AD9371 Framer lane FIFO read/write pointer delta has changed

Question

When we reinitialize our JESD interface using _jesdInit(), we see the Rx Framer status of 0x7e rather than 0x3e about 2% of the time, indicating that the "Framer lane FIFO read/write pointer delta has changed." I have seen a few other similar inquiries but have not seen a clear answer to those questions so I am posting this one. Also, I have looked over the JESD204B Debugging document but I don't see what is causing our problem. I would like to know: 1) What causes this error in the framer path, 2) Is this error clear-on-read or do we need to clear it another way, 3) Other questions submitted indicate that their link appears to be running fine when this error is indicated so what are the issues with continuing to use the link rather than clearing the error. BTW, the Xilinx JESD204B cores on the opposite side of the link do not show any errors. Any help would be appreciated. Thank you.

cpeters · Accepted Answer

Good timing. Our FPGA engineer has actually made some progress on this. We think we've been able to eliminate the 7E issue by a changing the timing of the write to MYKONOS_ADDR_SERIALIZER_SPECIAL. This is normally called in mykonos.c in the function MYKONOS_setupSerializers(). 
 
 CMB_SPIWriteByte(device->spiSettings, MYKONOS_ADDR_SERIALIZER_SPECIAL, 0x03); 
 
 We've changed that line to

CMB_SPIWriteByte(device->spiSettings, MYKONOS_ADDR_SERIALIZER_SPECIAL, 0); 
 
 Then we added the setting of MYKONOS_ADDR_SERIALIZER_SPECIAL to 0x03 to our "headless" code implementation right before "Step 15" from the users guide. Step 15 is "Send the SYSREF signal to bring up the JESD204B interface." 
 
 Using this approach we've not seen the 0x7E issue in 1000's of tuning iterations. 
 
 Also, we've setup a PRBS loopback test and observed that the 7E issue, when it occurs does not seem to impact data integrity. 
 
 We understand that updating Mykonos.c is not allowed by ADI, but since they could not seem to help, you gotta do what you gotta do.)

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AD9371 Framer lane FIFO read/write pointer delta has changed