User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
that the architecture specification refers to simplified mnemonics as extended mnemonics. Programs written to be portable across the various assemblers for the PowerPC Architecture should not assume the existence of mnemonics not described in that document.
2.3.1 Classes of InstructionsThe 750GX instructions belong to one of the following three classes.
•Defined
•Illegal
•Reserved
Note that while the definitions of these terms are consistent among the PowerPC processors, the assignment of these classifications is not. For example, PowerPC instructions defined for
The class is determined by examining the primary opcode and the extended opcode, if any. If the opcode, or combination of opcode and extended opcode, is not that of a defined instruction or of a reserved instruction, the instruction is illegal.
Instruction encodings that are now illegal might be assigned to instructions in the architecture or might be reserved by being assigned to
If instructions are encoded with incorrectly set bits in reserved fields, the results on execution can be said to be boundedly undefined. If a
Defined instructions are guaranteed to be supported in all PowerPC implementations, except as stated in the instruction descriptions in Chapter 8, “Instruction Set,” of the the PowerPC Microprocessor Family: The Programming Environments Manual. The 750GX provides hardware support for all instructions defined for
It does not support the optional Floating Square Root
A PowerPC processor 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. Note that the architecture specification refers to exceptions as interrupts.
A defined instruction can have invalid forms. The 750GX provides limited support for instructions represented in an invalid form.
gx_02.fm.(1.2) | Programming Model |
March 27, 2006 | Page 87 of 377 |