http://www.national.com/pf/LM/LM86.html
* Analog Devices ADM1032
Prefix: 'adm1032'
- Addresses scanned: I2C 0x4c
+ Addresses scanned: I2C 0x4c and 0x4d
Datasheet: Publicly available at the Analog Devices website
- http://products.analog.com/products/info.asp?product=ADM1032
+ http://www.analog.com/en/prod/0,2877,ADM1032,00.html
* Analog Devices ADT7461
Prefix: 'adt7461'
- Addresses scanned: I2C 0x4c
+ Addresses scanned: I2C 0x4c and 0x4d
Datasheet: Publicly available at the Analog Devices website
- http://products.analog.com/products/info.asp?product=ADT7461
+ 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, 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>
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 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
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:
+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.
* 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
+ADT7461:
* Extended temperature range (breaks compatibility)
* Lower resolution for remote temperature
MAX6657 and MAX6658:
* Remote sensor type selection
-MAX6659
+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.
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.
git.samba.org / sfrench / cifs-2.6.git / blobdiff