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AM335x enabling LCD screen cost system memory bandwidth?

Cao Yiling
Intellectual 400 points

Hi, I have a 800x480 screen, will enabling this cost much memory bandwidth? as 60Hz * 800 * 480 * 24bit = 65.9MB/s

I have tested memory bandwidth on this board is very limited 200-300MB/s (partly because max 16bit ram bandwidth).

Will this reduce system memory bandwidth for other processors? Just want to confirm my understanding.

  • 0
    TI__Guru**** 393215 points
    Hi Cao,
     
    Basically speaking your logic is right. However there are a lot of factors to take into consideration, like processor caches, memory type and size, software etc. If you need to evaluate there is a BeagleBone LCD7 Cape, which has a 800x480 resolution. Only difference from your rquirement is that the cape uses RGB565 format (16-bit RGB). It can be directly connected to a Beaglebone or Beaglebone Black and you can evaluate performance.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 400 points

    Thanks for your reply, I do have my own, custom built hardware can evaluate with. and it is 24bit. And I do know that I can disable my lcd with kernel. I am on my course to trying to optimize my system performance.

    Do you suggest to lower pixel clock, I.E. lowering 60Hz refresh rate to 50 or 40Hz? Do you think I will get performance increase? 

  • 0 in reply to Cao Yiling
    TI__Guru**** 393215 points
    I understand. I am not a software expert, but since the frame buffer is located in the external DDR, any action you take, like lowering the refresh rate or switching to 16-bit mode (though this may be hard as the color arrangement is different) will relax the LCD payload on the EMIF.