All,As some of you may know, Randy & I have been working on getting reliable data transmission across the inter-chip connections on the BEE2. We managed to get that working reliably and have moved on to the next problem that has reared its ugly head.
Once we got back to the point of looking at spectra again, we soon noticed that we are occasionally getting spurs, on the odd harmonics of our clock freq +/- the input frequency. That is, if our input frequency is 51Mhz, we'll see a spike at 51MHz, 149MHz, 251MHz, 549MHz, and 651MHz. Our iBOB is using ADC_CLK which we have set to 800MHz, the iBOB provides the clock to the BEE2 usr_clk2x input.
Further investigation revealed that our two XAUI links (from the same iBOB) are getting out of sync. The eight samples from the ADC are transmitted to the BEE2 over XAUI... four samples on XAUI0 and the other four samples on XAUI1. Once they arrive at the BEE2, they are sometimes out of sync. Its hard to explain in an email, but if we look at the received sample values (in BRAMs) we can discern the sine wave, but with discontinuities as if the samples are scrambled. We have seen the sync & unsync condition come & go over periods of a half hour or so, so maybe there's some sort of clock drifting going on...?
We verified the unsync condition by generating various test patterns in the iBOB. If we transmit all 1's on one clock and all 0's on the next, the two are out of sync at the BEE2. If we transmit all A's, then all 5's, the two are generally in sync but we have seen it go out of sync, but not as often. We also transmitted a 32-bit counter value across the two XAUIs and have seen it go sync and unsync.
Has anyone ever experienced this? Or are there any suggestions? I attached a pdf of our iBOB sampler design. At the BEE2, we simply slice apart the incoming XAUI data and shove it in BRAMs.
Thanks in advance! Jason
i_GUPPi_SAMP_800_A_0.pdf
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