
4-24
G2 PowerPC Core Reference Manual
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MOTOROLA
Cache Control Instructions
coding these instructions is provided in Chapter 3, “Addressing Modes and Instruction Set
Summary,” and Chapter 10, “Instruction Set,” in the
Programming Environments Manual
.
4.8.1
Data Cache Block Invalidate (dcbi) Instruction
If the block containing the byte addressed by the EA is in the data cache, the cache block
is invalidated regardless of whether the block is in the exclusive or modified state. If
HID0[ABE] is set on a G2 core when a
dcbi
instruction is executed, the G2 core will
perform an address-only bus transaction. The
dcbi
instruction can only be executed when
the G2 core is in the supervisor state.
4.8.2
Data Cache Block Touch (dcbt) Instruction
This instruction provides a method for improving performance through the use of
software-initiated prefetch hints. The G2 core performs the fetch when the address hits in
the TLB or BAT registers, and when it is a permitted load access from the addressed page.
The operation is treated similarly to a byte load operation with respect to coherency.
If the address translation does not hit in the TLB or BAT mechanism, or if it does not have
load access permission, the instruction is treated as a no-op.
If the cache is locked or disabled, or if the access is to a page that is marked as guarded, the
dcbt
instruction is treated as a no-op.
If the access is directed to a write-through or caching-inhibited page, the instruction is
treated as a no-op.
The
dcbt
instruction never affects the referenced or changed bits in the hashed page table.
A successful
dcbt
instruction affects the state of the TLB and cache LRU bits as defined by
the LRU algorithm.
The touch load buffer will be marked invalid if the contents of the touch buffer have been
moved to the cache, if any data cache management instruction has been executed, if a
dcbz
instruction is executed that matches the address of the cache block in the touch buffer, or if
another
dcbt
instruction is executed.
4.8.3
Data Cache Block Touch for Store (dcbtst) Instruction
The
dcbtst
instruction, like the data cache block touch instruction (
dcbt
), allows software
to prefetch a cache block in anticipation of a store operation (read-with-intent-to-modify).
4.8.4
Data Cache Block Clear to Zero (dcbz) Instruction
If the block containing the byte addressed by the EA is in the data cache, all bytes are
cleared.
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