Issues with Quartis...

Regarding the counting in your statemachine:

How are the signals in the if statement related to the statemachine clock?

Your described behaviour may suggest that at least RxReady is asynchronous

to clk16xt.

As for the memory:

I'm not sure how well it should transform automatically into a memory block,

but you constructed a global clear in the reset state.

Something the embedded memory blocks are incapable of.

Cheers, Roger