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Diffstat (limited to 'kernel/Documentation/hwmon/lm73')
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diff --git a/kernel/Documentation/hwmon/lm73 b/kernel/Documentation/hwmon/lm73 new file mode 100644 index 000000000..8af059dcb --- /dev/null +++ b/kernel/Documentation/hwmon/lm73 @@ -0,0 +1,90 @@ +Kernel driver lm73 +================== + +Supported chips: + * Texas Instruments LM73 + Prefix: 'lm73' + Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e + Datasheet: Publicly available at the Texas Instruments website + http://www.ti.com/product/lm73 + +Author: Guillaume Ligneul <guillaume.ligneul@gmail.com> +Documentation: Chris Verges <kg4ysn@gmail.com> + + +Description +----------- + +The LM73 is a digital temperature sensor. All temperature values are +given in degrees Celsius. + +Measurement Resolution Support +------------------------------ + +The LM73 supports four resolutions, defined in terms of degrees C per +LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode +affects the conversion time of the LM73's analog-to-digital converter. +From userspace, the desired resolution can be specified as a function of +conversion time via the 'update_interval' sysfs attribute for the +device. This attribute will normalize ranges of input values to the +maximum times defined for the resolution in the datasheet. + + Resolution Conv. Time Input Range + (C/LSB) (msec) (msec) + -------------------------------------- + 0.25 14 0..14 + 0.125 28 15..28 + 0.0625 56 29..56 + 0.03125 112 57..infinity + -------------------------------------- + +The following examples show how the 'update_interval' attribute can be +used to change the conversion time: + + $ echo 0 > update_interval + $ cat update_interval + 14 + $ cat temp1_input + 24250 + + $ echo 22 > update_interval + $ cat update_interval + 28 + $ cat temp1_input + 24125 + + $ echo 56 > update_interval + $ cat update_interval + 56 + $ cat temp1_input + 24062 + + $ echo 85 > update_interval + $ cat update_interval + 112 + $ cat temp1_input + 24031 + +As shown here, the lm73 driver automatically adjusts any user input for +'update_interval' via a step function. Reading back the +'update_interval' value after a write operation will confirm the +conversion time actively in use. + +Mathematically, the resolution can be derived from the conversion time +via the following function: + + g(x) = 0.250 * [log(x/14) / log(2)] + +where 'x' is the output from 'update_interval' and 'g(x)' is the +resolution in degrees C per LSB. + +Alarm Support +------------- + +The LM73 features a simple over-temperature alarm mechanism. This +feature is exposed via the sysfs attributes. + +The attributes 'temp1_max_alarm' and 'temp1_min_alarm' are flags +provided by the LM73 that indicate whether the measured temperature has +passed the 'temp1_max' and 'temp1_min' thresholds, respectively. These +values _must_ be read to clear the registers on the LM73. |