I've read the handbook description but this doesn't seem to be very comprehensive.
What I think I understand is (for Stratix III) that a reference is compared to the output of a 16 element delay chain. The tap position is adjusted until the output of the delay chain is in sync with the input (or as close as it can get). Once set then presumably given that the delay elements are of equal delay you can select a known phase assuming that the ref is within given frequency limits. The tap position is then used to drive delay elements in DQS blocks to delay read strobes by a known amount. Presumably this relies on close matching of the delay elements in the DQS blocks and the DLL. Have I understood this correctly or not? Cheers,