Re: How should Touchscreen Input Drives behave (OpenEZX pcap_ts)

From: Harald Welte
Date: Thu May 18 2006 - 10:44:53 EST

On Thu, May 18, 2006 at 01:16:16PM +0200, Florent Thiery wrote:
> > As of now, I return
> > X_ABS, Y_ABS and PRESSURE values between 0 and 1000 (each).
> >
> Are you kidding ??? Does the touchscreen support pressure sensitivity?
> Normally it wouldn't, you'd have only two values... Because
> sensitivity touchscreens really are rare... That's why wacom does
> use the pen to report pressure info on their tablets

No, this touchscreen actually has fairly reasonable pressure reporting.
I know that this is unusual. But I get reproducible numbers when trying
soft stylus press, hard stylus press. And things like finger touching.
Also I can actually distinguish a thumb from an index finger press ;)

> >1) where does touchscreen calibration happen? The EZX phones (like many
> > other devices, I believe) only contain resistive touchscreens that
> > appear pretty uncalibrated. I'm sure the factory-set calibration
> > data must be stored somewhere in flash, but it's definitely handled
> > in the proprietary EZX userland, since their old kernel driver
> > doesn't have any calibration related bits.
> >
> I would say touchscreen calibration = scaling (to resolution) + reference points

see the other comments. apparently that is left to userspace.

> I would say the best would be to watch pressure evolution.... If it
> springs from 0 to 400 in less than sotg like 200 ms, then you got the
> "button" event. Is it feasable?

that would require rerlatively small polling intervals. please note
that the hardware generates interrupts when pressure != 0. We could
start a high-granularity timer

> I got a question: does stylus usage on original A780 show the pressure
> sensitivity?

not that I've ever noted. But Motorola ignores many of the hardwares

> Another one: you say you're workin on building X-e. Are you talking about kdrive?

I have no idea, just replaying the package names that OE uses ;)

I now have Xfbdev running on the A780. Unfortunately due to some
strange black magic, the ts driver ceases to receive interrupts as soon
as X is started. reproducible. The same happens with ts_test.

ts_print works very good, though.

Will do more debugging

- Harald Welte <laforge@xxxxxxxxxxxx>
We all know Linux is does infinite loops in 5 seconds. -- Linus

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