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SN65DSI83: Test pattern correctness

Abhimanyu Pandit
Prodigy 10 points
Part Number: SN65DSI83

Tool/software:

Hi,

I am trying to bring up a new LVDS display and I am using SN65DSI83 to convert MIPI-to-LVDS. I am able to generate the test pattern. One the TI engineer looked at the test pattern and said that the color bar is not consistent, meaning that the timing values provided by the panel vendor are not 100% correct. How can i confirm looking at the test pattern whether the pattern is correct or not? What should I look for in the pattern? I have another working display of different resolution, even there I see the exact same pattern. Please help in understanding the below pattern. Thanks.

regards,

Abhimanyu

  • 0
    TI__Genius 17890 points

    Hi Abhimanyu,

    Could you please check that the LVDS clock rates and timings are correct for the display panel you are working with. The panel vendor should provide the full resolution with horizontal and vertical total, active, blanking values, along with frame rate and LVDS clock rate tolerances. 

    You can see this E2E for what the test patterns should look like: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/486770/test-pattern-of-sn65dsi84

    From the image here it looks correct pattern, but it would still help to check with the display resolution. Have you also tested with DSI input?

    Best regards,
    Ikram

  • 0 in reply to Ikram Haque
    Prodigy 10 points

    Hi Ikram,

    Yes I have tested with the DSI input but 99% of the time there is no output on the display, a couple of times I've seen the output on the display but the colors are messed up. As you can see in the picture below I see color strips instead of black and green instead of white. I've checked several times with the display vendor they say the timing parameter they've provided is correct and it what they are using on the demo board (no mipi-lvds bridge)

    regards,

    Abhimanyu

  • 0 in reply to Abhimanyu Pandit
    TI__Genius 17890 points

    Hi Abhimanyu,

    Could you check the LVDS data format of the display? 

    The OLDI/LVDS single port (using 4 data lanes and 1 clock) have two mapping formats (VESA and JEIDA) which are listed in this app note as Figure 1 and 2:

    https://www.ti.com/lit/an/snla014a/snla014a.pdf




    It's possible that the display requires a different format than what you are using. Please change the output format by toggling the DSI83 register 0x18[0] bit. The DSI83 datasheet also lists them as Format 1 and Format 2.




    Also, could you share what the image is supposed to look like. Is the current image stable?

    Best regards,
    Ikram


  • 0 in reply to Ikram Haque
    Prodigy 10 points

    Hello Ikram,

    Below is the LVDS format given in the display datasheet and the expected display output

    I've tried both format 1 and format 2 but I am not getting any output. The display vendor says that if the test pattern is display then the timing parameters are correct. Also, I am able to run older display with this new PCB. I am really stuck here. Let me know if you need any more details.

    regards,

    Abhimanyu

  • 0 in reply to Abhimanyu Pandit
    TI__Genius 17890 points

    HI Abhimanyu,

    You mentioned you are not getting any output, did you mean the output is like the previous email out shared with come colors being incorrect?
    Or is it blank screen with both format outputs?

    Also, could you share the register dump of all the registers when it is running with MIPI DSI input. This would help to check any errors.

    This FAQ also has some guidance on checking the input: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/852871/faq-sn65dsi84-no-display-output-with-sn65dsi83-sn65dsi84-sn65dsi85


    Best regards,
    Ikram

  • 0 in reply to Ikram Haque
    Prodigy 10 points

    Hello Ikram,

    I am getting the correct output on the display with LVDS format 2. I was missing a macro in one the files, after setting it right display works right. However, it is working only from the bootloader, not from the kernel. So once the device goes to sleep and wakes up, the display is blank. I am using the same configurations in bootloader as well as kernel. I've checked the CSR settings are same in both the cases. What else should I check to debug this?

  • 0 in reply to Abhimanyu Pandit
    TI__Expert 7130 points

    Hi Abhimanyu,

    Abhimanyu Pandit said:
    I am getting the correct output on the display with LVDS format 2.

    Is this with DSI input or test pattern?

    Abhimanyu Pandit said:
    So once the device goes to sleep and wakes up, the display is blank

    Do you mean the SN65DSI83 goes to sleep? 

    Can you provide the script that you are using to initialize the SN65DSI83?

    BR,

    Esther