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drivers/misc: support for the pressure sensor BMP085 from Bosch Sensortec

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This driver adds support for the BMP085 digital pressure sensor from Bosch
Sensortec.  It exposes a sysfs api to userspace where pressure and
temperature measurement results can be read from the pressure0_input and
temp0_input file.  The chip is able to calculate the average of up to
eight samples to increase the accuracy.  This feature can be controlled by
writing to the oversampling file.

The BMP085 digital pressure sensor can measure ambient air pressure and
temperature.  Both values can be obtained from sysfs files.  The pressure
is measured by reading from pressure0_input.  Valid values range from
30000 to 110000 pascal with a resolution of 1 pascal (=0.01 millibar).

temp0_input holds the current temperature in degree celsius, multiplied by
10.  This results in a resolution of a tenth degree celsius.  Values range
from -400 to 850.

To increase the accuracy, this chip can calculate the average of 1, 2, 4
or 8 samples.  This behavior is controlled through the oversampling sysfs
file.  Two to the power of the value written to that file specifies how
many samples will be used.  Valid values: 0..3.

[[email protected]: fix typo]
[[email protected]: optimize the wait time for the pressure sensor, definition of long is arch dependent so make it u32]
[[email protected]: coding-style fixes]
Signed-off-by: Christoph Mair <[email protected]>
Signed-off-by: Shubhrajyoti D <[email protected]>
Acked-by: Jonathan Cameron <[email protected]>
Cc: Stefan Schmidt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Christoph Mair 2010-08-09 17:20:28 -07:00 • committed by Linus Torvalds
commit 5bf1d290b5
4 changed files with 524 additions and 0 deletions
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Documentation/ABI/testing/sysfs-i2c-bmp085 Normal file
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What: /sys/bus/i2c/devices/<busnum>-<devaddr>/pressure0_input
Date: June 2010
Contact: Christoph Mair <[email protected]>
Description: Start a pressure measurement and read the result. Values
represent the ambient air pressure in pascal (0.01 millibar).
Reading: returns the current air pressure.
What: /sys/bus/i2c/devices/<busnum>-<devaddr>/temp0_input
Date: June 2010
Contact: Christoph Mair <[email protected]>
Description: Measure the ambient temperature. The returned value represents
the ambient temperature in units of 0.1 degree celsius.
Reading: returns the current temperature.
What: /sys/bus/i2c/devices/<busnum>-<devaddr>/oversampling
Date: June 2010
Contact: Christoph Mair <[email protected]>
Description: Tell the bmp085 to use more samples to calculate a pressure
value. When writing to this file the chip will use 2^x samples
to calculate the next pressure value with x being the value
written. Using this feature will decrease RMS noise and
increase the measurement time.
Reading: returns the current oversampling setting.
Writing: sets a new oversampling setting.
Accepted values: 0..3.