Touchscreen filters in andy-tracking...

Andy Green andy at
Wed Jan 28 10:17:02 CET 2009

Hash: SHA1

Somebody in the thread at some point said:
| On Tue, Jan 27, 2009 at 8:05 PM, "Marco Trevisan (Treviño)"
| <mail at> wrote:
|> I've just give a try to this [1] kernel image in my Om2008 based
|> distro... I've read so much about the new LCD touchscreen filters and

| A few people contributed code/ideas for the touchscreen filtering. I
| tuned a few things and added a filter.

For the record, I wrote the bulk of it.

2.6.26 has the touchscreen filter stuff in, but not Nelson's filter that
discards samples after tap seen that replaces Tick and others' work in
the same area.

|> I'm saying this after that I've tested the touchscreen behavior writing
|> with the Illume keyboard.

|> So, with the stable kernel I can write very quickly with very low
|> pressure and generally I don't have precision issues.
|> At the contrary, using the 2.6.28 kernel I've to write really slowly
|> (using more pressure) and often it doesn't grabs fast double-clicks over
|> a region (needed when you write a letter with some double-chars or if
|> all the chars are near in the keyboard).

Marco is talking only about tap performance I think, and about having to
use "more pressure", I think what it actually means is "press longer"
since it is a tap action.  So this will be the discarding action of
first few samples on tap.  That is also impacting doubleclick then as he
describes, so I think he actually only has one small issue here with
early samples after touch detection being discarded.

Here's an idea for a patch that can improve performance there... at the
moment, we are able to run the touchscreen ADCs at slowest possible rate
due to the really good performance of mainly the median filter for
general tracking.

How about we increase ADC rate for the period shortly after touch is
detected?  Maybe it can help us get more information about touch
location quicker so we can do the filtering we currently take a lot of
time on more rapidly and hide that we are doing it.

| I thought it would be good to modify in order to make a
| survey and then an optimization. That is, with a calibrated

Maybe so.

- -Andy
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