blob: 74e909be6ef772b63b3ffb12b3f19d61378735c0 [file] [log] [blame]
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
Author: Guillaume Ligneul <>
Documentation: Chris Verges <>
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
$ cat temp1_input
$ echo 22 > update_interval
$ cat update_interval
$ cat temp1_input
$ echo 56 > update_interval
$ cat update_interval
$ cat temp1_input
$ echo 85 > update_interval
$ cat update_interval
$ cat temp1_input
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.