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diff --git a/Documentation/i2c/chips/lm78 b/Documentation/i2c/chips/lm78 new file mode 100644 index 00000000000..357086ed7f6 --- /dev/null +++ b/Documentation/i2c/chips/lm78 @@ -0,0 +1,82 @@ +Kernel driver lm78 +================== + +Supported chips: + * National Semiconductor LM78 + Prefix: 'lm78' + Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports) + Datasheet: Publicly available at the National Semiconductor website + http://www.national.com/ + * National Semiconductor LM78-J + Prefix: 'lm78-j' + Addresses scanned: I2C 0x20 - 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 0x20 - 0x2f, ISA 0x290 (8 I/O ports) + Datasheet: Publicly available at the National Semiconductor website + http://www.national.com/ + +Author: Frodo Looijaard <frodol@dds.nl> + +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. + +In addition to the alarms described above, there are a couple of additional +ones. There is a BTI alarm, which gets triggered when an external chip has +crossed its limits. Usually, this is connected to all LM75 chips; if at +least one crosses its limits, this bit gets set. The CHAS alarm triggers +if your computer case is open. The FIFO alarms should never trigger; it +indicates an internal error. The SMI_IN alarm indicates some other chip +has triggered an SMI interrupt. As we do not use SMI interrupts at all, +this condition usually indicates there is a problem with some other +device. + +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. |