Pipeline Operation: Fetch Packets With Different Numbers Of Execute Packets - Texas Instruments TMS320C6000 Series Reference Manual

Figure 6–26. Pipeline Operation: Fetch Packets With Different Numbers of Execute
Packets
Fetch Execute
packet packet
(FP) (EP) 1
n k
PG
n k+1
n k+2
n+1 k+3
n+2 k+4
n+3 k+5
n+4 k+6
n+5 k+7
n+6 k+8
Clock cycle
2 3 4 5 6
É É
PS PW PR DP DC
É É É É É É É
DP
É É É
PG PS PW PR
PG PS PW Pipeline
PG PS
PG
In Figure 6–26, fetch packet n, which contains three execute packets, is
shown followed by six fetch packets (n + 1 through n + 6), each with one
execute packet (containing eight parallel instructions). The first fetch packet
(n) goes through the program fetch phases during cycles 1–4. During these
cycles, a program fetch phase is started for each of the fetch packets that
follow.
In cycle 5, the program dispatch (DP) phase, the CPU scans the p -bits and de-
tects that there are three execute packets (k through k + 2) in fetch packet n.
This forces the pipeline to stall, which allows the DP phase to start for execute
packets k + 1 and k + 2 in cycles 6 and 7. Once execute packet k + 2 is ready
to move on to the DC phase (cycle 8), the pipeline stall is released.
The fetch packets n + 1 through n + 4 were all stalled so the CPU could have
time to perform the DP phase for each of the three execute packets (k through
k + 2) in fetch packet n. Fetch packet n + 5 was also stalled in cycles 6 and 7:
it was not allowed to enter the PG phase until after the pipeline stall was
released in cycle 8. The pipeline continues operation as shown with fetch
packets n + 5 and n + 6 until another fetch packet containing multiple execu-
tion packets enters the DP phase, or an interrupt occurs.
7 8 9 10
E1 E2 E3 E4
DC E1 E2 E3
DP DC E1 E2
DP DC E1
PR DP DC
stall PW PR DP
PS PW PR
PG PS PW
PG PS
Performance Considerations
11 12 13 14 15
E5 E6 E7 E8 E9
E4 E5 E6 E7 E8
E3 E4 E5 E6 E7
E2 E3 E4 E5 E6
E1 E2 E3 E4 E5
DC E1 E2 E3 E4
DP DC E1 E2 E3
PR DP DC E1 E2
PW PR DP DC E1
TMS320C67x Pipeline
16 17
E10
E9 E10
E8 E9
E7 E8
E6 E7
E5 E6
E4 E5
E3 E4
E2 E3
6-53