Pipeline Execution of Instruction Types
5-14
Figure 5–13. Store Execution Block Diagram
Memory
E2
E3
Memory controller
Register file
E1
.D
Data
E2
Address
Functional
unit
When you perform a load and a store to the same memory location, these rules
apply (
i = cycle):
-
When a load is executed before a store, the old value is loaded and the
new value is stored.
i
LDW
i + 1
STW
-
When a store is executed before a load, the new value is stored and the
new value is loaded.
i
STW
i + 1
LDW
-
When the instructions are executed in parallel, the old value is loaded first
and then the new value is stored, but both occur in the same phase.
i
STW
i
||
LDW
There is additional explanation of why stores have zero delay slots in section
5.2.4.