topic lcd display image in different offset in i.MX Processors

lcd display image in different offset

rans — Thu, 03 Dec 2015 21:30:00 GMT

Hello,

I have configured a 240x320 LCD with timing correcpond to 240 pixel line and 512 lines (instead of 320). Any other configuration did not work with my LCD.

Now I can finally get a stable image , but each time the image starts at different line (and the rest of the screen is blank).

on doing:

dd if=/dev/zero of=/dev/fb0

It resolved this issue.

Does anyone anyone knows why the above command resolve the problem ? I would assume that framebuffer content is the same even before doing this command, so i don't understand the effect.

I also do not understand what the reason for the different line offset in the first place.

Thanks,

Ran

Re: lcd display image in different offset

Yuri — Fri, 04 Dec 2015 03:50:51 GMT

Hello,

Looks like the LCD was not fully correctly in initialized.

Please look at app note AN3974 “Different Display Configurations on

i.MX35 Linux PDK” describing display parameters for initialization.

http://cache.freescale.com/files/dsp/doc/app_note/AN3974.pdf

Have a great day,
Yuri

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Re: lcd display image in different offset

rans — Fri, 04 Dec 2015 06:11:22 GMT

Hi Yuri,

Thank you for the suggestion and link.

But why did the following command seems to redsolved the issue

dd if=/dev/zero of=/dev/fb0

What effect does it have, and does it imply that the timing are correct ?

Regards,

Ran

Re: lcd display image in different offset

rans — Sat, 05 Dec 2015 10:44:50 GMT

Hi,

I wanted to add that framebuffer is configured as following:

fbset -fb /dev/fb0 -xres 240 -yres 320 -vxres 240 -vyres 320

so, I don't know why

dd if=/dev/zero of=/dev/fb0

results in image correct display starting with line 0 on the screen.

I think that writing to framebuffer should fill the complete buffer.

Regards,

Ran

Re: lcd display image in different offset

Yuri — Wed, 09 Dec 2015 04:43:31 GMT

Hello,

I do not think, that clearing frame buffer fully resolve the issue, if timings are

not correct.

Regards,
Yuri.