arm - ARM Cortex-A8 流水线是 13 级还是 14 级？

Question

如果您在 ARM presentations 中看到这个流行的 ARM Cortex-A8 流水线图.很明显，指令获取阶段需要 3 个周期，但第一个周期是有点折扣。但为什么？有什么想法吗？

谢谢...

Answer 1

来自 Cortex A8 上有些隐藏的论文:

The fetch pipeline begins with the F0 stage where a new virtual address is generated. This address can either be a branch target address provided by a branch prediction for a previous instruction, or if there is no prediction made this cycle, the next address will be calculated sequentially from the fetch address used in the previous cycle. Note that the F0 Fetch stage is not counted as an official stage in the 13 stage main integer pipeline. This is because ARM processor pipelines have always counted stages beginning with the Instruction Cache access as the first stage.