
3-8
G2 PowerPC Core Reference Manual
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MOTOROLA
Instruction Set Summary
considered a reserved instruction. This is further described in Section 3.2.1.4,
“Reserved Instruction Class.”
An attempt to execute an illegal instruction invokes the illegal instruction error handler (a
program exception) but has no other effect. Section 5.5.7, “Program Exception (0x00700),”
describes illegal and invalid instruction exceptions.
Except for an instruction consisting entirely of binary zeros, illegal instructions are
available for further additions to the PowerPC architecture.
3.2.1.4
Reserved Instruction Class
Reserved instructions are allocated to specific implementation-dependent purposes not
defined by the PowerPC architecture. An attempt to execute an unimplemented reserved
instruction invokes the illegal instruction error handler (a program exception). See
Section 5.5.7, “Program Exception (0x00700),” for additional information about illegal
and invalid instruction exceptions.
The following types of instructions are included in this class:
Implementation-specific instructions (for example, Load Data TLB Entry (
tlbld
)
and Load Instruction TLB Entry (
tlbli
) instructions).
Optional instructions defined by the PowerPC architecture but not implemented by
the core (for example, Floating Square Root (
fsqrt
) and Floating Square Root Single
(
fsqrts
) instructions).
3.2.2
Addressing Modes
This section provides an overview of conventions for addressing memory and calculating
effective addresses as defined by the PowerPC architecture for 32-bit implementations. For
more detailed information, see “Conventions” in Chapter 4, “Addressing Modes and
Instruction Set Summary,” of the
Programming Environments Manual
.
3.2.2.1
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.
As described in Section 3.1.1, “Data Organization in Memory and Memory Operands,”
bytes in memory are numbered consecutively starting with zero. Each number is the
address of the corresponding byte.
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