The MPC8xx Core
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
3-11
Figure 3-5. LSU Functional Block Diagram
To execute multiple/string instructions and unaligned accesses, the LSU increments the EA to access all
necessary data. This allows the LSU to execute unaligned accesses without stalling the master instruction
pipeline.
3.6.3.1
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. Using a dedicated interface, the LSU notifies the integer unit of the need to calculate the EA.
All load/store instructions are executed and finished 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 instruction’s 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 queue’s state.
Integer
Unit
GPRs
32-Bit
Integer
Load Data
32-Bit
Address
Integer
Store Data
Integer
Data Queue
LOAD/STORE
CORE
32-Bit
32-Bit
D-Cache/D-MMU
Interface
Address
Queue
and
Increment
32-Bit
32-Bit
UNIT
Summary of Contents for PowerQUICC MPC870
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Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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