Motorola MPC860 PowerQUICC User Manual page 154

Part II. PowerPC Microprocessor Module
6.2.1.1 DeÞnition of Boundedly UndeÞned
If instructions are encoded with incorrectly set bits in reserved Þelds, the results on
execution can be said to be boundedly undeÞned. If a user-level program executes the
incorrectly coded instruction, the resulting undeÞned results are bounded in that a spurious
change from user to supervisor state is not allowed, and the level of privilege exercised by
the program in relation to memory access and other system resources cannot be exceeded.
Boundedly undeÞned results for a given instruction may vary between implementations,
and between execution attempts in the same implementation.
6.2.1.2 DeÞned Instruction Class
DeÞned instructions are guaranteed to be supported in all PowerPC implementations,
except as stated in the instruction descriptions in Chapter 8, ÒInstruction Set,Ó in The
Programming Environments Manual. The MPC860 provides hardware support for all
instructions deÞned for 32-bit implementations, except ßoating-point instructions.
A PowerPC processor invokes the illegal instruction error handler (part of the program
exception) when the unimplemented PowerPC instructions are encountered so they may be
emulated in software, as required.
A deÞned instruction can have invalid forms, as described in the following section.
6.2.1.3 Illegal Instruction Class
Illegal instructions can be grouped into the following categories:
¥ Instructions that are not implemented 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 deÞned as illegal but may be used in future
extensions to the architecture:
1, 4, 5, 6, 9, 22, 56, 57, 60, 61
¥ Instructions that are implemented in the PowerPC architecture but are not
implemented in a specific PowerPC implementation. For example, instructions that
can be executed on 64-bit PowerPC processors are considered illegal by 32-bit
processors.
The following primary opcodes are defined for 64-bit implementations only and are
illegal on the MPC860:
2, 30, 58, 62
¥ All unused extended opcodes are illegal. The unused extended opcodes can be
determined from information in Section A.2, ÒInstructions Sorted by Opcode,Ó in
the Programming Environments Manual and Section 6.2.1.4, ÒReserved Instruction
Class.Ó Notice that extended opcodes for instructions that are defined only for 64-bit
implementations are illegal in 32-bit implementations, and vice versa.
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