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