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Synchronizing 4 ADC cores on the FMCADC4

Question asked by EJK on Nov 11, 2015
Latest reply on Nov 17, 2015 by EJK



I am having problems getting all 4 ADC cores on the FMCADC4 synchronized.


For all of my tests, I fed a common signal to both AD9680 chips, and looked at the data using Chipscope.


Case 1:  No changes to the GitHub code.

Result:  2 times out of 6 all 4 waveforms were aligned.  Otherwise, the outputs of the the 2 ADCs were off by as much as 5 samples.


Case 2:  Made the following changes to the ad9680.c


ad9680_spi_write(slave_select, 0x120, 0x1C);  // NSHOT sysref

ad9680_spi_write(slave_select, 0x121, 0x002);  // ignore first 2


Result:  4 times out of 8 all 4 waveforms were aligned.


Case 3:  Made the following changes:

In ad_fmcadc4_ebz.c

jesd204b_st.sysref_always_enable = 1;

Added the following in ad9680.c

ad9680_spi_write(slave_select, 0x120, 0x1A);  // Continous sysref

Result:  Unrecognizable waveforms.

Could someone please tell me what I need to do in order to reliably synchronize all 4 waveforms?


Thank you.