
MOTOROLA
Chapter 1. Overview
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Implementation-Specific Information
The following sections summarize the features of the core, including both those that are
defined by the architecture and those that are unique to the various core implementations.
Specific features of the core are listed in Section 1.1.1, “Features.”
1.3.1
Register Model
The PowerPC architecture defines register-to-register operations for most computational
instructions. Source operands for these instructions are accessed from the registers or are
provided as immediate values embedded in the instruction opcode. The three-register
instruction format allows specification of a target register distinct from the two-source
operands. Load and store instructions transfer data between registers and memory.
The G2 core has two levels of privilege—supervisor mode of operation (typically used by
the operating system) and user mode of operation (used by the application software). The
programming models incorporate 32 GPRs, 32 FPRs, special-purpose registers (SPRs), and
several miscellaneous registers. Each core also has its own unique set of hardware
implementation (HID) registers.
Having access to privileged instructions, registers, and other resources allows the operating
system to control the application environment (providing virtual memory and protecting
operating system and critical machine resources). Instructions that control the state of the
G2 core, the address translation mechanism, and supervisor registers can be executed only
when the core is operating in supervisor mode.
Figure 1-2 shows all the core registers available at the user and supervisor level. The
numbers to the right of the SPRs indicate the number that is used in the syntax of the
instruction operands for the move to/from SPR instructions.
The following sections describe the G2 core implementation-specific features as they apply
to registers.
1.3.1.1
General-Purpose Registers (GPRs)
The PowerPC architecture defines 32 user-level GPRs, which are 32 bits wide in 32-bit
cores. The GPRs serve as the data source or destination for all integer instructions.
1.3.1.2
Floating-Point Registers (FPRs)
The PowerPC architecture also defines 32 user-level, 64-bit FPRs. The FPRs serve as the
data source or destination for floating-point instructions. These registers can contain data
objects of either single- or double-precision floating-point formats.
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