| Kernel driver lm78 | |
| ================== | |
| Supported chips: | |
| * National Semiconductor LM78 / LM78-J | |
| Prefix: 'lm78' | |
| Addresses scanned: I2C 0x28 - 0x2f, ISA 0x290 (8 I/O ports) | |
| Datasheet: Publicly available at the National Semiconductor website | |
| http://www.national.com/ | |
| * National Semiconductor LM79 | |
| Prefix: 'lm79' | |
| Addresses scanned: I2C 0x28 - 0x2f, ISA 0x290 (8 I/O ports) | |
| Datasheet: Publicly available at the National Semiconductor website | |
| http://www.national.com/ | |
| Authors: Frodo Looijaard <frodol@dds.nl> | |
| Jean Delvare <jdelvare@suse.de> | |
| Description | |
| ----------- | |
| This driver implements support for the National Semiconductor LM78, LM78-J | |
| and LM79. They are described as 'Microprocessor System Hardware Monitors'. | |
| There is almost no difference between the three supported chips. Functionally, | |
| the LM78 and LM78-J are exactly identical. The LM79 has one more VID line, | |
| which is used to report the lower voltages newer Pentium processors use. | |
| From here on, LM7* means either of these three types. | |
| The LM7* implements one temperature sensor, three fan rotation speed sensors, | |
| seven voltage sensors, VID lines, alarms, and some miscellaneous stuff. | |
| Temperatures are measured in degrees Celsius. An alarm is triggered once | |
| when the Overtemperature Shutdown limit is crossed; it is triggered again | |
| as soon as it drops below the Hysteresis value. A more useful behavior | |
| can be found by setting the Hysteresis value to +127 degrees Celsius; in | |
| this case, alarms are issued during all the time when the actual temperature | |
| is above the Overtemperature Shutdown value. Measurements are guaranteed | |
| between -55 and +125 degrees, with 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 4.08 volts, with a resolution | |
| of 0.016 volt. | |
| The VID lines encode the core voltage value: the voltage level your processor | |
| should work with. This is hardcoded by the mainboard and/or processor itself. | |
| It is a value in volts. When it is unconnected, you will often find the | |
| value 3.50 V here. | |
| 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 1.5 seconds since the last update). This means that you can easily | |
| miss once-only alarms. | |
| The LM7* only updates its values each 1.5 seconds; reading it more often | |
| will do no harm, but will return 'old' values. |