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AM3874: Problems background color suddenly is displayed

shigehiro tsuda
Mastermind 9490 points

Part Number: AM3874

Hi,

The following problems occur in our customers.

The XXX_UNDERFLOW_STAT bit of clkc_underflow Register on AM3874 is set to 1. 
At that time, a set background color by COMP_back_color_settings Register is displayed to a display connected to HDMI only for a moment. 

What kind of cause is thought about?

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Guru**** 393215 points
    Moving this to the proper forum.
  • 0
    TI__Guru**** 170625 points
    Hi Shigehiro,

    If the COMP is disabled, or the channel within the COMP driving a particular VENC is disabled, or all inputs to a channel driving particular VENC are disabled, the underflow condition occurs at the VENC. This underflow condition is due to data is not being driven out of the COMP fast enough to keep up with the VENC read rate. Underflow can also happen due to lack of sufficient memory bandwidth or improper VPDMA configuration for any of the input channel. When underflow condition happens, the background color programmed in the COMP module is sent for the underflowed pixels.

    The background color in RGB format (COMP_back_color_settings[29:0] BACK_CLR) is output to VENCs to be used if underflow occurs.

    Similar issues for other TI devices (like AM335x) are resolved with:
    - Issue disappears on configuring PR_OLD_COUNT field in the EMIF control register(OCP config) to value close to zero.
    - L3 level initiator priority control – keep VPSS/HDMI at higher priority

    processors.wiki.ti.com/.../DA8xx_LCDC_Linux_FB_FAQs
    processors.wiki.ti.com/.../Sitara_Linux_SDK_DSS_FIFO_Underflow

    Regards,
    Pavel