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iio:core: mounting matrix support

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Expose a rotation matrix to indicate userspace the chip placement with
respect to the overall hardware system. This is needed to adjust
coordinates sampled from a sensor chip when its position deviates from the
main hardware system.

Final coordinates computation is delegated to userspace since:
* computation may involve floating point arithmetics ;
* it allows an application to combine adjustments with arbitrary
  transformations.

This 3 dimentional space rotation matrix is expressed as 3x3 array of
strings to support floating point numbers. It may be retrieved from a
"[<dir>_][<type>_]mount_matrix" sysfs attribute file. It is declared into a
device / driver specific DTS property or platform data.

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Gregor Boirie
2016-04-20 19:23:43 +02:00
committed by Jonathan Cameron
parent dc2c57153e
commit dfc57732ad
3 changed files with 164 additions and 0 deletions
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51
Documentation/ABI/testing/sysfs-bus-iio
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@@ -1512,3 +1512,54 @@ Contact: linux-iio@vger.kernel.org
Description:
Raw (unscaled no offset etc.) pH reading of a substance as a negative
base-10 logarithm of hydrodium ions in a litre of water.
What: /sys/bus/iio/devices/iio:deviceX/mount_matrix
What: /sys/bus/iio/devices/iio:deviceX/in_mount_matrix
What: /sys/bus/iio/devices/iio:deviceX/out_mount_matrix
KernelVersion: 4.6
Contact: linux-iio@vger.kernel.org
Description:
Mounting matrix for IIO sensors. This is a rotation matrix which
informs userspace about sensor chip's placement relative to the
main hardware it is mounted on.
Main hardware placement is defined according to the local
reference frame related to the physical quantity the sensor
measures.
Given that the rotation matrix is defined in a board specific
way (platform data and / or device-tree), the main hardware
reference frame definition is left to the implementor's choice
(see below for a magnetometer example).
Applications should apply this rotation matrix to samples so
that when main hardware reference frame is aligned onto local
reference frame, then sensor chip reference frame is also
perfectly aligned with it.
Matrix is a 3x3 unitary matrix and typically looks like
[0, 1, 0; 1, 0, 0; 0, 0, -1]. Identity matrix
[1, 0, 0; 0, 1, 0; 0, 0, 1] means sensor chip and main hardware
are perfectly aligned with each other.
For example, a mounting matrix for a magnetometer sensor informs
userspace about sensor chip's ORIENTATION relative to the main
hardware.
More specifically, main hardware orientation is defined with
respect to the LOCAL EARTH GEOMAGNETIC REFERENCE FRAME where :
* Y is in the ground plane and positive towards magnetic North ;
* X is in the ground plane, perpendicular to the North axis and
positive towards the East ;
* Z is perpendicular to the ground plane and positive upwards.
An implementor might consider that for a hand-held device, a
'natural' orientation would be 'front facing camera at the top'.
The main hardware reference frame could then be described as :
* Y is in the plane of the screen and is positive towards the
top of the screen ;
* X is in the plane of the screen, perpendicular to Y axis, and
positive towards the right hand side of the screen ;
* Z is perpendicular to the screen plane and positive out of the
screen.
Another example for a quadrotor UAV might be :
* Y is in the plane of the propellers and positive towards the
front-view camera;
* X is in the plane of the propellers, perpendicular to Y axis,
and positive towards the starboard side of the UAV ;
* Z is perpendicular to propellers plane and positive upwards.