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- 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.
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