forked from Minki/linux
ed7c34e89d
Due to a lack of device and vendor identification registers, the Dallas/Maxim DS16xx devices cannot be uniquely detected, sometimes resulting in false positives. Therefore, the detect function is being removed in favor of explicit device instantiation. Signed-off-by: Robert Coulson <rob.coulson@gmail.com> Acked-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
163 lines
5.8 KiB
Plaintext
163 lines
5.8 KiB
Plaintext
Kernel driver ds1621
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====================
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Supported chips:
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* Dallas Semiconductor / Maxim Integrated DS1621
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Prefix: 'ds1621'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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* Dallas Semiconductor DS1625
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Prefix: 'ds1625'
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Addresses scanned: none
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Datasheet: Publicly available from www.datasheetarchive.com
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* Maxim Integrated DS1631
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Prefix: 'ds1631'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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* Maxim Integrated DS1721
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Prefix: 'ds1721'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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Authors:
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Christian W. Zuckschwerdt <zany@triq.net>
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valuable contributions by Jan M. Sendler <sendler@sendler.de>
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ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
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with the help of Jean Delvare <khali@linux-fr.org>
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Module Parameters
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------------------
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* polarity int
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Output's polarity: 0 = active high, 1 = active low
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Description
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-----------
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The DS1621 is a (one instance) digital thermometer and thermostat. It has
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both high and low temperature limits which can be user defined (i.e.
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programmed into non-volatile on-chip registers). Temperature range is -55
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degree Celsius to +125 in 0.5 increments. You may convert this into a
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Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
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parameter is not provided, original value is used.
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As for the thermostat, behavior can also be programmed using the polarity
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toggle. On the one hand ("heater"), the thermostat output of the chip,
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Tout, will trigger when the low limit temperature is met or underrun and
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stays high until the high limit is met or exceeded. On the other hand
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("cooler"), vice versa. That way "heater" equals "active low", whereas
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"conditioner" equals "active high". Please note that the DS1621 data sheet
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is somewhat misleading in this point since setting the polarity bit does
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not simply invert Tout.
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A second thing is that, during extensive testing, Tout showed a tolerance
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of up to +/- 0.5 degrees even when compared against precise temperature
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readings. Be sure to have a high vs. low temperature limit gap of al least
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1.0 degree Celsius to avoid Tout "bouncing", though!
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The alarm bits are set when the high or low limits are met or exceeded and
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are reset by the module as soon as the respective temperature ranges are
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left.
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The alarm registers are in no way suitable to find out about the actual
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status of Tout. They will only tell you about its history, whether or not
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any of the limits have ever been met or exceeded since last power-up or
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reset. Be aware: When testing, it showed that the status of Tout can change
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with neither of the alarms set.
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Temperature conversion of the DS1621 takes up to 1000ms; internal access to
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non-volatile registers may last for 10ms or below.
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The DS1625 is pin compatible and functionally equivalent with the DS1621,
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but the DS1621 is meant to replace it. The DS1631 and DS1721 are also
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pin compatible with the DS1621, but provide multi-resolution support.
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Since there is no version or vendor identification register, there is
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no unique identification for these devices. Therefore, explicit device
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instantiation is required for correct device identification and functionality.
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And, for correct identification and operation, each device must be
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explicitly instantiated, one device per address, in this address
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range: 0x48..0x4f.
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The DS1721 is pin compatible with the DS1621, has an accuracy of +/- 1.0
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degree Celsius over a -10 to +85 degree range, a minimum/maximum alarm
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default setting of 75 and 80 degrees respectively, and a maximum conversion
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time of 750ms.
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In addition, the DS1721 supports four resolution settings from 9 to 12 bits
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(defined in degrees C per LSB: 0.5, 0.25, 0.125, and 0.0625, respectifully),
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that are set at device power on to the highest resolution: 12-bits.
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One additional note about the ds1721 is that although the data sheet says
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the temperature flags (THF and TLF) are used internally, these flags do
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get set and cleared as the actual temperature crosses the min or max settings.
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The DS1631 is also pin compatible with the DS1621 and feature compatible with
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the DS1721, however the DS1631 accuracy is +/- 0.5 degree Celsius over the
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same range.
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Changing the DS1631/1721 resolution mode affects the conversion time and can be
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done from userspace, via the device 'update_interval' sysfs attribute. This
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attribute will normalize range of input values to the device maximum resolution
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values defined in the datasheet as such:
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Resolution Conversion Time Input Range
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(C/LSB) (msec) (msec)
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--------------------------------------------
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0.5 93.75 0....94
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0.25 187.5 95...187
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0.125 375 188..375
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0.0625 750 376..infinity
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--------------------------------------
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The following examples show how the 'update_interval' attribute can be
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used to change the conversion time:
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$ cat update_interval
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750
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$ cat temp1_input
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22062
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$
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$ echo 300 > update_interval
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$ cat update_interval
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375
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$ cat temp1_input
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22125
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$
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$ echo 150 > update_interval
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$ cat update_interval
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188
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$ cat temp1_input
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22250
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$
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$ echo 1 > update_interval
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$ cat update_interval
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94
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$ cat temp1_input
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22000
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$
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$ echo 1000 > update_interval
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$ cat update_interval
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750
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$ cat temp1_input
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22062
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$
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As shown, the ds1621 driver automatically adjusts the 'update_interval'
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user input, via a step function. Reading back the 'update_interval' value
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after a write operation provides the conversion time used by the device.
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Mathematically, the resolution can be derived from the conversion time
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via the following function:
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g(x) = 0.5 * [minimum_conversion_time/x]
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where:
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-> 'x' = the output from 'update_interval'
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-> 'g(x)' = the resolution in degrees C per LSB.
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-> 93.75ms = minimum conversion time
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