Instruction Execution Timing
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
9-3
Figure 9-4. Private Writeback Bus Load Timing
9.1.4
Fastest External Load (Data Cache Miss)
Figure 9-5
shows a sub instruction dependent on the value read by the load. It causes three bubbles in the
execution stream. Assuming SCCR[EBDF] = 00, the external clock (CLKOUT) is shifted 90
°
from the
internal clock (GCLK1).
lwz
r12,64 (SP)
sub
r3,r12,3
addic
r4,r14,1
Figure 9-5. External Load Timing
9.1.5
A Full Completion Queue
Figure 9-6
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
ori
xor
load
lwz
sub
and
xor
cror
ori
sub
and
cror
ori
load
sub
lwz
lwz
lwz
lwz
sub
lwz
cror
and
and
xor
xor
ori
GCLK1
E Data
Fetch
Decode
Read + Execute
Writeback
L Address Drive
L Data
Cache Address
Load Writeback
E Address
cror
lwz
sub
lwz
lwz
sub
addic
sub
sub
lwz
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
Summary of Contents for PowerQUICC MPC870
Page 98: ...MPC885 PowerQUICC Family Reference Manual Rev 2 I 4 Freescale Semiconductor ...
Page 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Page 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
Page 288: ...MPC885 PowerQUICC Family Reference Manual Rev 2 III 4 Freescale Semiconductor ...
Page 554: ...MPC885 PowerQUICC Family Reference Manual Rev 2 V 6 Freescale Semiconductor ...
Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Page 1336: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 16 Freescale Semiconductor ...
Page 1358: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 38 Freescale Semiconductor ...
Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...