linux/Documentation/hwmon/pc87427
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   1Kernel driver pc87427
   2=====================
   3
   4Supported chips:
   5  * National Semiconductor PC87427
   6    Prefix: 'pc87427'
   7    Addresses scanned: none, address read from Super I/O config space
   8    Datasheet: No longer available
   9
  10Author: Jean Delvare <khali@linux-fr.org>
  11
  12Thanks to Amir Habibi at Candelis for setting up a test system, and to
  13Michael Kress for testing several iterations of this driver.
  14
  15
  16Description
  17-----------
  18
  19The National Semiconductor Super I/O chip includes complete hardware
  20monitoring capabilities. It can monitor up to 18 voltages, 8 fans and
  216 temperature sensors. Only the fans and temperatures are supported at
  22the moment, voltages aren't.
  23
  24This chip also has fan controlling features (up to 4 PWM outputs),
  25which are partly supported by this driver.
  26
  27The driver assumes that no more than one chip is present, which seems
  28reasonable.
  29
  30
  31Fan Monitoring
  32--------------
  33
  34Fan rotation speeds are reported as 14-bit values from a gated clock
  35signal. Speeds down to 83 RPM can be measured.
  36
  37An alarm is triggered if the rotation speed drops below a programmable
  38limit. Another alarm is triggered if the speed is too low to be measured
  39(including stalled or missing fan).
  40
  41
  42Fan Speed Control
  43-----------------
  44
  45Fan speed can be controlled by PWM outputs. There are 4 possible modes:
  46always off, always on, manual and automatic. The latter isn't supported
  47by the driver: you can only return to that mode if it was the original
  48setting, and the configuration interface is missing.
  49
  50
  51Temperature Monitoring
  52----------------------
  53
  54The PC87427 relies on external sensors (following the SensorPath
  55standard), so the resolution and range depend on the type of sensor
  56connected. The integer part can be 8-bit or 9-bit, and can be signed or
  57not. I couldn't find a way to figure out the external sensor data
  58temperature format, so user-space adjustment (typically by a factor 2)
  59may be required.
  60
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