One of the major design goals of Niagara2 was to support
deterministic and repeatable behavior in functional mode for
system debug and test. The serial I/O interfaces which account
for 90% of the pins present challenges to that goal, but most
of the logic directly supports it through ratioed synchronous
clocking. In system debug mode, the repeatability issue is addressed
by buffering in the memory pathway to account for
maximum round-trip delays through the FBDIMM interfaces.
Design for manufacturing tests achieves determinism and tester
level cycle repeatability using a special mode described later.