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AFE7950: Expected latency of TI JESD204C IP with AFE7950

David Caruth
Prodigy 60 points
Part Number: AFE7950


Tool/software:

Hello,

I'm seeing a latency of ~2us between data going into the tx_lane_data port of the TI JESD204C IP and signal coming out of the DAC.  The DAC freq is 3GHz and the FPGA clock is 375MHz.  The LMFS of the IP is 8821 and both links of the AFE7950 are set to 4421 with E=3 (sysref freq = (375/192) MHz).  I see RBD values anywhere from 18 to 32 reported by Latte and the links come up successfully.  Any idea what could be causing such a large latency?  The TI JESD204C IP was set for E=1, but I don't think this could account for 2us.

Thanks,

Dave

  • 0
    TI__Expert 5065 points

    Hi David,

    Are you using the latest version of the TI JESD204C IP 1.12? I believe we have seen this issue in a previous version of the IP.

    It has been fixed in the latest versions could you please give the newest version a try if you are not using it?

    Best,

    Camilo

  • 0
    Prodigy 60 points

    Hi Camilo,

    Thanks for your reply.  I am using 1.11 because the Vivado project is 2022.2.  I think I read somewhere that 1.12 is for Vivado 2023.  Can you tell me which version I should use?  2023.1?  2023.2?

    Also, I did a back-to-back simulation of the 1.11 TX and RX IP in Vivado 2022.2, and the total latency was about 500ns, so I think a majority of the latency is coming from the AFE7950.  I'm only using an interpolation of 4, so I wouldn't expect the digital filter to have that much delay.

    Thanks!

    Dave 

  • 0 in reply to David Caruth
    TI__Mastermind 18351 points

    Hi David,

    The TI IP has been updated such that version 1.12 of the TI IP contains two cores, one for vivado version 2019.x to 2021.x and the other for 2022.x and newer. In your initial post you mentioned an E value of both '1' and '3', so i wanted to check if this was a mistake or is the setting different on the AFE and FPGA. It is recommended to have the same value set on both the AFE and FPGA side, so if they are different I would recommend making it so that they are equal. 

    Can you share how you are measuring the latency when you are seeing the 2us measurement? 

    Regards,

    David Chaparro