]>
Commit | Line | Data |
---|---|---|
8c14d126 CV |
1 | Kernel driver lm73 |
2 | ================== | |
3 | ||
4 | Supported chips: | |
5 | * Texas Instruments LM73 | |
6 | Prefix: 'lm73' | |
7 | Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e | |
8 | Datasheet: Publicly available at the Texas Instruments website | |
9 | http://www.ti.com/product/lm73 | |
10 | ||
11 | Author: Guillaume Ligneul <guillaume.ligneul@gmail.com> | |
12 | Documentation: Chris Verges <kg4ysn@gmail.com> | |
13 | ||
14 | ||
15 | Description | |
16 | ----------- | |
17 | ||
18 | The LM73 is a digital temperature sensor. All temperature values are | |
19 | given in degrees Celsius. | |
20 | ||
21 | Measurement Resolution Support | |
22 | ------------------------------ | |
23 | ||
24 | The LM73 supports four resolutions, defined in terms of degrees C per | |
25 | LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode | |
26 | affects the conversion time of the LM73's analog-to-digital converter. | |
27 | From userspace, the desired resolution can be specified as a function of | |
28 | conversion time via the 'update_interval' sysfs attribute for the | |
29 | device. This attribute will normalize ranges of input values to the | |
30 | maximum times defined for the resolution in the datasheet. | |
31 | ||
32 | Resolution Conv. Time Input Range | |
33 | (C/LSB) (msec) (msec) | |
34 | -------------------------------------- | |
35 | 0.25 14 0..14 | |
36 | 0.125 28 15..28 | |
37 | 0.0625 56 29..56 | |
38 | 0.03125 112 57..infinity | |
39 | -------------------------------------- | |
40 | ||
41 | The following examples show how the 'update_interval' attribute can be | |
42 | used to change the conversion time: | |
43 | ||
44 | $ echo 0 > update_interval | |
45 | $ cat update_interval | |
46 | 14 | |
47 | $ cat temp1_input | |
48 | 24250 | |
49 | ||
50 | $ echo 22 > update_interval | |
51 | $ cat update_interval | |
52 | 28 | |
53 | $ cat temp1_input | |
54 | 24125 | |
55 | ||
56 | $ echo 56 > update_interval | |
57 | $ cat update_interval | |
58 | 56 | |
59 | $ cat temp1_input | |
60 | 24062 | |
61 | ||
62 | $ echo 85 > update_interval | |
63 | $ cat update_interval | |
64 | 112 | |
65 | $ cat temp1_input | |
66 | 24031 | |
67 | ||
68 | As shown here, the lm73 driver automatically adjusts any user input for | |
69 | 'update_interval' via a step function. Reading back the | |
70 | 'update_interval' value after a write operation will confirm the | |
71 | conversion time actively in use. | |
72 | ||
73 | Mathematically, the resolution can be derived from the conversion time | |
74 | via the following function: | |
75 | ||
76 | g(x) = 0.250 * [log(x/14) / log(2)] | |
77 | ||
78 | where 'x' is the output from 'update_interval' and 'g(x)' is the | |
79 | resolution in degrees C per LSB. | |
2bf9233a CV |
80 | |
81 | Alarm Support | |
82 | ------------- | |
83 | ||
84 | The LM73 features a simple over-temperature alarm mechanism. This | |
85 | feature is exposed via the sysfs attributes. | |
86 | ||
87 | The attributes 'temp1_max_alarm' and 'temp1_min_alarm' are flags | |
88 | provided by the LM73 that indicate whether the measured temperature has | |
89 | passed the 'temp1_max' and 'temp1_min' thresholds, respectively. These | |
90 | values _must_ be read to clear the registers on the LM73. |