Documentation/hwmon/lm73

   1 Kernel driver lm73
   2 ==================
   3
   4 Supported chips:
   5
   6   * Texas Instruments LM73
   7
   8     Prefix: 'lm73'
   9
  10     Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e
  11
  12     Datasheet: Publicly available at the Texas Instruments website
  13
  14                http://www.ti.com/product/lm73
  15
  16
  17 Author: Guillaume Ligneul <guillaume.ligneul@gmail.com>
  18
  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
  39     ============= ============= ============
  40     Resolution    Conv. Time    Input Range
  41     (C/LSB)       (msec)        (msec)
  42     ============= ============= ============
  43     0.25          14             0..14
  44     0.125         28            15..28
  45     0.0625        56            29..56
  46     0.03125       112           57..infinity
  47     ============= ============= ============
  48
  49 The following examples show how the 'update_interval' attribute can be
  50 used to change the conversion time::
  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.
  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.