root/lm-sensors/trunk/doc/chips/lm90 @ 3181

Kernel driver `lm90.o'
======================

Status: Complete and well tested

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 and 0x4d
    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 and 0x4d
    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 and 0x4d
    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>

License: GPL


Module Parameters
-----------------

* force: short array (min = 1, max = 48)
  List of adapter,address pairs to boldly assume to be present
* force_lm90: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `lm90' chip
* force_adm1032: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `adm1032' chip
* force_lm99: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `lm99' chip
* force_lm86: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `lm86' chip
* force_max6657: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `max6657' chip
* force_adt7461: short array (min = 1, max = 48)
  List of adapter,address pairs which are unquestionably assumed to contain
  a `adt7461' chip
* probe: short array (min = 1, max = 48)
  List of adapter,address pairs to scan additionally
* probe_range: short array (min = 1, max = 48)
  List of adapter,start-addr,end-addr triples to scan additionally
* ignore: short array (min = 1, max = 48)
  List of adapter,address pairs not to scan
* ignore_range: short array (min = 1, max = 48)
  List of adapter,start-addr,end-addr triples not to scan


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, the MAX6658, and the MAX6659, all of which are 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,
with the exception of SMBus PEC. 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.
  * SMBus PEC support for Write Byte and Receive Byte transactions.

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

MAX6657 and MAX6658:
  * Remote sensor type selecion

MAX6659
  * Selectable address
  * Second critical temperature limit

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.


PEC Support
-----------

The ADM1032 is the only chip of the family which supports PEC. It does
not support PEC on all transactions though, so some care must be taken.

When reading a register value, the PEC byte is computed and sent by the
ADM1032 chip. However, in the case of a combined transaction (SMBus Read
Byte), the ADM1032 computes the CRC value over only the second half of
the message rather than its entirety, because it thinks the first half
of the message belongs to a different transaction. As a result, the CRC
value differs from what the SMBus master expects, and all reads fail.

For this reason, the lm90 driver will enable PEC for the ADM1032 only if
the bus supports the SMBus Send Byte and Receive Byte transaction types.
These transactions will be used to read register values, instead of
SMBus Read Byte, and PEC will work properly.

Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
Instead, it will try to write the PEC value to the register (because the
SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
without PEC), which is not what we want. Thus, PEC is explicitely disabled
on SMBus Send Byte transactions in the lm90 driver.

PEC on byte data transactions represents a significant increase in bandwidth
usage (+33% for writes, +25% for reads) in normal conditions. With the need
to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
two transactions will typically mean twice as much delay waiting for
transaction completion, effectively doubling the register cache refresh time.
I guess reliability comes at a price, but it's quite expensive this time.

So, as not everyone might enjoy the slowdown, PEC can be disabled through
procfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
to that file to enable PEC again.


Chip Features
-------------

Chips 'lm90', adm1032', 'lm99', 'lm86', 'max6657' and 'adt7461'

LABEL                 LABEL CLASS           COMPUTE CLASS          MODE  MAGN
temp1                 -                     -                       R-     0
temp1_high            temp1                 temp1                   RW     0
temp1_low             temp1                 temp1                   RW     0
temp2                 -                     -                       R-     1
temp2_high            temp2                 temp2                   RW     1
temp2_low             temp2                 temp2                   RW     1
tcrit1                temp1                 temp1                   RW     0
tcrit2                temp2                 temp2                   RW     0
hyst1                 temp1                 temp1                   RW     0
hyst2                 temp2                 temp2                   R-     0
alarms                -                     -                       R-     0

LABEL                 FEATURE SYMBOL                              SYSCTL FILE:N
temp1                 SENSORS_LM90_LOCAL_TEMP                           temp1:3
temp1_high            SENSORS_LM90_LOCAL_HIGH                           temp1:1
temp1_low             SENSORS_LM90_LOCAL_LOW                            temp1:2
temp2                 SENSORS_LM90_REMOTE_TEMP                          temp2:3
temp2_high            SENSORS_LM90_REMOTE_HIGH                          temp2:1
temp2_low             SENSORS_LM90_REMOTE_LOW                           temp2:2
tcrit1                SENSORS_LM90_LOCAL_TCRIT                         tcrit1:1
tcrit2                SENSORS_LM90_REMOTE_TCRIT                        tcrit2:1
hyst1                 SENSORS_LM90_LOCAL_TCRIT_HYST                     hyst1:1
hyst2                 SENSORS_LM90_REMOTE_TCRIT_HYST                    hyst2:1
alarms                SENSORS_LM90_ALARMS                              alarms:1