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Developer’s Manual March, 2003 5-3
Intel
®
80200 Processor based on Intel
®
XScale
™
Microarchitecture
Branch Target Buffer
5.2 BTB Control
5.2.1 Disabling/Enabling
The BTB is always disabled out of Reset. Software can enable the BTB through a bit in a
coprocessor register (see Section 7.2.2).
Before enabling or disabling the BTB, software must invalidate it (described in the following
section). This action ensures correct operation in case stale data is in the BTB. Software should not
place any branch instruction between the code that invalidates the BTB and the code that
enables/disables it.
5.2.2 Invalidation
There are four ways the contents of the BTB can be invalidated.
1. Reset
2. Software can directly invalidate the BTB via a CP15, register 7 function. Refer to
Section 7.2.8, “Register 7: Cache Functions” on page 7-11.
3. The BTB is invalidated when the Process ID Register is written.
4. The BTB is invalidated when the instruction cache is invalidated via CP15, register 7
functions.