every 4 DR cycles is lost at the point of l2clk–drl2clk
crossing after traversing 24 mm on chip.
c) Placement of the pulses to enable data transfers needs
to meet setup and hold constraints for all conditions of
PVT. This involves creating timing budgets that are used
to drive the static timing analysis (STA) tools, as well as
confirm design points.
In Niagara2, all conditions are satisfied by the generation
and distribution of sync pulses as outlined in Fig. 14. The align
detection block generates an aligned pulse deterministically
using the fact that the reference and CMP clocks are phase
aligned at the PLL due to local feedback. This aligned_A signal
is effectively the output of a digital phase detector, its periodicity
reflecting the common base period of the reference clock.
Aligned_A is then used to track the CMP tree latency using
delayed clocking to arrive at the Clock Control Unit (CCU)
boundary as Aligned_B. Thus, Aligned_A is synchronous to
cmp_pll_clk whereas Algined_B is synchronous to l2clk no
matter what the balanced CMP latency. This is a cheaper
alternative than having the PLL reference clock being sent
out side by side along with the CMP clock. Aligned_A has
one other function of generating a synchronous reset for the