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-rw-r--r-- | Documentation/hwmon/ds1621 | 51 |
1 files changed, 3 insertions, 48 deletions
diff --git a/Documentation/hwmon/ds1621 b/Documentation/hwmon/ds1621 index 1fee6f1e6bc5..5e97f333c4df 100644 --- a/Documentation/hwmon/ds1621 +++ b/Documentation/hwmon/ds1621 | |||
@@ -49,12 +49,9 @@ of up to +/- 0.5 degrees even when compared against precise temperature | |||
49 | readings. Be sure to have a high vs. low temperature limit gap of al least | 49 | readings. Be sure to have a high vs. low temperature limit gap of al least |
50 | 1.0 degree Celsius to avoid Tout "bouncing", though! | 50 | 1.0 degree Celsius to avoid Tout "bouncing", though! |
51 | 51 | ||
52 | As for alarms, you can read the alarm status of the DS1621 via the 'alarms' | 52 | The alarm bits are set when the high or low limits are met or exceeded and |
53 | /sys file interface. The result consists mainly of bit 6 and 5 of the | 53 | are reset by the module as soon as the respective temperature ranges are |
54 | configuration register of the chip; bit 6 (0x40 or 64) is the high alarm | 54 | left. |
55 | bit and bit 5 (0x20 or 32) the low one. These bits are set when the high or | ||
56 | low limits are met or exceeded and are reset by the module as soon as the | ||
57 | respective temperature ranges are left. | ||
58 | 55 | ||
59 | The alarm registers are in no way suitable to find out about the actual | 56 | The alarm registers are in no way suitable to find out about the actual |
60 | status of Tout. They will only tell you about its history, whether or not | 57 | status of Tout. They will only tell you about its history, whether or not |
@@ -64,45 +61,3 @@ with neither of the alarms set. | |||
64 | 61 | ||
65 | Temperature conversion of the DS1621 takes up to 1000ms; internal access to | 62 | Temperature conversion of the DS1621 takes up to 1000ms; internal access to |
66 | non-volatile registers may last for 10ms or below. | 63 | non-volatile registers may last for 10ms or below. |
67 | |||
68 | High Accuracy Temperature Reading | ||
69 | --------------------------------- | ||
70 | |||
71 | As said before, the temperature issued via the 9-bit i2c-bus data is | ||
72 | somewhat arbitrary. Internally, the temperature conversion is of a | ||
73 | different kind that is explained (not so...) well in the DS1621 data sheet. | ||
74 | To cut the long story short: Inside the DS1621 there are two oscillators, | ||
75 | both of them biassed by a temperature coefficient. | ||
76 | |||
77 | Higher resolution of the temperature reading can be achieved using the | ||
78 | internal projection, which means taking account of REG_COUNT and REG_SLOPE | ||
79 | (the driver manages them): | ||
80 | |||
81 | Taken from Dallas Semiconductors App Note 068: 'Increasing Temperature | ||
82 | Resolution on the DS1620' and App Note 105: 'High Resolution Temperature | ||
83 | Measurement with Dallas Direct-to-Digital Temperature Sensors' | ||
84 | |||
85 | - Read the 9-bit temperature and strip the LSB (Truncate the .5 degs) | ||
86 | - The resulting value is TEMP_READ. | ||
87 | - Then, read REG_COUNT. | ||
88 | - And then, REG_SLOPE. | ||
89 | |||
90 | TEMP = TEMP_READ - 0.25 + ((REG_SLOPE - REG_COUNT) / REG_SLOPE) | ||
91 | |||
92 | Note that this is what the DONE bit in the DS1621 configuration register is | ||
93 | good for: Internally, one temperature conversion takes up to 1000ms. Before | ||
94 | that conversion is complete you will not be able to read valid things out | ||
95 | of REG_COUNT and REG_SLOPE. The DONE bit, as you may have guessed by now, | ||
96 | tells you whether the conversion is complete ("done", in plain English) and | ||
97 | thus, whether the values you read are good or not. | ||
98 | |||
99 | The DS1621 has two modes of operation: "Continuous" conversion, which can | ||
100 | be understood as the default stand-alone mode where the chip gets the | ||
101 | temperature and controls external devices via its Tout pin or tells other | ||
102 | i2c's about it if they care. The other mode is called "1SHOT", that means | ||
103 | that it only figures out about the temperature when it is explicitly told | ||
104 | to do so; this can be seen as power saving mode. | ||
105 | |||
106 | Now if you want to read REG_COUNT and REG_SLOPE, you have to either stop | ||
107 | the continuous conversions until the contents of these registers are valid, | ||
108 | or, in 1SHOT mode, you have to have one conversion made. | ||