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Signed-off-by: Colin Ian King <colin.king@canonical.com> Acked-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
188 lines
6.4 KiB
Plaintext
188 lines
6.4 KiB
Plaintext
Kernel driver ds1621
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====================
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Supported chips:
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* Dallas Semiconductor / Maxim Integrated DS1621
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Prefix: 'ds1621'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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* Dallas Semiconductor DS1625
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Prefix: 'ds1625'
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Addresses scanned: none
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Datasheet: Publicly available from www.datasheetarchive.com
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* Maxim Integrated DS1631
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Prefix: 'ds1631'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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* Maxim Integrated DS1721
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Prefix: 'ds1721'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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* Maxim Integrated DS1731
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Prefix: 'ds1731'
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Addresses scanned: none
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Datasheet: Publicly available from www.maximintegrated.com
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Authors:
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Christian W. Zuckschwerdt <zany@triq.net>
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valuable contributions by Jan M. Sendler <sendler@sendler.de>
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ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
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with the help of Jean Delvare <jdelvare@suse.de>
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Module Parameters
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------------------
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* polarity int
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Output's polarity: 0 = active high, 1 = active low
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Description
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-----------
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The DS1621 is a (one instance) digital thermometer and thermostat. It has
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both high and low temperature limits which can be user defined (i.e.
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programmed into non-volatile on-chip registers). Temperature range is -55
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degree Celsius to +125 in 0.5 increments. You may convert this into a
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Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
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parameter is not provided, original value is used.
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As for the thermostat, behavior can also be programmed using the polarity
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toggle. On the one hand ("heater"), the thermostat output of the chip,
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Tout, will trigger when the low limit temperature is met or underrun and
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stays high until the high limit is met or exceeded. On the other hand
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("cooler"), vice versa. That way "heater" equals "active low", whereas
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"conditioner" equals "active high". Please note that the DS1621 data sheet
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is somewhat misleading in this point since setting the polarity bit does
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not simply invert Tout.
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A second thing is that, during extensive testing, Tout showed a tolerance
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of up to +/- 0.5 degrees even when compared against precise temperature
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readings. Be sure to have a high vs. low temperature limit gap of al least
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1.0 degree Celsius to avoid Tout "bouncing", though!
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The alarm bits are set when the high or low limits are met or exceeded and
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are reset by the module as soon as the respective temperature ranges are
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left.
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The alarm registers are in no way suitable to find out about the actual
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status of Tout. They will only tell you about its history, whether or not
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any of the limits have ever been met or exceeded since last power-up or
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reset. Be aware: When testing, it showed that the status of Tout can change
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with neither of the alarms set.
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Since there is no version or vendor identification register, there is
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no unique identification for these devices. Therefore, explicit device
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instantiation is required for correct device identification and functionality
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(one device per address in this address range: 0x48..0x4f).
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The DS1625 is pin compatible and functionally equivalent with the DS1621,
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but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are
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also pin compatible with the DS1621 and provide multi-resolution support.
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Additionally, the DS1721 data sheet says the temperature flags (THF and TLF)
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are used internally, however, these flags do get set and cleared as the actual
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temperature crosses the min or max settings (which by default are set to 75
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and 80 degrees respectively).
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Temperature Conversion:
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-----------------------
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DS1621 - 750ms (older devices may take up to 1000ms)
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DS1625 - 500ms
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DS1631 - 93ms..750ms for 9..12 bits resolution, respectively.
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DS1721 - 93ms..750ms for 9..12 bits resolution, respectively.
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DS1731 - 93ms..750ms for 9..12 bits resolution, respectively.
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Note:
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On the DS1621, internal access to non-volatile registers may last for 10ms
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or less (unverified on the other devices).
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Temperature Accuracy:
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---------------------
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DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees)
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DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees)
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DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees)
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DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees)
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DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees)
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Note:
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Please refer to the device datasheets for accuracy at other temperatures.
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Temperature Resolution:
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-----------------------
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As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution
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support, which is achieved via the R0 and R1 config register bits, where:
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R0..R1
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------
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0 0 => 9 bits, 0.5 degrees Celsius
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1 0 => 10 bits, 0.25 degrees Celsius
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0 1 => 11 bits, 0.125 degrees Celsius
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1 1 => 12 bits, 0.0625 degrees Celsius
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Note:
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At initial device power-on, the default resolution is set to 12-bits.
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The resolution mode for the DS1631, DS1721, or DS1731 can be changed from
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userspace, via the device 'update_interval' sysfs attribute. This attribute
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will normalize the range of input values to the device maximum resolution
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values defined in the datasheet as follows:
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Resolution Conversion Time Input Range
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(C/LSB) (msec) (msec)
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------------------------------------------------
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0.5 93.75 0....94
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0.25 187.5 95...187
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0.125 375 188..375
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0.0625 750 376..infinity
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------------------------------------------------
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The following examples show how the 'update_interval' attribute can be
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used to change the conversion time:
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$ cat update_interval
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750
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$ cat temp1_input
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22062
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$
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$ echo 300 > update_interval
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$ cat update_interval
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375
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$ cat temp1_input
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22125
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$
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$ echo 150 > update_interval
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$ cat update_interval
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188
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$ cat temp1_input
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22250
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$
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$ echo 1 > update_interval
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$ cat update_interval
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94
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$ cat temp1_input
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22000
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$
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$ echo 1000 > update_interval
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$ cat update_interval
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750
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$ cat temp1_input
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22062
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$
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As shown, the ds1621 driver automatically adjusts the 'update_interval'
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user input, via a step function. Reading back the 'update_interval' value
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after a write operation provides the conversion time used by the device.
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Mathematically, the resolution can be derived from the conversion time
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via the following function:
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g(x) = 0.5 * [minimum_conversion_time/x]
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where:
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-> 'x' = the output from 'update_interval'
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-> 'g(x)' = the resolution in degrees C per LSB.
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-> 93.75ms = minimum conversion time
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