SH7713 datasheet(121/904 Pages) RENESAS

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Section 3 DSP Operating Unit

Rev.1.50 Aug. 30, 2006 Page 81 of 860

REJ09B0288-0150

• Example 4: Repeat loop consisting of one instruction

LDRS RptStart +8

; Sets (repeat detection instruction

address + 8) 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

; If RE-RS==-4 during SETRC instruction

execution, the repeat loop is regarded

as one-instruction repeat.

RptDtct:

instr0

; An instruction prior to the Repeat

start instruction is regarded as a

repeat detection instruction.

RptStart:

RptEnd:

instr1

; [Repeat start instruction] ==

[Repeat end instruction]

In repeat loops consisting of three instructions, two instructions and one instruction, specific

addresses are specified in the RS register. RE – RS is calculated during SETRC instruction

execution, and the number of instructions included in the repeat loop is determined according to

the result. A value of 0, –2,and –4 in the result correspond to 3 instructions, two instructions, and

one instruction, respectively.

If repeat instruction execution is completed without branching and if RC[11:0]>0, an instruction

following the repeat detection instruction is regarded as a repeat start instruction and instruction

execution is repeated for the number of times corresponding to the recognized number of

instructions. If RC[11:0]

≥ 2 when the repeat end instruction is completed, the RC[11:0] is

decremented by 1 and then control is passed to the address specified by the RS register. If

RC[11:0] ==1(or 0) when the repeat end instruction is completed, the RC[11:0] is cleared to 0 and

then the control is passed to the next instruction following the repeat end instruction.

Note:

If RE – RS is a positive value, the CPU regards the repeat loop as a four-instruction repeat

loop. (In a repeat loop consisting of four or more instructions, RE – RS is always a

positive value. For details, refer to example 1 above.) If RE – RS is positive, or a value

other than 0, –2,and –4, correct operation cannot be guaranteed.

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