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Concept
Analyse temporelle statique
Résumé
Static timing analysis (STA) is a simulation method of computing the expected timing of a synchronous digital circuit without requiring a simulation of the full circuit.
High-performance integrated circuits have traditionally been characterized by the clock frequency at which they operate. Measuring the ability of a circuit to operate at the specified speed requires an ability to measure, during the design process, its delay at numerous steps. Moreover, delay calculation must be incorporated into the inner loop of timing optimizers at various phases of design, such as logic synthesis, layout (placement and routing), and in in-place optimizations performed late in the design cycle. While such timing measurements can theoretically be performed using a rigorous circuit simulation, such an approach is liable to be too slow to be practical. Static timing analysis plays a vital role in facilitating the fast and reasonably accurate measurement of circuit timing. The speedup comes from the use of simplified timing models and by mostly ignoring logical interactions in circuits. This has become a mainstay of design over the last few decades.
One of the earliest descriptions of a static timing approach was based on the Program Evaluation and Review Technique (PERT), in 1966. More modern versions and algorithms appeared in the early 1980s.
In a synchronous digital system, data is supposed to move in lockstep, advancing one stage on each tick of the clock signal. This is enforced by synchronizing elements such as flip-flops or latches, which copy their input to their output when instructed to do so by the clock. Only two kinds of timing errors are possible in such a system:
A Max time violation, when a signal arrives too late, and misses the time when it should advance. These are more commonly known as setup violations/checks which actually are a subset of max time violations involving a cycle shift on synchronous paths.
A Min time violation, when an input signal changes too soon after the clock's active transition.
Source officielle
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