Renesas SH7641 - Manual (Page 174)

Section 3 DSP Operation
Rev. 4.00 Sep. 14, 2005 Page 124 of 982
REJ09B0023-0400
3.2 DSP Addressing
3.2.1 DSP Repeat Control
This LSI prepares a special control mechanism for efficient repeat loop control. An instruction
SETRC sets the repeat times into the repeat counter RC (12 bits), and an execution mode in which
a program loop executes repetitively until RC is equal to 1. After completion of the repeat
instructions, the RC value becomes 0.
Repeat start address register RS keeps the start address of a repeat loop. Repeat end register RE
keeps the repeat end address. (There are some exceptions. See note, Actual Implementation
Options.) Repeat counter RC keeps the number of repeat times. In order to perform loop control,
the following steps are required.
Step 1) Set loop start address into RS
Step 2) Set loop end address into RE
Step 3) Set repeat counter into RC
Step 4) Start repeat control
To do steps 1 and 2, use the following instructions:
LDRS @(disp,PC)
LDRE @(disp,PC)
For steps 3 and 4, use the SETRC instruction. An operand of SETRC is an immediate value or one
of the general-purpose registers that will specify the repeat times.
SETRC #imm; #imm->RC, enable repeat control
SETRC Rm; Rm->RC, enable repeat control