91 lines
2.7 KiB
Plaintext
91 lines
2.7 KiB
Plaintext
|
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.
|