Chapter 2. Programming Model
2-39
Instruction Set Summary
See òProgram Exception (0x0_0700),ó in Chapter 6, òExceptions,ó in
The Programming
Environments Manual
for information about illegal and invalid instruction exceptions.
The PowerPC architecture deTnes four types of reserved instructions:
¥
Instructions in the POWER architecture not part of the PowerPC UISA. For details
on POWER architecture incompatibilities and how they are handled by PowerPC
processors, see Appendix B, òPOWER Architecture Cross Reference,ó in
The
Programming Environments Manual
.
Implementation-speciTc instructions required for the processor to conform to the
PowerPC architecture (none of these are implemented in the MPC7400)
All other implementation-speciTc instructions
Architecturally-allowed extended opcodes
¥
¥
¥
2.3.2 Addressing Modes
This section provides an overview of conventions for addressing memory and for
calculating effective addresses as deTned by the PowerPC architecture for 32-bit
implementations. For more detailed information, see òConventions,ó in Chapter 4,
òAddressing Modes and Instruction Set Summary,ó of
The Programming Environments
Manual
.
2.3.2.1 Memory Addressing
A program references memory using the effective (logical) address computed by the
processor when it executes a memory access or branch instruction or when it fetches the
next sequential instruction.
Bytes in memory are numbered consecutively starting with zero. Each number is the
address of the corresponding byte.
2.3.2.2 Memory Operands
Memory operands can be bytes, half words, words, double words, or quad words or, for the
load/store multiple and load/store string instructions, a sequence of bytes or words. The
address of a memory operand is the address of its Trst byte (that is, of its lowest-numbered
byte). Operand length is implicit for each instruction. The PowerPC architecture supports
both big-endian and little-endian byte ordering. The default byte and bit ordering is
big-endian. See òByte Ordering,ó in Chapter 3, òOperand Conventions,ó of
The
Programming Environments Manual
for more information about big- and little-endian byte
ordering.
The operand of a single-register memory access instruction has a natural alignment
boundary equal to the operand length. In other words, the ònaturaló address of an operand
is an integral multiple of the operand length. A memory operand is said to be aligned if it
is aligned at its natural boundary; otherwise it is misaligned. For a detailed discussion about