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still the LCD NOISE problem.

YJ Liu
Expert 1675 points

Hi,all:

i have read this post:

http://processors.wiki.ti.com/index.php/TMS320DM355_High-Definition_(HD)_Display

and somebody say set the PBBPR register can solve this problem. I did as they say, But still has the NOISE.

My board is DM355@216MHz + DDR2 135MHz,I haven't  run the encode and decode demo , Just use a 800x480' LCD and running QT4.7.

When QT start the LCD has horizontal line flickering, After GUI start up when I touch the Widget Or Move the Window ,the horizontal flickering line (or BLOCK) also display. if I do nothing, it displays well.

I have tried to set the PBBPR to 0x10 to 0x30, But it doesn't work.

How to solve this?

  • 0
    TI__Mastermind 41665 points

    Trying various PBBPR values is one good idea to try to fix this as you suggest, but PBBPR cannot always fix the bandwidth limitations in the device, there are a couple of other things you can try though.

    1. If possible use a higher speed DDR2, the limitation you are running into is DDR2 bandwidth, so adding more of it would likely reduce the noise.

    2. Reduce the loading on your DDR2 bus from the processor by limiting what else may be running in the background, anything accessing the DDR2 has the potential to conflict with the display driver and cause the horizontal flickering line artifacts. It is possible that QT is not efficient enough to run at your resolution and frame rate without noise.

    3. Adjust your display driver settings to minimize the DDR2 bandwidth it is consuming, in particular disable or minimize any OSD windows other than the one you are filling for QT, even if they are on in the back ground they can be taking up DDR bandwidth. As discussed on the article you point out, minimizing the area of the OSD windows you are not using is critical to freeing up bandwidth for the display to operate.

    4. If possible, lower the frame rate you are driving your LCD with, lower frame rates on the VPBE will mean lower DDR2 bandwidth requirements and a lower probability of display artifacts.

    If all else fails you may want to consider migrating to a higher end device, such as DM365 or DM368 if you want something similar to the DM355 but with more performance, or a OMAP35x/DM37x device if you want even more ARM and graphics performance (though with less powerful video codec acceleration).

  • 0 in reply to Bernie Thompson TI
    Expert 1675 points

    thanks for replying.

    1. my board can only run to 132Mhz :(

    2.no other programs run at the same time

    3.I try to remove other 3 framebuffer, and it seems better, but still has some noise. I will try other methods.

    4.frame rate is only 30FPS :(

    5. that's another question I want to know:

    Does DM365 has the same LCD NOISE problem?

    Because We will update our system form MPEG4 to H264. But if DM365 still has the NOISE, we will consider it again.

    Thanks again.

  • 0 in reply to YJ Liu
    TI__Mastermind 41665 points

    liu yaojin said:
    Does DM365 has the same LCD NOISE problem?

    While I believe it is possible to cause the DM365 to have similar noise, it is not something I have seen in general,  the DM365 runs far more reliably at higher resolutions and rates without display artifacts due to DDR2 bandwidth saturation. The DM365 has significantly more bandwidth available and so it tends to not have this sort of display problem, this is one of the significant advances that came with the DM365 over the DM355.