10-4
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part II. PowerPC Microprocessor Module
10.1.5 A Full Completion Queue
Figure 10-6 shows stalls due to a full CQ. Here, the CQ is full from executing sub, addic,
and and. It takes one more bubble from the load writeback to allow further issue while the
CQ retires sub, addic, and and.
lwz r12,64
(SP)
sub
r5,r5,3
addic
r4,r14,1
and
r3,r4.r5
xor
r4,r3,r5
ori
r7,r8,1
Figure 10-6. Full Completion Queue Timing
10.1.6 Branch Instruction Handling
In Figure 10-7 the lwz instruction accesses internal memory with one wait state. The IQ and
parallel operation of the BPU allows the two bubbles caused by the bl issue and execution
to overlap the two bubbles caused by the load. Issuing bl causes a bubble because it does
no work.
lwz
r12,64 (SP)
sub
r3,r12,3
addic
r4,r14,1
bl
func
...
func:
mulli
r5,r3,3
addi
r4,3(r0)
xor
xor
lwz
lwz
sub
and
xor
addic
ori
sub
and
addic
xor
lwz
sub
lwz
lwz
lwz
lwz
lwz
sub
lwz
addic
addic
and
and
Bubble
GCLK1
E Data
Fetch
Decode
Read + Execute
Writeback
L Address Drive
L Data
Cache Address
Load Writeback
E Address
Bubble
Содержание MPC860 PowerQUICC
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