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+Kernel driver ds1621
+====================
+
+Supported chips:
+  * Dallas Semiconductor / Maxim Integrated DS1621
+    Prefix: 'ds1621'
+    Addresses scanned: none
+    Datasheet: Publicly available from www.maximintegrated.com
+
+  * Dallas Semiconductor DS1625
+    Prefix: 'ds1625'
+    Addresses scanned: none
+    Datasheet: Publicly available from www.datasheetarchive.com
+
+  * Maxim Integrated DS1631
+    Prefix: 'ds1631'
+    Addresses scanned: none
+    Datasheet: Publicly available from www.maximintegrated.com
+
+  * Maxim Integrated DS1721
+    Prefix: 'ds1721'
+    Addresses scanned: none
+    Datasheet: Publicly available from www.maximintegrated.com
+
+  * Maxim Integrated DS1731
+    Prefix: 'ds1731'
+    Addresses scanned: none
+    Datasheet: Publicly available from www.maximintegrated.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 <jdelvare@suse.de>
+
+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.
+
+Since there is no version or vendor identification register, there is
+no unique identification for these devices. Therefore, explicit device
+instantiation is required for correct device identification and functionality
+(one device per address in this address range: 0x48..0x4f).
+
+The DS1625 is pin compatible and functionally equivalent with the DS1621,
+but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are
+also pin compatible with the DS1621 and provide multi-resolution support.
+
+Additionally, the DS1721 data sheet says the temperature flags (THF and TLF)
+are used internally, however, these flags do get set and cleared as the actual
+temperature crosses the min or max settings (which by default are set to 75
+and 80 degrees respectively).
+
+Temperature Conversion:
+-----------------------
+DS1621 - 750ms (older devices may take up to 1000ms)
+DS1625 - 500ms
+DS1631 - 93ms..750ms for 9..12 bits resolution, respectively.
+DS1721 - 93ms..750ms for 9..12 bits resolution, respectively.
+DS1731 - 93ms..750ms for 9..12 bits resolution, respectively.
+
+Note:
+On the DS1621, internal access to non-volatile registers may last for 10ms
+or less (unverified on the other devices).
+
+Temperature Accuracy:
+---------------------
+DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees)
+DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees)
+DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees)
+DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees)
+DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees)
+
+Note:
+Please refer to the device datasheets for accuracy at other temperatures.
+
+Temperature Resolution:
+-----------------------
+As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution
+support, which is achieved via the R0 and R1 config register bits, where:
+
+R0..R1
+------
+ 0  0 => 9 bits, 0.5 degrees Celcius
+ 1  0 => 10 bits, 0.25 degrees Celcius
+ 0  1 => 11 bits, 0.125 degrees Celcius
+ 1  1 => 12 bits, 0.0625 degrees Celcius
+
+Note:
+At initial device power-on, the default resolution is set to 12-bits.
+
+The resolution mode for the DS1631, DS1721, or DS1731 can be changed from
+userspace, via the device 'update_interval' sysfs attribute. This attribute
+will normalize the range of input values to the device maximum resolution
+values defined in the datasheet as follows:
+
+Resolution    Conversion Time    Input Range
+ (C/LSB)       (msec)             (msec)
+------------------------------------------------
+0.5             93.75              0....94
+0.25            187.5              95...187
+0.125           375                188..375
+0.0625          750                376..infinity
+------------------------------------------------
+
+The following examples show how the 'update_interval' attribute can be
+used to change the conversion time:
+
+$ cat update_interval
+750
+$ cat temp1_input
+22062
+$
+$ echo 300 > update_interval
+$ cat update_interval
+375
+$ cat temp1_input
+22125
+$
+$ echo 150 > update_interval
+$ cat update_interval
+188
+$ cat temp1_input
+22250
+$
+$ echo 1 > update_interval
+$ cat update_interval
+94
+$ cat temp1_input
+22000
+$
+$ echo 1000 > update_interval
+$ cat update_interval
+750
+$ cat temp1_input
+22062
+$
+
+As shown, the ds1621 driver automatically adjusts the 'update_interval'
+user input, via a step function. Reading back the 'update_interval' value
+after a write operation provides the conversion time used by the device.
+
+Mathematically, the resolution can be derived from the conversion time
+via the following function:
+
+   g(x) = 0.5 * [minimum_conversion_time/x]
+
+where:
+ -> 'x' = the output from 'update_interval'
+ -> 'g(x)' = the resolution in degrees C per LSB.
+ -> 93.75ms = minimum conversion time