Nios II DDR SDRAM read latency

How many clocks does your loop take without the IORD() ?

How many does it take if you do the IORD() twice in each loop (with nothing in between)?

Or try using signaltap to trace the actual cycle.

I've a note that says most reads from SDRAM took 16 clocks, but some took 12.

Writes were more interesting: single writes took 2 clocks, but the third took much longer. I assume a two stage 'pipeline' of some sort.

DDR will only be worse than SDRAM.