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Diffstat (limited to 'kernel/Documentation/hwmon/ds1621')
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diff --git a/kernel/Documentation/hwmon/ds1621 b/kernel/Documentation/hwmon/ds1621 new file mode 100644 index 000000000..f775e612f --- /dev/null +++ b/kernel/Documentation/hwmon/ds1621 @@ -0,0 +1,187 @@ +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 |