mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 188

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

Instruction Execution Timing
8.2.6 Branch Prediction
while:
mulli r3,r12,r4
addi r4,3(r0)
...
lwz
cmpi 0,r12,3
addic r6,r5,1
blt
...
In this example, the blt instruction is dependent on the cmpi instruction. Nevertheless, the
branch unit predicts the correct path and allows an overlap of its bubbles with those of lwz.
When the cmpi writes back, the branch unit reevaluates the decision and if correct
prediction occurs no more action is taken and execution continues fluently. The fetched
instructions on the predicted path are not allowed to execute before the condition is finally
resolved. Instead, they are stacked in the instruction prefetch queue.
FETCH
DECODE
READ + EXECUTE
WRITEBACK
L ADDRESS DRIVE
L DATA
LOAD WRITEBACK
BRANCH DECODE
BRANCH EXECUTE
BRANCH FINAL
DECISION
GCLK1
r12,64 (r2)
cr0,while
LWZ
Figure 8-8. Example of Branch Prediction
Freescale Semiconductor, Inc.
For More Information On This Product,
LWZ
CMPI
MPC823 REFERENCE MANUAL
LWZ
Go to: www.freescale.com
LWZ
ADDIC
BUBBLE
BLT
BUBBLE
LWZ
BLT
CMPI
LWZ
BUBBLE
BLT
CMPI
ADDIC
CMP
MULLI
BLT
ADDIC
MULLI
ADD
ADDI
MOTOROLA
MULLI