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Original question:

DS90UB935-Q1: Question about DS90UB935-Q1 and DS90UB962-Q1

DS90UB936-Q1: max latency time

Elec Cheng
Expert 7055 points
Part Number: DS90UB936-Q1

Hi Expert,

I see below e2e thread and have some question. For each port, there is a buffer and FIFO for two line data capacity. I see in the table that front porch, back porch and sync pulse. Aren't they for RGB signal? Why they are for VASE? How to get the PIXEL clock? 

I also think transmit a long packet also cost some time? Is it very little so you omit it? Thanks.

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/860039/faq-ds90ub953-q1-latency-of-ds90ub953-q1-and-ds90ub954-q1

BR,

Elec Cheng

  • 0
    TI__Guru** 103215 points

    Hello Elec,

    Horizontal blanking is not transferred in CSI-2, but the video will still have some line time which is defined by the effective Vtotal of the video and the frame rate. That line time is what you would use to calculate the latency. All you need to know for calculating this in the context of CSI-2 is the Vtotal and the frame rate - with that you have all the information you need to calculate the line time. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 7055 points

    Hi Casey,

    Casey McCrea said:
    Vtotal and the frame rate

    I don't really understand why Vtotal is needed. I suppose we need Htotal. Also, how do you get Pixel freq? 1280*800*1.2*60= 73MHz, not 83.46MHz. What does "Vertical refresh" mean? Thanks.

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Guru** 103215 points

    Elec,

    This is an example of a standard video timing. Vertical refresh is inverse of the line time (1/49.67kHz = 20.1us)

    This is also equal to the 1/(vtotal*fps) = 1/(828*60)

    The concept of PCLK frequency is less applicable in CSI-2 because the pixel rate can be asynchronous to the transmission rate (sent in bursts with dead time in-between). Instead it is best to use the Vtotal and FPS to calculate an effective line time which basically corresponds to how quickly the line buffer in the DES will fill up. Because the DES always buffers a full video line before sending

    Best Regards,

    Casey