of |
| 0.0625 degrees; the limits have a resolution of 1 degree. |
| |
| Fan rotation speeds are reported in RPM (rotations per minute). An alarm is |
| triggered if the rotation speed has dropped below a programmable limit. Fan |
| readings can be divided by a programmable divider (1, 2, 4 or 8) to give |
| the readings more range or accuracy. Not all RPM values can accurately be |
| represented, so some rounding is done. With a divider of 2, the lowest |
| representable value is around 2600 RPM. |
| |
| Voltage sensors (also known as IN sensors) report their values in volts. |
| An alarm is triggered if the voltage has crossed a programmable minimum |
| or maximum limit. Note that minimum in this case always means 'closest to |
| zero'; this is important for negative voltage measurements. All voltage |
| inputs can measure voltages between 0 and 2.55 volts, with a resolution |
| of 0.01 volt. |
| |
| If an alarm triggers, it will remain triggered until the hardware register |
| is read at least once. This means that the cause for the alarm may |
| already have disappeared! Note that in the current implementation, all |
| hardware registers are read whenever any data is read (unless it is less |
| than 2.0 seconds since the last update). This means that you can easily |
| miss once-only alarms. |
| |
| The LM80 only updates its values each 1.5 seconds; reading it more often |
| will do no harm, but will return 'old' values. |