Core Complex Overview
PowerPC e500 Core Family Reference Manual, Rev. 1
Freescale Semiconductor
1-15
indicating strongly taken, weakly taken, weakly not taken, and strongly not taken. The BTB is used
not only to predict branches, but to detect branches during the fetch stage, offering an efficient way
to access instruction streams for branches predicted as taken.
In the e500, all branch instructions are assigned positions in the completion queue at dispatch.
Speculative instructions in branch target streams are allowed to execute and proceed through the
completion queue, although they can complete only after the branch prediction is resolved as
correct and after the branch instruction itself completes.
If a branch resolves as correct, instructions in the target stream are marked nonspeculative and are
allowed to complete. If the branch history bits in the BTB indicated weakly taken or weakly not
taken, the prediction is upgraded to strongly taken or strongly not taken.
If a branch resolves as incorrect, instructions in the target stream are flushed from the execution
pipeline, the branch history bits are updated in the BTB entry, and nonspeculative fetching begins
from the correct path.
Содержание PowerPC e500 Core
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