projects / linux-2.6-block.git / blame
| Commit | Line | Data |
|---|---|---|
| 8c14d126 CV |
1 | Kernel driver lm73 |
| 2 | ================== | |
| 3 | ||
| 4 | Supported chips: | |
| b04f2f7d | 5 | |
| 8c14d126 | 6 | * Texas Instruments LM73 |
| b04f2f7d | 7 | |
| 8c14d126 | 8 | Prefix: 'lm73' |
| b04f2f7d | 9 | |
| 8c14d126 | 10 | Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e |
| b04f2f7d | 11 | |
| 8c14d126 | 12 | Datasheet: Publicly available at the Texas Instruments website |
| b04f2f7d MCC |
13 | |
| 14 | http://www.ti.com/product/lm73 | |
| 15 | ||
| 8c14d126 CV |
16 | |
| 17 | Author: Guillaume Ligneul <guillaume.ligneul@gmail.com> | |
| b04f2f7d | 18 | |
| 8c14d126 CV |
19 | Documentation: Chris Verges <kg4ysn@gmail.com> |
| 20 | ||
| 21 | ||
| 22 | Description | |
| 23 | ----------- | |
| 24 | ||
| 25 | The LM73 is a digital temperature sensor. All temperature values are | |
| 26 | given in degrees Celsius. | |
| 27 | ||
| 28 | Measurement Resolution Support | |
| 29 | ------------------------------ | |
| 30 | ||
| 31 | The LM73 supports four resolutions, defined in terms of degrees C per | |
| 32 | LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode | |
| 33 | affects the conversion time of the LM73's analog-to-digital converter. | |
| 34 | From userspace, the desired resolution can be specified as a function of | |
| 35 | conversion time via the 'update_interval' sysfs attribute for the | |
| 36 | device. This attribute will normalize ranges of input values to the | |
| 37 | maximum times defined for the resolution in the datasheet. | |
| 38 | ||
| b04f2f7d | 39 | ============= ============= ============ |
| 8c14d126 CV |
40 | Resolution Conv. Time Input Range |
| 41 | (C/LSB) (msec) (msec) | |
| b04f2f7d | 42 | ============= ============= ============ |
| 8c14d126 CV |
43 | 0.25 14 0..14 |
| 44 | 0.125 28 15..28 | |
| 45 | 0.0625 56 29..56 | |
| 46 | 0.03125 112 57..infinity | |
| b04f2f7d | 47 | ============= ============= ============ |
| 8c14d126 CV |
48 | |
| 49 | The following examples show how the 'update_interval' attribute can be | |
| b04f2f7d | 50 | used to change the conversion time:: |
| 8c14d126 CV |
51 | |
| 52 | $ echo 0 > update_interval | |
| 53 | $ cat update_interval | |
| 54 | 14 | |
| 55 | $ cat temp1_input | |
| 56 | 24250 | |
| 57 | ||
| 58 | $ echo 22 > update_interval | |
| 59 | $ cat update_interval | |
| 60 | 28 | |
| 61 | $ cat temp1_input | |
| 62 | 24125 | |
| 63 | ||
| 64 | $ echo 56 > update_interval | |
| 65 | $ cat update_interval | |
| 66 | 56 | |
| 67 | $ cat temp1_input | |
| 68 | 24062 | |
| 69 | ||
| 70 | $ echo 85 > update_interval | |
| 71 | $ cat update_interval | |
| 72 | 112 | |
| 73 | $ cat temp1_input | |
| 74 | 24031 | |
| 75 | ||
| 76 | As shown here, the lm73 driver automatically adjusts any user input for | |
| 77 | 'update_interval' via a step function. Reading back the | |
| 78 | 'update_interval' value after a write operation will confirm the | |
| 79 | conversion time actively in use. | |
| 80 | ||
| 81 | Mathematically, the resolution can be derived from the conversion time | |
| 82 | via the following function: | |
| 83 | ||
| 84 | g(x) = 0.250 * [log(x/14) / log(2)] | |
| 85 | ||
| 86 | where 'x' is the output from 'update_interval' and 'g(x)' is the | |
| 87 | resolution in degrees C per LSB. | |
| 2bf9233a CV |
88 | |
| 89 | Alarm Support | |
| 90 | ------------- | |
| 91 | ||
| 92 | The LM73 features a simple over-temperature alarm mechanism. This | |
| 93 | feature is exposed via the sysfs attributes. | |
| 94 | ||
| 95 | The attributes 'temp1_max_alarm' and 'temp1_min_alarm' are flags | |
| 96 | provided by the LM73 that indicate whether the measured temperature has | |
| 97 | passed the 'temp1_max' and 'temp1_min' thresholds, respectively. These | |
| 98 | values _must_ be read to clear the registers on the LM73. |