AD9371 Deframer FIFO depth adjust

Hi

On our customized board, we got the deframer fifo depth.
The FIFO depth is indicated the 30, 31, 32.

I think it is not good because it is FIFO depth boundary.

We changed the LMFC offset value on initdata.c however deframer fifo depth was not changed.

* LMFC = 0 : FIFO depth 30,31,32
* LMFC = 20 : FIFO depth 30,31,32

We want to know how to adjust the deframer fifo dpeth.

  • 0
    •  Analog Employees 
    on Nov 11, 2021 1:39 PM

    Are you facing any performance issues? If the FIFO depth varies by 1 or 2 samples with every boot up, it should not affect. Hope you are not changing the LMFC offset in runtime as that might give sysref alignment error.  You need to initialize the board with the new LMFC offset value.

  • I think the FIFO is 32.
    It is needed to changing for deterministic latency.

  • +1
    •  Analog Employees 
    on Nov 16, 2021 4:03 AM in reply to Toshihiro

    The FIFO depth of 32 looks good since the FIFO depth is 127 and the value is not close to both the boundaries.. 

    From UG:

    When establishing a JESD204B link, it is desirable that the data arriving to the deframer does not arrive very close to an LMFC boundary. If this does happen, the deterministic latency can vary from system to system if the data on one system arrives just before an LMFC event, and arrives on another system just after an LMFC event. If this happens, there is an LMFC period difference in the latency between the systems. Furthermore, the architecture in the device does not support a very small delay through the FIFO, and data corruption occurs if the delay is too small. Therefore, it is important that the FIFO depth be checked after the link is established, and the link is adjusted to achieve a FIFO depth that is close to the medium depth.

  • Sorry, we misunderstood about the FIFO depth.

    Could you please tell me just for my reference how does the fifo depth change?

  • 0
    •  Analog Employees 
    on Nov 16, 2021 4:29 AM in reply to Toshihiro

    The FIFO depth depends on the LMFC offset parameter. If you increase the LMFC offset by 1, then the FIFO depth can either increase by 1 or decrease by 1. So in this way, if you keep on keep on varying the LMFC offset value, then you will be able to achieve a FIFO depth that is in the medium depth value.