Sun Microsystems UltraSPARC-I - Control Transfer Instructions

Sun Microelectronics
287
17. Grouping Rules and Stalls
17.6 Control Transfer Instructions
One Control Transfer Instruction (CTI) can be dispatched per group. The follow-
ing control transfer instructions are not single group instructions: CALL, BPcc,
Bicc, FB(P)fcc, BPr, and JMPL. CALL and JMPL are always dispatched as the oldest
instruction in the group; that is, a group break is forced before dispatching these
instructions.
DONE, RETRY, and the second instruction of a delayed control transfer instruction
(DCTI) couple flush the pipe when they reach the W Stage, effectively inserting
nine bubbles into the pipe. The pipeline is flushed even if the second DCTI is an-
nulled.
17.6.1 Control Transfer Dependencies
UltraSPARC can group instructions following a control transfer with the control
transfer instruction. Instructions following the delay slot come from the predicted
instruction stream. For example, if a branch is predicted taken:
If the branch is predicted not taken:
FCMPLE16 → i6 GECN
1
N
2
N
3
W
FMOVr i5 GECN
1
N
2
N
3
W
setcc
GECN
1
N
2
N
3
W
BPcc GECN
1
N
2
N
3
W
FADD (delay slot) GECN
1
N
2
N
3
W
FMUL (branch target) GECN
1
N
2
N
3
W
setcc
GECN
1
N
2
N
3
W
BPcc GECN
1
N
2
N
3
W
FADD (delay slot) GECN
1
N
2
N
3
W
FDIV (sequential) GECN
1
N
2
N
3
W
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com