SH7713 Datasheet, PDF (119/904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 3 DSP Operating Unit
To control the repeat loop, the DSP extended control registers, such as the RE register and RS
register and the RC[11:0] and RF[1:0] bits of the SR register, are used. These registers can be
specified by the LDRE, LDRS, and SETRC instructions.
• Repeat end register (RE)
The RE register is specified by the LDRE instruction. The RE register specifies (repeat
detection instruction address +4). 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. A repeat loop consisting of three or less instructions is described later.
• Repeat start register (RS)
The RS register is specified by the LDRS instruction. In a repeat loop consisting of 4 or more
instructions, the RS register specifies the repeat start instruction address. In a repeat loop
consisting of three or less instructions, a specific address is specified in the RS. This is
described later.
• Repeat counter (RC[11:0] bits of the SR)
The repeat counter is specifies the number of repetitions by the SETRC instruction. During
repeat loop execution, the RC holds the remaining number of repetitions.
• Repeat flags (RF[1:0] bits of the SR)
The repeat flags are automatically specified according to the RS and RE register values during
SETRC instruction execution. The repeat flags store information on the number of instructions
included in the repeat loop. Normally, the user cannot modify the repeat flag values.
The CPU always executes instructions by comparing the RE register to program counter values.
Because the PC stores (the current instruction address +4), if the RE matches the PC during repeat
instruction detection execution, a repeat detection instruction can be detected. If a repeat detection
instruction is executed without branching and if RC[11:0] > 0, then repeat control is performed. 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.
Examples 2 to 4 show program examples of the repeat loop consisting of three instructions, two
instructions, and one instruction, respectively. In these examples, an instruction immediately prior
to the repeat start instruction is regarded as a repeat detection instruction. The RS register specifies
the specific value that indicates the number of repeat instructions.
Rev.1.50 Aug. 30, 2006 Page 79 of 860
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