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Version 2.03
3.2.2 Data Cache Instructions
Data Cache Block Allocate X-form
Data Cache Block Touch
X-form
dcba RA,RB
[Category: Embedded]
dcbt
dcbt
RA,RB,TH [Category: Server]
TH,RA,RB [Category: Embedded]
31 /// RA RB 758 /
0 6 11 16 21 31
31 / TH RA RB 278 /
0 6 7 11 16 21 31
Let the effective address (EA) be the sum (RA|0)+(RB).
This instruction provides a hint that the program will
probably soon store into a portion of the block and the
contents of the rest of the block are not meaningful to
the program. The contents of the block are undefined
when the instruction completes. The hint is ignored if
the block is Caching Inhibited.
This instruction is treated as a Store (see Section 3.2)
except that the instruction is treated as a no-op if execution
of the instruction would cause the system data
storage error handler to be invoked.
Let the effective address (EA) be the sum (RA|0)+(RB).
The dcbt instruction provides a hint that describes a
block or data stream, or indicates the expected use
thereof. A hint that the program will probably soon load
from a given storage location is ignored if the location is
Caching Inhibited or, for the Server environment,
Guarded.
The only operation that is “caused” by the dcbt instruction
is the providing of the hint. The actions (if any)
taken by the processor in response to the hint are not
considered to be “caused by” or “associated with” the
dcbt instruction (e.g., dcbt is considered not to cause
any data accesses). No means are provided by which
software can synchronize these actions with the execution
of the instruction stream. For example, these
actions are not ordered by the memory barrier created
by a sync instruction.
The dcbt instruction may complete before the operation
it causes has been performed.
The nature of the hint depends, in part, on the value of
the TH field, as specified below. If TH≠0b1010 this
instruction is treated as a Load (see Section 3.2),
except that the system data storage error handler is not
invoked, and reference and change recording need
not be done.
Special Registers Altered:
None
Extended Mnemonics:
Extended mnemonics are provided for the Data Cache
Block Touch instruction so that it can be coded with the
TH value as the last operand for all categories.
Extended: Equivalent to:
dcbtct RA,RB,TH dcbt for TH values of 0b0000 -
0b0111;
other TH values are invalid.
dcbtds RA,RB,TH dcbt for TH values of 0b0000 or
0b1000 - 0b1010;
other TH values are invalid.
Chapter 3. Storage Control Instructions
353