Kernel driver ds1621
  ====================
  
  Supported chips:
    * Dallas Semiconductor DS1621
      Prefix: 'ds1621'
      Addresses scanned: I2C 0x48 - 0x4f
      Datasheet: Publicly available at the Dallas Semiconductor website
                 http://www.dalsemi.com/
    * Dallas Semiconductor DS1625
      Prefix: 'ds1621'
      Addresses scanned: I2C 0x48 - 0x4f
      Datasheet: Publicly available at the Dallas Semiconductor website
                 http://www.dalsemi.com/
  
  Authors:
          Christian W. Zuckschwerdt <zany@triq.net>
          valuable contributions by Jan M. Sendler <sendler@sendler.de>
          ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
          with the help of Jean Delvare <khali@linux-fr.org>
  
  Module Parameters
  ------------------
  
  * polarity int
    Output's polarity: 0 = active high, 1 = active low
  
  Description
  -----------
  
  The DS1621 is a (one instance) digital thermometer and thermostat. It has
  both high and low temperature limits which can be user defined (i.e.
  programmed into non-volatile on-chip registers). Temperature range is -55
  degree Celsius to +125 in 0.5 increments. You may convert this into a
  Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
  parameter is not provided, original value is used.
  
  As for the thermostat, behavior can also be programmed using the polarity
  toggle. On the one hand ("heater"), the thermostat output of the chip,
  Tout, will trigger when the low limit temperature is met or underrun and
  stays high until the high limit is met or exceeded. On the other hand
  ("cooler"), vice versa. That way "heater" equals "active low", whereas
  "conditioner" equals "active high". Please note that the DS1621 data sheet
  is somewhat misleading in this point since setting the polarity bit does
  not simply invert Tout.
  
  A second thing is that, during extensive testing, Tout showed a tolerance
  of up to +/- 0.5 degrees even when compared against precise temperature
  readings. Be sure to have a high vs. low temperature limit gap of al least
  1.0 degree Celsius to avoid Tout "bouncing", though!

  The alarm bits are set when the high or low limits are met or exceeded and
  are reset by the module as soon as the respective temperature ranges are
  left.

  
  The alarm registers are in no way suitable to find out about the actual
  status of Tout. They will only tell you about its history, whether or not
  any of the limits have ever been met or exceeded since last power-up or
  reset. Be aware: When testing, it showed that the status of Tout can change
  with neither of the alarms set.
  
  Temperature conversion of the DS1621 takes up to 1000ms; internal access to
  non-volatile registers may last for 10ms or below.