mirror of
https://github.com/torvalds/linux.git
synced 2024-11-12 15:11:50 +00:00
ede7fbdf52
Part 3: Move the drivers documentation, plus two general documentation files. Note that the patch "adds trailing whitespace", because it does move the files as-is, and some files happen to have trailing whitespace. Signed-off-by: Jean Delvare <khali@linux-fr.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
109 lines
4.9 KiB
Plaintext
109 lines
4.9 KiB
Plaintext
Kernel driver ds1621
|
|
====================
|
|
|
|
Supported chips:
|
|
* Dallas Semiconductor DS1621
|
|
Prefix: 'ds1621'
|
|
Addresses scanned: I2C 0x48 - 0x4f
|
|
Datasheet: Publicly available at the Dallas Semiconductor website
|
|
http://www.dalsemi.com/
|
|
* Dallas Semiconductor DS1625
|
|
Prefix: 'ds1621'
|
|
Addresses scanned: I2C 0x48 - 0x4f
|
|
Datasheet: Publicly available at the Dallas Semiconductor website
|
|
http://www.dalsemi.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>
|
|
|
|
Module Parameters
|
|
------------------
|
|
|
|
* polarity int
|
|
Output's polarity: 0 = active high, 1 = active low
|
|
|
|
Description
|
|
-----------
|
|
|
|
The DS1621 is a (one instance) digital thermometer and thermostat. It has
|
|
both high and low temperature limits which can be user defined (i.e.
|
|
programmed into non-volatile on-chip registers). Temperature range is -55
|
|
degree Celsius to +125 in 0.5 increments. You may convert this into a
|
|
Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
|
|
parameter is not provided, original value is used.
|
|
|
|
As for the thermostat, behavior can also be programmed using the polarity
|
|
toggle. On the one hand ("heater"), the thermostat output of the chip,
|
|
Tout, will trigger when the low limit temperature is met or underrun and
|
|
stays high until the high limit is met or exceeded. On the other hand
|
|
("cooler"), vice versa. That way "heater" equals "active low", whereas
|
|
"conditioner" equals "active high". Please note that the DS1621 data sheet
|
|
is somewhat misleading in this point since setting the polarity bit does
|
|
not simply invert Tout.
|
|
|
|
A second thing is that, during extensive testing, Tout showed a tolerance
|
|
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 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
|
|
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.
|