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IDT
Understanding the Instruction Set
79RC32355 User Reference Manual
A - 2
November 4, 2002
Notes
Figure A.1 Example of Instruction Description
Instruction Fields
Fields encoding the instruction word are shown in register form at the top of the instruction description.
The following rules are followed:
The values of constant fields and the opcode names for opcode fields are listed in uppercase (SPE-
CIAL and ADD in Figure A.1).
All variable fields are listed with the lowercase names used in the instruction description (rs, rt and
rd in Figure A.1).
Fields that contain zeros but are not named are unused fields that are required to be zero (bits 10:6
Instruction mnemonic and
descriptive name
Instruction encoding
constant and variable field
names and values
Architecture level at which
instruction was defined/
redefined and assembler
format(s) for each definition
Short description
Symbolic description
Full description of instruction
operation
Restrictions on instruction
and operands
High-level language
description of instruction
operation
Exceptions that instruction
can cause
Notes for programmers
Notes for implementors
Example Instruction Name
Example
31
25
26
20
21
15
16
SPECIAL
0 0 0 0 0 0
rs
rt
6
5
5
rd
0
EXAMPLE
0 0 0 0 0 0
5
5
6
11
10
6
5
0
0 0 0 0 0
Format:
EXAMPLE rd, rs,rt
MIPS32
Purpose:
to execute an EXAMPE op
Description:
rd rs exampleop rt.
This section describes the operation of the instruction in text, tables, and illustra-
tions. It includes information that would be difficult to encode in the Operation
section.
Restrictions:
This section lists any restrictions for the instruction. This can include values of
the instruction encoding fields such as register specifiers, operand values, oper-
and formats, address alignment, instruction scheduling hazards, and type of
memory access for addressed locations.
Operation:
/* This section describes the operation of an instruction in a */
/* high-level pseudo-language. It is precise in ways that the */
/* Description section is not, but is also missing information */
/* that is hard to express in pseudocode.*/
temp GPR[rs] exampleop GPR[rt]
GPR[rd] temp
Exceptions:
A list of exceptions taken by the instruction
Programming Notes:
Information useful to programmers, but not necessary to describe the operation
of the instruction
Implementation Notes:
Like
Programming Notes
, except for processor implementors