Cortex-A8 R2P2.pdf - ARM Information Center

Program Flow Prediction5.1 About program flow predictionThe processor contains program flow prediction hardware, also known as branchprediction. With program flow prediction disabled, all taken branches incur a 13-cyclepenalty. With program flow prediction enabled, all mispredicted branches incur a13-cycle penalty.To avoid this penalty, the branch prediction hardware operates at the front of theinstruction pipeline. The branch prediction hardware consists of:• a 512-entry 2-way set associative Branch Target Buffer (BTB)• a 4096-entry Global History Buffer (GHB)• an 8-entry return stack.An unpredicted branch executes in the same way as a branch that is predicted as nottaken. Incorrect or invalid prediction of the branch prediction or target address causesthe pipeline to flush, invalidating all of the following instructions.5-2 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E