
MOTOROLA
Chapter 3. Instruction Set Model
3-7
Instruction Set Summary
3.2.1.2
Defined Instruction Class
Defined instructions are guaranteed to be supported in all PowerPC implementations,
except as stated in the instruction descriptions in Chapter 8, “Instruction Set,” in the
Programming Environments Manual
. The G2 core provides hardware support for all
instructions defined for 32-bit implementations.
A processor of this family invokes the illegal instruction error handler (part of the program
exception) when the unimplemented PowerPC instructions are encountered so they can be
emulated in software, as required.
A defined instruction can have invalid forms, as described in the following section.
3.2.1.3
Illegal Instruction Class
Illegal instructions are grouped into the following categories:
Instructions not defined in the PowerPC architecture. These opcodes are available
for future extensions of the PowerPC architecture; that is, future versions of the
PowerPC architecture may define any of these instructions to perform new
functions.
The following primary opcodes are defined as illegal but may be used in future
extensions to the architecture:
1, 4, 5, 6, 9, 22, 56, 57, 60, 61
Instructions defined in the PowerPC architecture but not implemented in a specific
PowerPC implementation. For example, instructions that can be executed on 64-bit
processors are considered illegal by 32-bit processor cores.
The following primary opcodes are defined for 64-bit implementations only and are
illegal on the core:
2, 30, 58, 62
All unused extended opcodes are illegal. The unused extended opcodes can be
determined from information in Appendix A.2, “Instructions Sorted by Opcode,”
and Section 3.2.1.4, “Reserved Instruction Class.” Notice that extended opcodes for
instructions that are defined only for 64-bit implementations are illegal in 32-bit
implementations, and vice versa.
The following primary opcodes have unused extended opcodes:
17, 19, 31, 59, 63 (primary opcodes 30 and 62 are illegal for all 32-bit
implementations, but as 64-bit opcodes they have some unused extended
opcodes)
An instruction consisting entirely of zeros is guaranteed to be an illegal instruction.
This increases the probability that an attempt to execute data or uninitialized
memory invokes the system illegal instruction error handler (a program exception).
Note that if only the primary opcode consists of all zeros, the instruction is
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