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MPC603e & EC603e RISC Microprocessors User's Manual
MOTOROLA
Simplified mnemonics are provided for the
mftb
instruction so it can be coded with the
TBR name as part of the mnemonic rather than requiring it to be coded as an operand. The
mftb
instruction serves as both a basic and simplified mnemonic. Assemblers recognize an
mftb
mnemonic with two operands as the basic form, and an
mftb
mnemonic with one
operand as the simplified form. Simplified mnemonics are also provided for Move from
Time Base Upper (
mftbu
), which is a variant of the
mftb
instruction rather than of
mfspr
.
The 603e ignores the extended opcode differences between
mftb
and
mfspr
by ignoring bit
25 of both instructions and treating them both identically. For more information refer to
Appendix F, “Simplified Mnemonics,” in
The Programming Environments Manual
.
2.3.5.2 Memory Synchronization Instructions—VEA
Memory synchronization instructions control the order in which memory operations are
completed with respect to asynchronous events, and the order in which memory operations
are seen by other processors or memory access mechanisms. See Chapter 3, “Instruction
and Data Cache Operation,” for additional information about these instructions and about
related aspects of memory synchronization.
Implementation Notes—
The following describes how the 603e handles memory
synchronization in the VEA.
The Instruction Synchronize (
isync
) instruction causes the 603e to discard all
prefetched instructions, wait for any preceding instructions to complete, and then
branch to the next sequential instruction (which has the effect of clearing the
pipeline behind the
isync
instruction).
The Enforce In-Order Execution of I/O (
eieio
) instruction is used to ensure memory
reordering of noncacheable memory access. Since the 603e does not reorder
noncacheable memory accesses, the
eieio
instruction is treated as a no-op.
Table 2-31 lists the VEA memory synchronization instructions for the 603e.
Table 2-32. Move from Time Base Instruction
Name
Mnemonic
Operand Syntax
Move from Time Base
mftb
r
D
,
TBR
Table 2-33. Memory Synchronization Instructions—VEA
Name
Mnemonic
Operand Syntax
Enforce In-Order Execution of I/O
eieio
—
Instruction Synchronize
isync
—