
4-12
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part II. PowerPC Microprocessor Module
4.5.3.1 Executing Load/Store Instructions
When load or store instructions are dispatched, the LSU determines if all of the operands
are available. These operands include the following:
¥
Address register operands
¥
Source data register operands (for store instructions)
¥
Destination data registers (for load instructions)
¥
Destination address GPRs (for load/store with update instructions)
If all operands are available, the LSU takes the instruction and enables the sequencer to
issue a new instruction. Then, using a dedicated interface, the LSU notiÞes the integer unit
of the need to calculate the EA. All load/store instructions are executed and Þnished in
order. If no prior instructions are in the address queue, the load/store operation is issued to
the data cache when the instruction executes. Otherwise, if prior instructions remain whose
addresses have not been issued to the data cache, the instructionÕs address and data are
placed in their respective queues. For load/store with update instructions, the destination
address register is written back on the following clock cycle, regardless of the address
queueÕs state.
4.5.3.2 Serializing Load/Store Instructions
The following load/store instructions are not executed until all previous instructions have
Þnished.
¥
Load/store multiple instructionsÑlmw, stmw
¥
Memory synchronization instructionsÑlwarx, stwcx., sync
¥
String instructionsÑlswi, lswx, stswi, stswx
¥
Move to SPRs
The following load/store instructions must Þnish before more instructions can be issued.
¥
Load/store multiple instructionsÑlmw, stmw
¥
Memory synchronization instructionsÑlwarx, stwcx., sync
¥
String instructionsÑlswi, lswx, stswi, stswx
4.5.3.3 Store Accesses
Because the core supports the precise exception model, a new store instruction cannot
update the data cache until all prior instructions have Þnished without an exception. If a
store instruction follows a load instruction, a one-clock delay is inserted between the load
bus cycle termination and the store cycle issue.
4.5.3.4 Nonspeculative Load Instructions
Load instructions targeted at nonspeculative memory are identiÞed as nonspeculative one
clock cycle after the previous load/store bus cycle ends, only if all prior instructions have
Þnished without an exception.
Содержание MPC860 PowerQUICC
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