diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2009-03-30 17:54:32 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-03-30 17:54:32 -0700 |
commit | 3c6fae67d026d57f64eb3da9c0d0e76983e39ae3 (patch) | |
tree | a11f2ff6d99b382fff02a643f6b6b204efb9c40e /Documentation/hwmon/ds1621 | |
parent | c4e1aa67ed9e4e542a064bc271ddbf152b677e91 (diff) | |
parent | de15f093e666ccd542f6f7a0e3e917166a07ab44 (diff) |
Merge branch 'hwmon-for-linus' of git://jdelvare.pck.nerim.net/jdelvare-2.6
* 'hwmon-for-linus' of git://jdelvare.pck.nerim.net/jdelvare-2.6:
hwmon: (fschmd) Add support for the FSC Hades IC
hwmon: (fschmd) Add support for the FSC Syleus IC
i2c-i801: Instantiate FSC hardware montioring chips
dmi: Let dmi_walk() users pass private data
hwmon: Define a standard interface for chassis intrusion detection
Move the pcf8591 driver to hwmon
hwmon: (w83627ehf) Only expose in6 or temp3 on the W83667HG
hwmon: (w83627ehf) Add support for W83667HG
hwmon: (w83627ehf) Invert fan pin variables logic
hwmon: (hdaps) Fix Thinkpad X41 axis inversion
hwmon: (hdaps) Allow inversion of separate axis
hwmon: (ds1621) Clean up documentation
hwmon: (ds1621) Avoid unneeded register access
hwmon: (ds1621) Clean up register access
hwmon: (ds1621) Reorder code statements
Diffstat (limited to 'Documentation/hwmon/ds1621')
-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 1fee6f1e6bc..5e97f333c4d 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 readings. Be sure to have a high vs. low temperature limit gap of al least 1.0 degree Celsius to avoid Tout "bouncing", though! -As for alarms, you can read the alarm status of the DS1621 via the 'alarms' -/sys file interface. The result consists mainly of bit 6 and 5 of the -configuration register of the chip; bit 6 (0x40 or 64) is the high alarm -bit and bit 5 (0x20 or 32) the low one. These bits are set when the high or -low limits are met or exceeded and are reset by the module as soon as the -respective temperature ranges are left. +The alarm bits are set when the high or low limits are met or exceeded and +are reset by the module as soon as the respective temperature ranges are +left. The alarm registers are in no way suitable to find out about the actual status of Tout. They will only tell you about its history, whether or not @@ -64,45 +61,3 @@ with neither of the alarms set. Temperature conversion of the DS1621 takes up to 1000ms; internal access to non-volatile registers may last for 10ms or below. - -High Accuracy Temperature Reading ---------------------------------- - -As said before, the temperature issued via the 9-bit i2c-bus data is -somewhat arbitrary. Internally, the temperature conversion is of a -different kind that is explained (not so...) well in the DS1621 data sheet. -To cut the long story short: Inside the DS1621 there are two oscillators, -both of them biassed by a temperature coefficient. - -Higher resolution of the temperature reading can be achieved using the -internal projection, which means taking account of REG_COUNT and REG_SLOPE -(the driver manages them): - -Taken from Dallas Semiconductors App Note 068: 'Increasing Temperature -Resolution on the DS1620' and App Note 105: 'High Resolution Temperature -Measurement with Dallas Direct-to-Digital Temperature Sensors' - -- Read the 9-bit temperature and strip the LSB (Truncate the .5 degs) -- The resulting value is TEMP_READ. -- Then, read REG_COUNT. -- And then, REG_SLOPE. - - TEMP = TEMP_READ - 0.25 + ((REG_SLOPE - REG_COUNT) / REG_SLOPE) - -Note that this is what the DONE bit in the DS1621 configuration register is -good for: Internally, one temperature conversion takes up to 1000ms. Before -that conversion is complete you will not be able to read valid things out -of REG_COUNT and REG_SLOPE. The DONE bit, as you may have guessed by now, -tells you whether the conversion is complete ("done", in plain English) and -thus, whether the values you read are good or not. - -The DS1621 has two modes of operation: "Continuous" conversion, which can -be understood as the default stand-alone mode where the chip gets the -temperature and controls external devices via its Tout pin or tells other -i2c's about it if they care. The other mode is called "1SHOT", that means -that it only figures out about the temperature when it is explicitly told -to do so; this can be seen as power saving mode. - -Now if you want to read REG_COUNT and REG_SLOPE, you have to either stop -the continuous conversions until the contents of these registers are valid, -or, in 1SHOT mode, you have to have one conversion made. |