SH7205 Datasheet, PDF (85/1904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7200 Series

Section 2 CPU
(6) Delayed Branch Instructions
With the exception of some instructions, unconditional branch instructions, etc., are executed as
delayed branch instructions. With a delayed branch instruction, the branch is taken after execution
of the instruction immediately following the delayed branch instruction. This reduces disturbance
of the pipeline control when a branch is taken.
In a delayed branch, the actual branch operation occurs after execution of the slot instruction.
However, instruction execution such as register updating excluding the actual branch operation, is
performed in the order of delayed branch instruction → delay slot instruction. For example, even
though the contents of the register holding the branch destination address are changed in the delay
slot, the branch destination address remains as the register contents prior to the change.
Table 2.3 Delayed Branch Instructions
SH-2A CPU
BRA
TRGET
ADD
R1,R0
Description
Executes the ADD before
branching to TRGET.
Example of Other CPU
ADD.W R1,R0
BRA
TRGET
(7) Unconditional Branch Instructions with No Delay Slot
The SH-2A additionally features unconditional branch instructions in which a delay slot
instruction is not executed. This eliminates unnecessary NOP instructions, and so reduces the code
size.
(8) Multiply/Multiply-and-Accumulate Operations
16-bit × 16-bit → 32-bit multiply operations are executed in one to two cycles. 16-bit × 16-bit +
64-bit → 64-bit multiply-and-accumulate operations are executed in two to three cycles. 32-bit ×
32-bit → 64-bit multiply and 32-bit × 32-bit + 64-bit → 64-bit multiply-and-accumulate
operations are executed in two to four cycles.
(9) T Bit
The T bit in the status register (SR) changes according to the result of the comparison. Whether a
conditional branch is taken or not taken depends upon the T bit condition (true/false). The number
of instructions that change the T bit is kept to a minimum to improve the processing speed.
Rev. 1.00 Mar. 25, 2008 Page 53 of 1868
REJ09B0372-0100