SH7713 datasheet(126/904 Pages) RENESAS

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Section 3 DSP Operating Unit

Rev.1.50 Aug. 30, 2006 Page 86 of 860

REJ09B0288-0150

Execution of a repeat detection instruction must be completed without any branch so that the

CPU can recognize the repeat loop. Therefore, when the execution branches to an instruction

following the repeat detection instruction, the control will not be passed to a repeat start

instruction after executing a repeat end instruction because the repeat loop is not recognized by

the CPU. In this case, the RC[11:0] bits of the SR register will not be changed.

 If a conditional branch instruction is used in the repeat loop, an instruction before a repeat

detection instruction must be specified as a branch destination.

 If a subroutine call is used in the repeat loop, a delayed slot instruction of the subroutine

call instruction must be placed before a repeat detection instruction.

Here, a branch includes a return from an exception processing routine. If an exception whose

return address is placed in an instruction following the repeat detection instruction occurs, the

repeat control cannot be returned correctly. Accordingly, an exception acceptance is restricted

from the repeat detection instruction to the repeat end instruction. Exceptions such as interrupts

that can be retained by the CPU are retained. For exceptions that cannot be retained by the CPU, a

transition to an exception occurs but a program cannot be returned to the previous execution state

correctly. For details, refer to section 4, Exception Handling.

Notes: 1. If a TRAPA instruction is used as a repeat detection instruction, an instruction

following the repeat detection instruction is regarded as a return address. In this case, a

control cannot be returned to the repeat control correctly. In a TRAPA instruction, an

address of an instruction following the repeat detection address is regarded as return

address. Accordingly, to return to the repeat control correctly, place a return address

prior to the repeat detection instruction.

2. If a SLEEP instruction is placed following a repeat detection instruction, a transition to

the low-power consumption state or an exception acceptance such as interrupts can be

performed correctly. In this case, however, the repeat control cannot be returned

correctly. To return to the repeat control correctly, the SLEEP instruction must be

placed prior to the repeat detection instruction.

5. Branch from a repeat detection instruction

If a repeat detection instruction is a delayed slot instruction of a delayed branch instruction or a

branch instruction, a repeat loop can be acknowledged when a branch does not occur in a

branch instruction. If a branch occurs in a branch instruction, a repeat control is not performed

and a branch destination instruction is executed.

6. Program counter during repeat control

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