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Section 2 CPU
Rev. 4.00 Sep. 14, 2005 Page 81 of 982
REJ09B0023-0400
2.6 DSP Extended-Function Instructions
2.6.1 Introduction
The newly added instructions are classified into the following three groups:
1. Additional system control instructions for the CPU unit
2. DSP unit memory-register single and double data transfer
3. DSP unit parallel processing
Group 1 instructions are provided to support loop control and data transfer between CPU core
registers or memory and new control registers added to the CPU core. DSP operations employ a
multi-level nested-loop structure. With a single-level loop, use of the decrement and test, DTRn,
and conditional delayed branch BF/S instructions supported by the SH-3 is adequate. However,
with nested loops, DSP performance can be improved by means of a zero-overhead loop control
function.
The RS, RE, and MOD registers have been added to support loop control and modulo addressing
functions. Instructions are supported for data transfer between these new control registers and
general registers or memory. In addition, the LDRS and LDRE address calculation registers have
been added to reduce the code size for the initial settings for zero-overhead loop control.
An independent control register, DSR, is provided for the DSP engine. This register is treated as a
system register such as MACL and MACH. The A0, X0, X1, Y0, and Y1 registers are treated as
system registers from the CPU side, and LDS/STS instructions are supported for the same
purpose. Table 2.25 shows the instruction code map for the new system control instructions for the
CPU core.
Group 2 instructions are provided to reduce DSP operation program code size. Data transfer
instructions that perform no data processing are frequently executed by the DSP engine. In this
case, a 32-bit instruction code is unnecessarily long, and wastes space in the program memory
area. All instructions in this class have a 16-bit code length, the same as conventional SH core
instructions. Single data transfer instructions have greater flexibility in terms of operands than the
double data transfer instruction or parallel instruction class.
Group 3 instructions are provided for fast execution of digital signal processing operations using
the DSP unit. These instructions have a 32-bit instruction code, so that a maximum of four
instructions—an ALU operation, multiplication, and two data transfer instructions—can be
executed in parallel.