Every crossing is also a timing path, but asynchronous crossings cannot be timed like ordinary paths. This topic explains how CDC intent is expressed with three generic constraint concepts — clock groups, false paths, and bounded datapath delay limits — what static timing analysis then checks and stops checking, and how constraint reviews keep the exceptions honest.
Lesson | After it you can... |
|---|---|
Say what STA checks across clocks and why a synchroniser needs a bounded setup with no logic. | |
Judge when declaring clocks asynchronous or paths false is justified and what evidence it needs. | |
Explain why Gray pointers and crossing buses need a datapath-only delay bound. | |
Review constraints against the crossing inventory and spot the typical mistakes. |
Because there is no fixed phase relationship for the analysis to check setup and hold against, so ordinary timing either fails spuriously or forces over-constraint. The crossing needs a synchroniser plus an explicit statement of intent instead.