Hi Vandana,
I've been doing some testing with the Synaptics rmi4 driver that supports
the touch API. I finally got a result, but it requires a bit of work in the
vivid driver (and v4l2-ctl) because it means that vivid should use a different
touch format to match what this driver returns.
Some background (based on what I understood from the driver): the Synaptics
driver is used for touchpads on laptops. The touch API itself is meant for
diagnostics only, and not for regular use. It 'captures' 21x12 points ('pixels')
as an image containing the capacitance measurements.
It looks as if typically not all measuring points are available, instead only a
subset is actually returning valid values in this diagnostic module.
Which points are available is reported in 'Function 55', which my Synaptics
touchpad does not support, so instead the touch API falls back to the default
of 21x12. Looking at the values I receive it appears that on my laptop only
part of the bottom set of points in the touchpad is made available (16x1).
Alternatively, this could be just a driver bug (I really do not trust the driver,
I doubt it sees much testing so it could very well be a regression).
In any case, this is sufficient to see what sort of data values are used.
This is with input 0 of the v4l-touch0 device which uses this format:
https://hverkuil.home.xs4all.nl/spec/uapi/v4l/pixfmt-tch-td16.html
Also, this format returns the data in little endian format. I suspect that
the documentation for this touch formats is wrong since that indicates big-endian.
So vivid/v4l2-ctl should be modified to use this instead of V4L2_TCH_FMT_TU16.
Below is a dump of what happens if I move my finger from left to right. Each
line is a single frame. As you can see, the background values are around 0.
When pressed that max value is around 200 and you see a small Bell-curve
of lower values around it stretching 3-4 points.
I'm not sure if it is worth reproducing that Bell curve in vivid, I think it
is OK to just set a single value. The background noise can be something like
a random number between -3 and 3, and the pressure point a random number between
200-220.
Regards,
Hans
-2 -4 -2 -2 -3 -3 -3 -3 -4 -5 -5 -5 -3 -4 -4 -4
1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
-2 -3 -2 -2 -3 -4 -3 -4 -4 -3 -4 -4 -4 -4 -3 -4
13 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1
49 0 -2 -2 -2 -4 -3 -4 -4 -5 -5 -4 -3 -4 -4 -3
201 65 3 0 0 0 0 0 0 0 0 0 0 0 0 0
191 143 3 -2 -2 -3 -3 -4 -5 -5 -5 -5 -4 -5 -4 -5
198 155 8 1 0 0 0 0 0 0 0 0 1 0 1 0
190 159 5 -1 -2 -3 -3 -3 -4 -5 -4 -6 -4 -5 -4 -6
145 214 56 1 1 0 0 0 0 0 0 0 1 0 0 2
90 211 91 0 -2 -3 -3 -4 -4 -5 -3 -5 -3 -4 -4 -4
32 203 171 12 2 0 0 0 0 0 1 0 1 0 1 0
0 71 211 143 2 -3 -3 -3 -3 -3 -3 -3 -2 -3 -3 -3
1 18 193 209 31 1 1 0 0 0 0 0 0 0 0 0
-2 15 192 206 29 -2 -2 -2 -4 -3 -4 -4 -3 -3 -4 -3
2 21 197 215 37 2 1 0 0 0 0 0 0 0 0 0
-2 15 190 209 33 -1 -3 -3 -4 -4 -4 -4 -3 -4 -3 -4
0 3 100 220 153 6 1 0 0 0 0 0 1 0 0 0
-3 -2 20 200 211 35 -1 -2 -3 -3 -2 -4 -3 -3 -2 -2
0 0 6 150 222 105 3 0 0 0 1 0 1 0 0 1
-4 -4 -2 35 208 192 24 -1 -4 -3 -2 -3 -2 -3 -3 -2
0 0 1 35 212 198 29 1 0 0 0 0 0 0 0 0
-3 -3 -2 3 157 198 93 0 -3 -3 -3 -3 -2 -3 -3 -2
0 0 0 0 30 191 197 44 1 0 1 0 2 1 1 1
-3 -4 -3 -3 -1 66 192 182 8 -2 -2 -4 -3 -3 -3 -3
0 0 0 0 0 5 133 212 134 5 1 1 1 1 1 1
-3 -5 -3 -5 -4 -3 19 191 208 51 -1 -4 -3 -4 -3 -3
1 0 0 0 0 0 6 141 212 133 6 1 2 1 2 2
-4 -4 -3 -4 -4 -4 -1 48 206 198 19 -3 -2 -4 -3 -3
0 0 0 0 0 0 0 3 112 214 162 6 1 1 2 1
-3 -4 -4 -5 -5 -4 -3 -2 9 175 202 66 -1 -3 -3 -3
0 0 0 0 0 0 0 0 2 63 205 205 22 1 1 1
-3 -5 -2 -4 -4 -4 -4 -4 -3 28 191 214 40 -2 -3 -5
0 0 0 0 0 0 0 0 0 14 169 223 86 3 1 1
-3 -4 -3 -4 -4 -3 -3 -4 -4 -1 58 213 184 7 -2 -3
0 0 0 0 0 0 0 0 0 0 10 200 225 83 2 1
-4 -5 -4 -5 -5 -5 -5 -4 -5 -4 1 165 218 105 0 -4
0 0 0 0 0 0 0 0 0 0 2 76 222 192 13 1
-3 -4 -4 -4 -5 -5 -4 -4 -5 -6 -5 -1 107 214 149 0
0 0 0 0 0 0 0 0 0 0 0 0 14 181 211 83
-3 -4 -3 -4 -4 -4 -3 -4 -4 -4 -4 -4 0 54 205 191
0 0 0 0 0 0 0 0 0 0 0 0 1 7 136 210
-3 -4 -4 -4 -5 -5 -5 -4 -5 -4 -4 -5 -4 -3 14 179
0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 74
-3 -4 -3 -5 -4 -5 -4 -4 -4 -4 -5 -6 -5 -4 -4 -1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-3 -4 -3 -3 -4 -4 -3 -4 -5 -5 -5 -5 -5 -4 -4 -4
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-3 -4 -3 -4 -4 -5 -4 -4 -4 -5 -5 -6 -5 -5 -4 -4
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
-3 -4 -3 -4 -4 -4 -4 -4 -5 -4 -5 -6 -4 -5 -5 -5
0 0 0 0 0 0 0 0 -1 -1 0 -1 0 -1 0 0
-3 -4 -2 -4 -3 -4 -4 -4 -4 -4 -4 -5 -4 -5 -3 -3
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
