okenido
Posts: 21
Joined: Thu Aug 02, 2018 11:47 am

Touch screen sensitivity for official 7" screen (rpi-ft5406)

Sun Oct 21, 2018 1:03 pm

Hello,

I noticed all touch screens supported by the Raspberry Pi in boot/overlays/ have a sensitivity parameter (see https://github.com/raspberrypi/firmware ... t/overlays), but there is no such option for the official 7" inch screen which uses a FT5406 controller:

Code: Select all

Name:   rpi-ft5406
Info:   Official Raspberry Pi display touchscreen
Load:   dtoverlay=rpi-ft5406,<param>=<val>
Params: touchscreen-size-x      Touchscreen X resolution (default 800)
        touchscreen-size-y      Touchscreen Y resolution (default 600);
        touchscreen-inverted-x  Invert touchscreen X coordinates (default 0);
        touchscreen-inverted-y  Invert touchscreen Y coordinates (default 0);
        touchscreen-swapped-x-y Swap X and Y cordinates (default 0);
Is there a hardware limitation that could explain this parameter is missing for this screen ? is there any way to set the sensitivity through mailboxes or direct I2C communication ?
I'm asking this since I find the sensitivity a bit low. Most of time it's working, but under some circumstances light finger presses are ignored

okenido
Posts: 21
Joined: Thu Aug 02, 2018 11:47 am

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Sun Oct 21, 2018 7:41 pm

Another problem I noticed : If my finger approach the screen slowly before entering in contact, the touch screen doesn't detect the press. If i'm slow enough, I can get to a quite high pressure with my finger and move it on a few centimeters on the screen without triggering any event.

That doesn't happen on my smartphone for example, even with the slowest approach I can do.

It looks like some adaptative-auto-threshold thing.. weird.

Is it possible to have more option about touchscreen through config.txt ?
Last edited by okenido on Sun Oct 21, 2018 9:12 pm, edited 1 time in total.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 20712
Joined: Sat Jul 30, 2011 7:41 pm

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Sun Oct 21, 2018 9:08 pm

Hmm. The driver for the official LCD touchscreen is on the GPU, so inaccessible. I'd need to make some changes to support this.

I'll take a look Monday to see if it is feasible.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

okenido
Posts: 21
Joined: Thu Aug 02, 2018 11:47 am

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Sun Oct 21, 2018 9:15 pm

Sorry I edited my last post, seeing I2C communication with the chip isn't directly possible.

Maybe the problem about slow touch presses being ignored is related to some sensitivity parameter too. Anyway, thanks for taking my request into account ;)

jamesh
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Raspberry Pi Engineer & Forum Moderator
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Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Mon Oct 22, 2018 10:47 am

Hmm, do appear to be some registers for sensitivity available on the FT5426, but they return 0 in my tests, might depend on whether we are using the 5406 or the 5426 (I believe we use both). I can try setting them but not sure if I would notice any changes.
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Please direct all questions to the forum, I do not do support via PM.

jamesh
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Raspberry Pi Engineer & Forum Moderator
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Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Mon Oct 22, 2018 12:17 pm

OK, tried setting the sensitivity pararmeter to 1, then 200 (max 255). I could not detect any difference in the 'sensitivity` of the touches - they were really quite sensitive at either end of the range - I hardly need to touch the display for the press to be detected.

So not sure if there is anything I can do here.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

okenido
Posts: 21
Joined: Thu Aug 02, 2018 11:47 am

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Mon Oct 22, 2018 2:57 pm

Image

I noticed with a multimeter that those I2C pins on the display PCB are directly connected to the FT5406, but the RPI doesn't need them since it controls it through the ribbon cable. Is it possible to disable the automatic touch screen handling (option in config.txt ?) so I can do my own I2C communication with the chip ? I guess there will be conflicts if the GPU is talking to it at the same time I do.

The current touch screen is quite good, I just want to see if I can get a better behavior on those edge cases by using custom parameters. It doesn't always register my light finger presses. Maybe it has something to do with skin, temperature and moisture too.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 20712
Joined: Sat Jul 30, 2011 7:41 pm

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Mon Oct 22, 2018 3:51 pm

okenido wrote:
Mon Oct 22, 2018 2:57 pm
Image

I noticed with a multimeter that those I2C pins on the display PCB are directly connected to the FT5406, but the RPI doesn't need them since it controls it through the ribbon cable. Is it possible to disable the automatic touch screen handling (option in config.txt ?) so I can do my own I2C communication with the chip ? I guess there will be conflicts if the GPU is talking to it at the same time I do.

The current touch screen is quite good, I just want to see if I can get a better behavior on those edge cases by using custom parameters. It doesn't always register my light finger presses. Maybe it has something to do with skin, temperature and moisture too.
I did try different parameters and saw no difference.

I'll post more details later, need to go catch train.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 20712
Joined: Sat Jul 30, 2011 7:41 pm

Re: Touch screen sensitivity for official 7" screen (rpi-ft5406)

Mon Oct 22, 2018 8:17 pm

OK, so there is an inhernet problem with accessing that particular I2C bus from ARM space, in that if the VC4 is connected to it, then I2C interrupts tend to be grabbed by the VC4 before the ARM (its interrupt system is quicker), and the ARM I2C driver goes pear shaped.

So the I2C need to be disabled on the VC4, which will in turn disable LCD setup, backlight, camera actions etc, as they all on that bus. A bit of a catch-22.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

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