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.