Ratioed synchronous clocks have a number of other advan-
tages: FIFO designs are simpli
fi
ed; timing analysis is more ro-
bust since there are no false paths in this scheme; and functional
test vector generation becomes much easier. Sync-pulse-based
domain crossing for the generic case in Niagara2 is illustrated
in Fig. 13. All measurements are with respect to a starting point
at time 0, or
, where Fast Clock (FCLK), Slow Clock
(SCLK), and the reference clock have their rising edges aligned.
The
enable flop
always operates on the rising edge of the faster
clock domain, and the pulse remains active for exactly one fast
clock cycle. Also, data transfer is allowed every slow clock cycle
thus achieving maximum communication throughput. To suc-
cessfully use sync pulses, the following must be true: