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TVP5158 Line Interleaved Mode

Michael Hallak-Stamler
Prodigy 205 points
Other Parts Discussed in Thread: TVP5158

I understand that the BT.656 super-frame that is build consists of video lines each of which has a unique identifier defining the source and line number. Also, I understand that the nature of the asynchronous inputs necessarily means that from time to time dummy lines with no video will be inserted. To this I have the following questions:

1. The TVP has to sense vertical sync for each of the four inputs separately. It seems to me then, that the line number that appears in the super-frame for one input can be radically different than the line number of the next line that represents a different input. That is, it is possible for two consecutive lines to appear from input A, B to have, say line number 25 for A and line number 286 for B. Is this so? If so, then the video input processor has to carefully build each of the four input fields from this information and that the asynchronous nature of the input are maintained, i.e. only lines are synchronized but not fields or frames.

2. Is it possible under any circumstances for video lines to be lost, say during the output of dummy lines?

Thank

Michael Stamler

 

 

  • 0
    TI__Genius 16810 points

    Michael,

    1.  Correct,  the fields of the 4 channels will not be synchronized.  The processor has to construct individual fields from the lines in the super-frame.

    2.  The TVP5158 will not drop lines as long as the TVP5158 output line rate is faster than the video input line rate.   The TVP5158 provides a faster output line rate by reducing horizontal blanking in the super-frame output.  If the input line rate is significantly increased above nominal, line drops can occur.   The output horizontal blanking interval used by the TVP5158 is programmable, providing some adjustment to tolerance of higher input line rates.

    What output format and video processor will you be using?

  • 0 in reply to Larry Taylor
    Prodigy 205 points

    Hi Larry,

     

    Thanks for your answer. We are using a FPGA to perform preprocessing and then passing to a DM365 via the VPFE port.

    Regards

    Michael

     

  • 0 in reply to Larry Taylor
    Prodigy 140 points

    Hi Larry,

    Larry Taylor said:
    2.  The TVP5158 will not drop lines as long as the TVP5158 output line rate is faster than the video input line rate.   The TVP5158 provides a faster output line rate by reducing horizontal blanking in the super-frame output.  If the input line rate is significantly increased above nominal, line drops can occur.   The output horizontal blanking interval used by the TVP5158 is programmable, providing some adjustment to tolerance of higher input line rates.

    What would cause a significant increase in input line rate?  Shouldn't it be pretty much constant from an analogue camera?

    Is there any trade-off with reducing the horizontal blanking in the super frame output?  i.e. What problems could occur if I make it too small?

    Horizontal blanking == EAV2SAV, right?  So to reduce it I need to use registers B8h and B9h?  Would using the automatic duration control with maximum tolerance (4%) suffice, or should I set it to manual and choose a suitably small duration by trial-and-error?

    Kind regards

    Ian