Motorola MPC823e

Instruction Execution Timing
MOTOROLA MPC823e REFERENCE MANUAL 8-7
INSTRUCTION EXECUTION
8
TIMING
8.2.3 Fastest External Load (Data Cache Miss)
lwz r12,64 (SP)
sub r3,r12,3
addic r4,r14,1
The sub instruction is dependent on the value read by the load. It causes three bubbles in
the instruction execution stream. The external clock is shifted 90 ° relative to the internal
clock.
Figure 8-5. Example of an External Load
SUB
LWZ
LWZ SUB ADDIC
SUB
SUBLWZ BUBBLE
LWZ
LWZ
LWZ
LWZ
LWZ
LWZ
GCLK1
E DATA
FETCH
DECODE
READ + EXECUTE
WRITEBACK
L ADDRESS DRIVE
L DATA
CACHE ADDRESS
LOAD WRITEBACK
E ADDRESS
BUBBLE BUBBLE BUBBLE