| 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. |