4dcape-70t lcd and jitter issues

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1

Hello,

I tried the latest kernel from git://github.com/beagleboard/kernel.git
that contains Mikka's patch to fix the jitter on lcd7 and 4dcape-70t
and I noticed the following:

When I start the system, once I touch the screen, hexdump
/dev/input/event1 starts dumping data without stopping.

In tslib (ts_test), the cursor "goes" to the bottom left corner.

As soon as I issue an
echo1 > /sys/class/graphics/fb0/blank
the data from /dev/input/event1 stops.

This behavior persists until the screen blanks on its own (tilcdc
4830e000.fb: timeout waiting for framedone)

After that, the screen becomes usable however there is still jitter.
There seems to be an event generated at the bottom left corner.

The screen was calibrated with ts_calibrate.

I have tested the latest debian image from RCN and the same issue is present.

In this image, the screen was calibrated when X started.

Can other people confirm this ? So far I tried this with two
4DCape-70T. LCD7 from CircuitCo does not have this issue.

2

Hello all,

I forgot to mention that adding a udelay of 5 microseconds seems to
make the issue go away:

diff --git a/drivers/input/touchscreen/ti_am335x_tsc.c
b/drivers/input/touchscreen/ti_am335x_tsc.c
index ed83043..e1c0499 100644
--- a/drivers/input/touchscreen/ti_am335x_tsc.c
+++ b/drivers/input/touchscreen/ti_am335x_tsc.c
@@ -227,6 +227,7 @@ static void titsc_read_coordinates(struct titsc *ts_dev,
        nY=0;
        for (i = 0; i < fifocount; i++) {
                read = titsc_readl(ts_dev, REG_FIFO0);
+ udelay(5);

                channel = (read & 0xf0000) >> 16;
                read &= 0xfff;

So this bug seems to be related perhaps to synchronization issues, I
do not know. I noticed that the bug went away when I added printk
statements. Unfortunately, that does not help me with the debugging.

If anybody has any ideas, let me know.

Cheers,

Alex

3

Alex, can you help me, I have the exact same issue. Could you upload your image that fixes the issue with the 5 micro seconds delay. Are you running debian or Ubuntu? I am not an expert on rebuilding the kernel to change the ti_am335x_tsc.c.

Thanks

4

Hi Daniel,

Alex, can you help me, I have the exact same issue. Could you upload your
image that fixes the issue with the 5 micro seconds delay. Are you running
debian or Ubuntu? I am not an expert on rebuilding the kernel to change the
ti_am335x_tsc.c.

I use debian and angstrom.

I modified RCN's kernel with a 15 microsecond hack.

I'll email you directly the contents of deploy:

3.8.13-bone40.1-dtbs.tar.gz
3.8.13-bone40.1-modules.tar.gz
config-3.8.13-bone40.1
3.8.13-bone40.1-firmware.tar.gz
3.8.13-bone40.1.zImage

Cheers,

Alex

5

Any chance you could upload a full image file of debian with your fix to a site like drop box or something? One that I could use Win32DiskImager to burn to a 4 gig micro sd card?

I would really appreciate it.

Thanks.

Dan

6

Alex, it appears your files are working. I can’t thank you enough for the patch. I simply replaced all the files by mounting a previous SD card image and copying all the files to the appropriate locations. Your code fixes the issue. Again thanks thanks thanks.

Dan

7

Hi Dan,

Glad it worked.

It is still a hack and there is most probably a better solution. I
still get some random clicks in the bottom left corner from time to
time.

Cheers,

Alex