Several techniques have been proposed to reduce the number of pipeline stages.
We categorize them into two types based on their design philosophy: stage merging and stage bypassing.
Stage merging combines multiple stages of the traditional design into a single stage by using faster components or through speculation.
Faster components: allows the merging of VA and SA, LT and ST into the same stage
Speculation: With it, a flit ignores the dependence between various steps and speculatively（预测） executes multiple steps in parallel . If speculation fails, which rarely happens, the router needs to roll back and reexecute the steps sequentially.
Stage bypassing skips pipeline stages in intermediate routers when there is no load ahead or by setting up downstream routers before a flit arrives.
for example, ST and LT are merged.
Multiple intermediate routers are bypassed when there is no contentions in an advanced design SMART NOC.
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