Kernel driver lm90
==================

Supported chips:
  * National Semiconductor LM90
    Prefix: 'lm90'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/pf/LM/LM90.html
  * National Semiconductor LM89
    Prefix: 'lm99'
    Addresses scanned: I2C 0x4c and 0x4d
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/pf/LM/LM89.html
  * National Semiconductor LM99
    Prefix: 'lm99'
    Addresses scanned: I2C 0x4c and 0x4d
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/pf/LM/LM99.html
  * National Semiconductor LM86
    Prefix: 'lm86'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the National Semiconductor website
               http://www.national.com/pf/LM/LM86.html
  * Analog Devices ADM1032
    Prefix: 'adm1032'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the Analog Devices website
               http://products.analog.com/products/info.asp?product=ADM1032
  * Analog Devices ADT7461
    Prefix: 'adt7461'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the Analog Devices website
               http://products.analog.com/products/info.asp?product=ADT7461
    Note: Only if in ADM1032 compatibility mode
  * Maxim MAX6657
    Prefix: 'max6657'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the Maxim website
               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  * Maxim MAX6658
    Prefix: 'max6657'
    Addresses scanned: I2C 0x4c
    Datasheet: Publicly available at the Maxim website
               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
  * Maxim MAX6659
    Prefix: 'max6657'
    Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e)
    Datasheet: Publicly available at the Maxim website
               http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578


Author: Jean Delvare <khali@linux-fr.org>


Description
-----------

The LM90 is a digital temperature sensor. It senses its own temperature as
well as the temperature of up to one external diode. It is compatible
with many other devices such as the LM86, the LM89, the LM99, the ADM1032,
the MAX6657, MAX6658 and the MAX6659 all of which are supported by this driver.
Note that there is no easy way to differentiate between the last three
variants. The extra address and features of the MAX6659 are not supported by
this driver. Additionally, the ADT7461 is supported if found in ADM1032
compatibility mode.

The specificity of this family of chipsets over the ADM1021/LM84
family is that it features critical limits with hysteresis, and an
increased resolution of the remote temperature measurement.

The different chipsets of the family are not strictly identical, although
very similar. This driver doesn't handle any specific feature for now,
but could if there ever was a need for it. For reference, here comes a
non-exhaustive list of specific features:

LM90:
  * Filter and alert configuration register at 0xBF.
  * ALERT is triggered by temperatures over critical limits.

LM86 and LM89:
  * Same as LM90
  * Better external channel accuracy

LM99:
  * Same as LM89
  * External temperature shifted by 16 degrees down

ADM1032:
  * Consecutive alert register at 0x22.
  * Conversion averaging.
  * Up to 64 conversions/s.
  * ALERT is triggered by open remote sensor.

ADT7461
  * Extended temperature range (breaks compatibility)
  * Lower resolution for remote temperature

MAX6657 and MAX6658:
  * Remote sensor type selection

MAX6659
  * Selectable address
  * Second critical temperature limit
  * Remote sensor type selection

All temperature values are given in degrees Celsius. Resolution
is 1.0 degree for the local temperature, 0.125 degree for the remote
temperature.

Each sensor has its own high and low limits, plus a critical limit.
Additionally, there is a relative hysteresis value common to both critical
values. To make life easier to user-space applications, two absolute values
are exported, one for each channel, but these values are of course linked.
Only the local hysteresis can be set from user-space, and the same delta
applies to the remote hysteresis.

The lm90 driver will not update its values more frequently than every
other second; reading them more often will do no harm, but will return
'old' values.