IBM PowerPC 604 User Manual page 272

- Misaligned load string operations require two cycles per register plus two
additional cycles.
- Misaligned store string operations take six cycles per register being stored
(although the final store may only take three cycles if it does not cross a word
boundary).
• For instructions with both a CR result and either a GPR or an FPR result, the cycle
count shown is for the GPR or FPR result. CR results from logical or bit field
instructions that execute in the SCIU and CR results from instructions that execute
in the FPU take one additional cycle.
• Integer multiplies that detect an early exit condition finish a cycle earlier than others.
For signed multiplies, if the top 15 bits of the RB operand are all the same it is an
early out condition. For unsigned multiplies, if the top 15 bits are all zeros it is an
early out condition.
• All instructions are fully pipelined except for divides and some integer multiplies.
6-46
The integer multiplier is a three-stage pipeline. Integer multiplies other
than
those
that can exit early (described in the previous bullet) stall for one cycle in the first
stage of the pipeline. Integer divide instructions iterate in stage two of the multiplier.
Special-pwpose register operations can execute in the MCIU in parallel with
multiplies and divides.
- The FPU unit is a three-stage pipeline. Floating-point divides iterate in the
floating-point pipeline. The floating-point unit also has some data-dependent
delays not shown inTable 6-2. If the rounder has a carry out, that is, 1.11...111
rounds to 2.00 ... 000, the FPU takes an additional cycle. If the final normalization
of the result requires a shift of more
than
63, the FPU takes an additional cycle.
Underflow and overflow take an additional cycle. Denormalization to zero takes
an additional cycle. Massive cancellation resulting in zero takes an additional
cycle.
Table 6-2. Instruction Execution Timing
Instruction
Unit Cycle (cycle)
Serlallzatlon
acid
SCIU 1
-
acldc
SCIU 1
-
aclde SCIU
1 Execute
acldl SCIU
1
-
acidic SCIU
1
-
acidic. SCIU
1
-
acid ls SCIU
1
-
acid me SCIU
1 Execute
acldze SCIU
1 Execute
and SCIU 1
-
PowerPC 604 RISC Microprocessor User's Manual