78 lines
3.7 KiB
Plaintext
78 lines
3.7 KiB
Plaintext
Kernel driver lm78
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==================
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Supported chips:
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* National Semiconductor LM78 / LM78-J
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Prefix: 'lm78'
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Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/
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* National Semiconductor LM79
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Prefix: 'lm79'
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Addresses scanned: I2C 0x20 - 0x2f, ISA 0x290 (8 I/O ports)
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/
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Author: Frodo Looijaard <frodol@dds.nl>
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Description
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-----------
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This driver implements support for the National Semiconductor LM78, LM78-J
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and LM79. They are described as 'Microprocessor System Hardware Monitors'.
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There is almost no difference between the three supported chips. Functionally,
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the LM78 and LM78-J are exactly identical. The LM79 has one more VID line,
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which is used to report the lower voltages newer Pentium processors use.
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From here on, LM7* means either of these three types.
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The LM7* implements one temperature sensor, three fan rotation speed sensors,
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seven voltage sensors, VID lines, alarms, and some miscellaneous stuff.
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Temperatures are measured in degrees Celsius. An alarm is triggered once
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when the Overtemperature Shutdown limit is crossed; it is triggered again
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as soon as it drops below the Hysteresis value. A more useful behavior
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can be found by setting the Hysteresis value to +127 degrees Celsius; in
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this case, alarms are issued during all the time when the actual temperature
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is above the Overtemperature Shutdown value. Measurements are guaranteed
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between -55 and +125 degrees, with a resolution of 1 degree.
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Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
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triggered if the rotation speed has dropped below a programmable limit. Fan
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readings can be divided by a programmable divider (1, 2, 4 or 8) to give
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the readings more range or accuracy. Not all RPM values can accurately be
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represented, so some rounding is done. With a divider of 2, the lowest
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representable value is around 2600 RPM.
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Voltage sensors (also known as IN sensors) report their values in volts.
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An alarm is triggered if the voltage has crossed a programmable minimum
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or maximum limit. Note that minimum in this case always means 'closest to
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zero'; this is important for negative voltage measurements. All voltage
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inputs can measure voltages between 0 and 4.08 volts, with a resolution
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of 0.016 volt.
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The VID lines encode the core voltage value: the voltage level your processor
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should work with. This is hardcoded by the mainboard and/or processor itself.
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It is a value in volts. When it is unconnected, you will often find the
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value 3.50 V here.
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In addition to the alarms described above, there are a couple of additional
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ones. There is a BTI alarm, which gets triggered when an external chip has
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crossed its limits. Usually, this is connected to all LM75 chips; if at
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least one crosses its limits, this bit gets set. The CHAS alarm triggers
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if your computer case is open. The FIFO alarms should never trigger; it
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indicates an internal error. The SMI_IN alarm indicates some other chip
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has triggered an SMI interrupt. As we do not use SMI interrupts at all,
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this condition usually indicates there is a problem with some other
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device.
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If an alarm triggers, it will remain triggered until the hardware register
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is read at least once. This means that the cause for the alarm may
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already have disappeared! Note that in the current implementation, all
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hardware registers are read whenever any data is read (unless it is less
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than 1.5 seconds since the last update). This means that you can easily
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miss once-only alarms.
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The LM7* only updates its values each 1.5 seconds; reading it more often
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will do no harm, but will return 'old' values.
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