Noise from touchscreen controller after upgrade to newer TI SDK

Steve Ziuchkovski

Other Parts Discussed in Thread: AM3358

First a little history: Our product uses an AM3358 with a 4.3 LCD and 4-wire resistive touch panel. We had an issue where there were a LOT of false touches being detected by the Linux driver (the driver shipped by TI in the 07.00.00.00 Sitara SDK with kernel 3.12). We were able to determine that this was cause by noise coupling over into the touchscreen from the LCD - if we draw a black screen, no false touches were registered, but if we drew a screen with varying colors of pixels (like a which background with a black grid and text), there would be significant noise coupled over. We resolved this at the time by grounding the metal chassis of the LCD to the metal chassis of our product.

Fast forward a bit, and I've now updated out system to use the newer 01.00.00.03 Processor SDK, which includes a new kernel (3.14) and a newer touchscreen driver. The problem is now back, although not quite as badly (false touches seems to be focused on the lower-right corner of the touchscreen). If I switch between an older version of our software and the newer version with the new driver, I can make the problem come and go - so software definitely has a role in this.

In the device-tree binding documentation, there is a new setting for the newer driver, "ti,charge-delay". It was set to 0xb000, and I've tried 0x0400 and 0xFFFF, b it doesn't seem to have any effect.

Also, I did a web search and noticed that the device tree binding documentation that's on kernel.org has quite a bit more options listed than in the version from the Processor SDK. Why is this? I can't help but think that some of those options might apply here: chan-step-opendelay, chan-step-sampledelay, and chan-step-avg.

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

I will ask the ADC experts to check this.

0 Wolfgang Muees1 over 10 years ago

Genius 3685 points

Noise from the LCD is a common problem for resistive touches, and every touch controller has to be noise-hardened.

Unfortunately, the TI TSADC pen detection has no noise filter build in. Broken by design....

I have done a rewrite of the touch driver, implementing a pen detection in software.
It's for Linux 3.16. Attached to this post. Feel free to use it.

regards

Wolfgangtsc_linux_3_16.tar.gz

0 Steve Ziuchkovski over 10 years ago in reply to Wolfgang Muees1

Expert 1255 points

Wolfgang Muees1 said:

Unfortunately, the TI TSADC pen detection has no noise filter build in. Broken by design....

Thanks, I'll take a look at it. I'm still wondering why an older TI driver worked better (meaning: worked).

0 Wolfgang Muees1 over 10 years ago in reply to Steve Ziuchkovski

Genius 3685 points

I started with the ADC driver in Linux 3.2. And I got pen detection problems because of noise on a 4,3" TFT.
"Better" was not good enough.

0 Cash Chang over 10 years ago in reply to Wolfgang Muees1

Prodigy 40 points

Hi Wolfgang,

Thanks for your great work on touch improvement.

I also got the penup problem on SDK7.0 and boneblack liked platform. so I try use your code on my platform even the kernel version is 3.12

There is no any error and warning during compile. I using ts_print_raw to test the new driver. but the X and Y always 0 and the coordinate not repeat

when pen down.

I am not sure the DT should be modify or not. I don't know how to solve it. Please help.

Thank you very much.

Regards,

Cash

0 Wolfgang Muees1 over 10 years ago in reply to Cash Chang

Genius 3685 points

Device tree:

&tscadc {
	status = "okay";
	tsc {
		ti,wires = <4>;
		ti,x-plate-resistance = <200>;
		ti,coordinate-readouts = <5>;
		ti,wire-config = <0x00 0x11 0x22 0x33>;
		ti,x-axis = <0 480 1>;
		ti,y-axis = <0 272 1>;
	};

	adc {
		ti,adc-channels = <4 5 6 7>;
	};
};

0 Cash Chang over 10 years ago in reply to Wolfgang Muees1

Prodigy 40 points

Hi Wolfgang,

Thanks for your reply.

I found the problem in process_samples() routine, because the they are both 0 in ts_dev->x.offset and x.scale, Y also 0 in calculate screen coordinates section.

That is way I got X,Y are 0 after calculation.

When I marked these codes, and calibrate my touch by tslib. Everything working well, it is no more strange penup events. but I am not sure it is OK on Android.

Thanks for your great job.

BR,

Cash

0 Wolfgang Muees1 over 10 years ago in reply to Cash Chang

Genius 3685 points

Ah,
the offset and scale variables are used to do touch screen calibration via sysfs. Please read www.kernel.org/.../sysfs.txt. In this way, you can do touch screen calibration in android without reboot.

We use this driver in android 4.3 and 4.4.

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Noise from touchscreen controller after upgrade to newer TI SDK