177 lines
7.0 KiB
Plaintext
177 lines
7.0 KiB
Plaintext
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 and 0x4d
|
|
Datasheet: Publicly available at the Analog Devices website
|
|
http://www.analog.com/en/prod/0,2877,ADM1032,00.html
|
|
* Analog Devices ADT7461
|
|
Prefix: 'adt7461'
|
|
Addresses scanned: I2C 0x4c and 0x4d
|
|
Datasheet: Publicly available at the Analog Devices website
|
|
http://www.analog.com/en/prod/0,2877,ADT7461,00.html
|
|
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
|
|
* Maxim MAX6680
|
|
Prefix: 'max6680'
|
|
Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
|
|
0x4c, 0x4d and 0x4e
|
|
Datasheet: Publicly available at the Maxim website
|
|
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
|
|
* Maxim MAX6681
|
|
Prefix: 'max6680'
|
|
Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
|
|
0x4c, 0x4d and 0x4e
|
|
Datasheet: Publicly available at the Maxim website
|
|
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
|
|
|
|
|
|
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, MAX6659, MAX6680 and the MAX6681 all of which are
|
|
supported by this driver.
|
|
|
|
Note that there is no easy way to differentiate between the MAX6657,
|
|
MAX6658 and MAX6659 variants. The extra address and features of the
|
|
MAX6659 are not supported by this driver. The MAX6680 and MAX6681 only
|
|
differ in their pinout, therefore they obviously can't (and don't need to)
|
|
be distinguished. 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 selection
|
|
|
|
MAX6659:
|
|
* Selectable address
|
|
* Second critical temperature limit
|
|
* Remote sensor type selection
|
|
|
|
MAX6680 and MAX6681:
|
|
* Selectable address
|
|
* 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.
|
|
|
|
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 explicitly 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
|
|
sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
|
|
to that file to enable PEC again.
|