2-54
MPC7400 RISC Microprocessor Users Manual
Instruction Set Summary
2.3.4.3.8 Integer Load and Store String Instructions
The integer load and store string instructions allow movement of data from memory to
registers or from registers to memory without concern for alignment. These instructions can
be used for a short move between arbitrary memory locations or to initiate a long move
between misaligned memory Telds. However, in some implementations, these instructions
are likely to have greater latency and take longer to execute, perhaps much longer, than a
sequence of individual load or store instructions that produce the same results. Table 2-34
summarizes the integer load and store string instructions.
In the MPC7400 implementation operating with little-endian byte order, execution of a load
or string instruction will take an alignment exception.
Load string and store string instructions can involve operands that are not word-aligned.
Implementation Note
The following describes the MPC7400 implementation of
load/store string instructions:
¥
For load/store string operations, the hardware does not combine register values to
reduce the number of discrete accesses. However, if store gathering is enabled and
the accesses fall under the criteria for store gathering the stores can be combined to
enhance performance. At a minimum, additional cache access cycles are required.
2.3.4.3.9 Floating-Point Load and Store Address Generation
Floating-point load and store operations generate effective addresses using the register
indirect with immediate index addressing mode and register indirect with index addressing
mode. Floating-point loads and stores are not supported for direct-store accesses. The use
of oating-point loads and stores for direct-store access results in an alignment exception.
There are two forms of the oating-point load instructionsingle-precision and
double-precision operand formats. Because the FPRs support only the oating-point
double-precision format, single-precision oating-point load instructions convert
single-precision data to double-precision format before loading an operand into an FPR.
Table 2-33. Integer Load and Store Multiple Instructions
Name
Mnemonic
Syntax
Load Multiple Word
lmw
r
D
,d(r
A
)
Store Multiple Word
stmw
r
S
,d(r
A
)
Table 2-34. Integer Load and Store String Instructions
Name
Mnemonic
Syntax
Load String Word Immediate
lswi
r
D
,r
A
,
NB
Load String Word Indexed
lswx
r
D
,r
A
,r
B
Store String Word Immediate
stswi
r
S
,r
A
,
NB
Store String Word Indexed
stswx
r
S
,r
A
,r
B