ZCU216 ADC/DAC Loopback Issue

[eldrick]

Hello,

Currently working on bringing up a ZCU216 board. I am able to boot the example design provided on the early access site (ZCU216 MTS).
I am using the XM655 breakout to test RX/TX loopback.

I notice that when I have a DAC and ADC channel connected together directly (via Carlisle SMAs and a F-F SMA adapter), the tile that contains that channel fails to come up - both the CLI provided in the design says that the tile is not ready, and looking at ILAs show that the AXI Stream is inactive. If I use the on-board baluns, I do not seem to run into this issue.

What could be the cause of this issue and what are some workarounds if I wanted to do a channel-to-channel loopback with the XM655?

The image below is an example CLI output when I connected ADC 224_0 and DAC 228_0 together.
Addititionally, will usually get the following error message after the "Tile: 0 NOT ready" line:

metal: error:      ADC 0 timed out at state 12 in XRFdc_WaitForRestartClr

[klumsde]

Step 12 indicates that it is stuck in ADC calibration. 

This could be because you are not receiving a signal at the input of this tile or perhaps there is signal energy over the KFS/N offset spur location. K being 1-4, N being 4 here 

[eldrick]

I am only able to see the ADC Tile transition to the ready state when the ADC is completely disconnected - this holds for the ZCU216 MTS example design as well - so it seems counter-intuitive that the cause is the lack of an input signal to the tile.
Could you elaborate?