基于跳跃访问控制的低功耗分支目标缓冲器设计

传统的分支目标缓冲器(BTB)每个取指周期都要进行访问,由于程序中的分支指令只占总指令数的20%左右,使得大约80%的BTB访问都是无效的.为此,利用程序控制流中分支指令间距固定的特性,提出一种对性能影响极小的BTB跳跃访问算法.在BTB中存储分支指令到运行路径中下一条分支指令的距离,BTB命中后,根据相应的分支距离来关闭当前分支指令与下一条分支指令之间的BTB访问,以有效地提高访问效率并降低动态功耗.该算法在嵌入式处理器中实现时只控制预测跳转分支指令的BTB跳跃访问,减少了硬件资源的开销.在硬件模型上进行模拟和综合后的结果表明,在128分支项的BTB中,采用文中算法可以降低72%的动态功耗,而性能损失仅为0.013%.

Low Power Branch Target Buffer Design Based on Hopping Access

The traditional branch target buffer(BTB)has to be always accessed during instruction fetch stage.Since the branch instructions account for about 20% of the total executed instructions,at least 80% of the BTB accesses are redundant.Considering the characteristic of the fixed distance of branch instructions,we proposed a hopping access(HA)algorithm,by which we reduced the accesses to the BTB to achieve a significant dynamic energy reduction while maintaining the performance.By performing HA algorithm the bra...