Chapter 10 quiz

Check yourself: Taming Complexity

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Q1 You black-box a sub-module and an assertion is proven. What can you conclude for the real design? Nothing. The assertion holds for the real design too, because the black box only added behaviours. The assertion holds only if the sub-module is also proven. The proof is vacuous.

Q2 Which reduction can hide a real bug and therefore needs a written argument? A cut point Black-boxing a module Reducing a FIFO depth parameter Adding a helper assertion that is proven

Q3 Why does cutting the "expired" signal of a large watchdog counter help? It makes the counter count faster. Expired can now occur on any cycle, so FSM behaviour after a timeout is reachable at small depth; the big counter leaves the cone. It removes the need for reset. It turns liveness into safety.

Q4 In assume-guarantee reasoning, what must be true about each assumption? It must be a cover. It must be proven as an assertion on the block that produces those signals. It must be removed before signoff. It must involve only clocks.

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