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What is the performance of the branch prediction logic ?

Applies to: ARM1136, ARM1176

Answer

There is dynamic and static branch prediction logic on the ARM11 cores to predict conditional direct branches (some indirect branches are also predicted using the Return Stack). The dynamic branch prediction logic keeps a running history of whether a branch was taken, the branch information/history is stored in the Branch Target Address Cache (BTAC). If the branch information is not contained in the BTAC, static branch prediction is used, whereby we assume the branch will be taken if the branch is a conditional backwards branch or not taken if the branch is a conditional forwards branch.

Using a combination of dynamic and branch prediction we can typically correctly predict whether the branch will be taken about 85% of the time. If the branch prediction fails, the core pipeline will need to be refilled and the current instruction pipeline flushed.

 

Article last edited on: 2008-09-09 15:47:51

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