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DS90UB949-Q1: FPD-Link loss of lock vs SDI corruption

Harsh Rajoria
Prodigy 10 points

Part Number: DS90UB949-Q1

Hello, I intend to use the DS90UB949 IC for HDMI to FPD-Link III conversion which I understand has back-channel CRC checking. My question was - is this checking only on the control or the video as well? If there is a corruption in the video, do we lose the whole frame? I know that the SDI format will just lose a pixel or a few lines depending on how severe the corruption is so I just wanted to clarify this difference between SDI and FPD-Link III.

  • 0
    TI__Genius 11666 points

    Hi Harsh,

    The back-channel CRCs are only for data being sent over the back-channel, so they do not check video going over the forward channel. 

    Harsh Rajoria said:
    If there is a corruption in the video, do we lose the whole frame?

    It depends on what type of corruption you are talking about. Could you provide an example scenario?

    BR,

    Cameron

  • 0 in reply to Harsh Rajoria
    Prodigy 10 points
    There is supposedly a "BIST" mode which when activated will check for errors in the forward channel and pass it back to the back-channel CRC. Is my understanding correct? As for your latter question, there are two scenarios:
    1. When a brief lock-loss occurs mid-frame (say due to signal degradation, impedance mismatch, cable noise spike etc.), does the system abort the current frame entirely and wait for the next Frame Start, or does it deliver a partial/corrupted frame buffer to the SoC?
    2. If a frame start/end packet is corrupted or missed by the serializer, does the receiver drop the entire frame because it loses frame boundary sync, or does it recover at the next line?
  • 0 in reply to Harsh Rajoria
    TI__Genius 11666 points

    Hi Harsh,

    Harsh Rajoria said:
    When a brief lock-loss occurs mid-frame (say due to signal degradation, impedance mismatch, cable noise spike etc.), does the system abort the current frame entirely and wait for the next Frame Start, or does it deliver a partial/corrupted frame buffer to the SoC?

    With a loss of lock, the entire video path gets disrupted and the corresponding behavior on the display will depend on the deserializer being used. As for the activity on the FPD channel, when lock is lost, any video being transmitted while lock is low will also be lost. Once lock is regained, video will continue to be displayed. For most video signals, this will typically result in at least a full frame being lost due to the re-lock time and recovery time being about as long as it takes to transmit a full frame.

    Harsh Rajoria said:
    If a frame start/end packet is corrupted or missed by the serializer, does the receiver drop the entire frame because it loses frame boundary sync, or does it recover at the next line?

    I'm not quite sure I understand what you mean by frame start/end packet, I don't believe there is anything like this in the HDMI protocol. Our serializer will look at the incoming horizontal sync and vertical sync pulses as well as the incoming pixel clock to determine frame boundaries. If a video source does not output a sync pulse, the video will likely get corrupted, but the serdes should still continue to display so long as a valid pixel clock is being supplied to the SER. Things like this are heavily system dependent, so exact behavior is hard to predict without knowing the exact variables of the system.

    Harsh Rajoria said:
    There is supposedly a "BIST" mode which when activated will check for errors in the forward channel and pass it back to the back-channel CRC. Is my understanding correct?

    Yes, the BIST mode will check for errors of the signal coming from the SER; however, this does not apply to custom video going into the SER. The SER will generate a test pattern that the DES is expecting, and the DES will test for errors against what it is expecting to receive on the FPD RX.

    Best,

    Cameron