SH7710 Datasheet, PDF (120/996 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 3 DSP Operating Unit
3.3 CPU Extended Instructions
3.3.1 Repeat Control Instructions
In DSP mode, a specific function is provided to execute repeat loops efficiently. By using this
function, loop programs can be executed without overhead caused by the compare and branch
instructions.
Examples of Repeat Loop Programs: Examples of repeat loop programs are shown below.
• Example 1: Repeat loop consisting of 4 or more instructions
LDRS RptStart
; Sets repeat start instruction address
to the RS register
LDRE RptStart +4
; Sets (repeat detection instruction
address + 4) to the RE register
SETRC #4
; Sets the number of repetitions (4) to
the RC[11:0] bits of the SR register
Instr0
; At least one instruction is required
from SETRC instruction to [Repeat start
instruction]
RptStart: instr1
; [Repeat start instruction]
... ...
;
... ...
;
RptDtct: instr(N-3)
; Three instruction prior to the repeat
end instruction is regarded as repeat
detection instruction
RptEnd2: instr(N-2)
;
RptEnd1: instr(N-1)
;
RptEnd: instrN
; [Repeat end instruction]
In the above program example, instructions from the RptStart address (instr1 instruction) to the
RptEnd address (instrN instruction) are repeated four times. These repeated instructions in the
program are called repeat loop. The start and end instructions of the repeat loop are called the
repeat start instruction and repeat end instruction, respectively. The CPU sequentially executes
instructions and starts repeat loop control if the CPU detects the completion of a specific
instruction. This specific instruction is called the repeat detection instruction. In a repeat loop
consisting of 4 or more instructions, an instruction three instructions prior to the repeat end
instruction is regarded as the repeat detection instruction. In a repeat loop consisting of 4 or more
instructions, the same instruction is regarded as the RptStart instruction and RptDtct instruction.
Rev. 2.00 Dec. 07, 2005 Page 78 of 950
REJ09B0079-0200