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Bit-exact DM365 LCD output

Yulin
Expert 1625 points

Hi there,

I am debugging a display issue on DM365.
There is a LVDS TX and RX between DM365 and LCD module.
The VENC builtin color bar SEEMs fine but YUV422 video is wrong.
The YUV422 video seems to be saturated or bit-shifted.

I try to output 0x8000 in OSD layer with all VIDEO layers off and blending attribute disabled
in an apptempt to obtain 0x8000 on the LCD bus but LA shows 0x7000.

So my questions are:
1. How to obtain a LCD output same to the frame buffer?
2. VCLKP bit in VIOCTL has no effect. What else is required to make it effective ?

Thanks in advance.

 

  • 0
    TI__Mastermind 43875 points

    Yulin,

    There are a number of things that may be wrong.

    The first potential issue  is connectivity to the LVDS transmitter. Depending on your LCD there are 2 common ways of wiring the data bits. Please have a look at the following page for more information on the 2 formats used for 24 bit LCDs.

    http://processors.wiki.ti.com/index.php/LCD_connectivity#Connection_to_LVDS_LCDs

    Many LCD panels have a control bit which allows selection between the 2 formats.

    The reason a color bar would look fine even if the wrong format is used is that a color bar is constructed by making each color channel either completely on or completely off. This effectively means that the bit positions for each color can be mixed up and you can't see the resultant error. The best pattern to see these types of connectivity issues are color ramps, shading each color from completely off (black) up to fully on for each color (3 different ramps, one for each of red, green and blue)

    The next issue could be the color space converter configuration.

    BR,

    Steve

  • 0 in reply to Steve Clynes
    Expert 1625 points

    Steve,

    Yes, I am trying to output DC (0x8000 in RGB565 OSD layer) but the bus signal is 0x7000 before the ramp test.

    So, how to configure the DM365 VPBE for a bit-exact ramp test ?

    BR,

    Yulin

  • 0 in reply to Yulin
    TI__Mastermind 43875 points

    Yulin,

    I am not a software expert so cannot help too much with this.

    Basically, though, you should used /dev/fb to create a frame buffer then simply fill this frame buffer with your ramp data.

    There should be examples in the internet and possibly in the SDK showing how to set a simple frame buffer display in various formats.

    If you can't find anything then I would start a new forum thread asking how display a simple frame buffer image and someone more familiar on the software side should be able to help.

    BR,

    Steve