VR4102 datasheet(46/701 Pages) NEC

46 / 701 page

CHAPTER 1 INTRODUCTION

1.5.3 CPU Instruction Set Overview

Each CPU instruction is 32 bits long. As shown in Figure 1-4, there are three instruction formats:

— immediate (I-type)

— jump (J-type)

— register (R-type)

Figure 1-4. CPU Instruction Formats

I-type (immediate)

J-type (jump)

target

R-type (register)

immediate

funct

The instruction set can be further divided into the following five groupings:

(1) Load and store instructions move data between memory and general-purpose registers.

They are all

immediate (I-type) instructions, since the only addressing mode supported is base register plus 16-bit,

signed immediate offset.

(2) Computational instructions perform arithmetic, logical, shift, multiply, and divide operations on values in

registers. They include R-type (in which both the operands and the result are stored in registers) and I-type

(in which one operand is a 16-bit signed immediate value) formats.

(3) Jump and branch instructions change the control flow of a program. Jumps are always made to an absolute

address formed by combining a 26-bit target address with the high-order bits of the Program Counter (J-type

format) or register address (R-type format). The format of the branch instructions is I type. Branches have

16-bit offsets relative to the Program Counter. JAL instructions save their return address in register 31.

(4) Coprocessor 0 (System Control Coprocessor, CP0) instructions perform operations on CP0 registers to

control the memory-management and exception-handling facilities of the processor.

(5) Special instructions perform system calls and breakpoint operations, or cause a branch to the general

exception-handling vector based upon the result of a comparison. These instructions occur in both R-type

(both the operands and the result are stored in registers) and I-type (one operand is a 16-bit signed

immediate value) formats.

Chapter 3 provides a more detailed summary (Refer to Chapter 27 for detailed descriptions of the operation of

each instruction) .

VR4102 Datasheet(PDF) 46 Page - NEC