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Diffstat (limited to 'Documentation/hwmon/ds1621')
| -rw-r--r-- | Documentation/hwmon/ds1621 | 197 |
1 files changed, 138 insertions, 59 deletions
diff --git a/Documentation/hwmon/ds1621 b/Documentation/hwmon/ds1621 index 1fee6f1e6bc..f775e612f58 100644 --- a/Documentation/hwmon/ds1621 +++ b/Documentation/hwmon/ds1621 @@ -2,22 +2,36 @@ Kernel driver ds1621 ==================== Supported chips: - * Dallas Semiconductor DS1621 + * Dallas Semiconductor / Maxim Integrated DS1621 Prefix: 'ds1621' - Addresses scanned: I2C 0x48 - 0x4f - Datasheet: Publicly available at the Dallas Semiconductor website - http://www.dalsemi.com/ + Addresses scanned: none + Datasheet: Publicly available from www.maximintegrated.com + * Dallas Semiconductor DS1625 - Prefix: 'ds1621' - Addresses scanned: I2C 0x48 - 0x4f - Datasheet: Publicly available at the Dallas Semiconductor website - http://www.dalsemi.com/ + Prefix: 'ds1625' + Addresses scanned: none + Datasheet: Publicly available from www.datasheetarchive.com + + * Maxim Integrated DS1631 + Prefix: 'ds1631' + Addresses scanned: none + Datasheet: Publicly available from www.maximintegrated.com + + * Maxim Integrated DS1721 + Prefix: 'ds1721' + Addresses scanned: none + Datasheet: Publicly available from www.maximintegrated.com + + * Maxim Integrated DS1731 + Prefix: 'ds1731' + Addresses scanned: none + Datasheet: Publicly available from www.maximintegrated.com Authors: Christian W. Zuckschwerdt <zany@triq.net> valuable contributions by Jan M. Sendler <sendler@sendler.de> ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net> - with the help of Jean Delvare <khali@linux-fr.org> + with the help of Jean Delvare <jdelvare@suse.de> Module Parameters ------------------ @@ -49,12 +63,9 @@ 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 @@ -62,47 +73,115 @@ any of the limits have ever been met or exceeded since last power-up or reset. Be aware: When testing, it showed that the status of Tout can change 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. +Since there is no version or vendor identification register, there is +no unique identification for these devices. Therefore, explicit device +instantiation is required for correct device identification and functionality +(one device per address in this address range: 0x48..0x4f). + +The DS1625 is pin compatible and functionally equivalent with the DS1621, +but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are +also pin compatible with the DS1621 and provide multi-resolution support. + +Additionally, the DS1721 data sheet says the temperature flags (THF and TLF) +are used internally, however, these flags do get set and cleared as the actual +temperature crosses the min or max settings (which by default are set to 75 +and 80 degrees respectively). + +Temperature Conversion: +----------------------- +DS1621 - 750ms (older devices may take up to 1000ms) +DS1625 - 500ms +DS1631 - 93ms..750ms for 9..12 bits resolution, respectively. +DS1721 - 93ms..750ms for 9..12 bits resolution, respectively. +DS1731 - 93ms..750ms for 9..12 bits resolution, respectively. + +Note: +On the DS1621, internal access to non-volatile registers may last for 10ms +or less (unverified on the other devices). + +Temperature Accuracy: +--------------------- +DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees) +DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees) +DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees) +DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees) +DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees) + +Note: +Please refer to the device datasheets for accuracy at other temperatures. + +Temperature Resolution: +----------------------- +As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution +support, which is achieved via the R0 and R1 config register bits, where: + +R0..R1 +------ + 0 0 => 9 bits, 0.5 degrees Celcius + 1 0 => 10 bits, 0.25 degrees Celcius + 0 1 => 11 bits, 0.125 degrees Celcius + 1 1 => 12 bits, 0.0625 degrees Celcius + +Note: +At initial device power-on, the default resolution is set to 12-bits. + +The resolution mode for the DS1631, DS1721, or DS1731 can be changed from +userspace, via the device 'update_interval' sysfs attribute. This attribute +will normalize the range of input values to the device maximum resolution +values defined in the datasheet as follows: + +Resolution Conversion Time Input Range + (C/LSB) (msec) (msec) +------------------------------------------------ +0.5 93.75 0....94 +0.25 187.5 95...187 +0.125 375 188..375 +0.0625 750 376..infinity +------------------------------------------------ + +The following examples show how the 'update_interval' attribute can be +used to change the conversion time: + +$ cat update_interval +750 +$ cat temp1_input +22062 +$ +$ echo 300 > update_interval +$ cat update_interval +375 +$ cat temp1_input +22125 +$ +$ echo 150 > update_interval +$ cat update_interval +188 +$ cat temp1_input +22250 +$ +$ echo 1 > update_interval +$ cat update_interval +94 +$ cat temp1_input +22000 +$ +$ echo 1000 > update_interval +$ cat update_interval +750 +$ cat temp1_input +22062 +$ + +As shown, the ds1621 driver automatically adjusts the 'update_interval' +user input, via a step function. Reading back the 'update_interval' value +after a write operation provides the conversion time used by the device. + +Mathematically, the resolution can be derived from the conversion time +via the following function: + + g(x) = 0.5 * [minimum_conversion_time/x] + +where: + -> 'x' = the output from 'update_interval' + -> 'g(x)' = the resolution in degrees C per LSB. + -> 93.75ms = minimum conversion time |