
RCPU
REFERENCE MANUAL
OVERVIEW
MOTOROLA
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1.2 Levels of the PowerPC Architecture
The PowerPC architecture consists of three layers. Adherence to the PowerPC ar-
chitecture can be measured in terms of which of the following levels of the archi-
tecture are implemented:
PowerPC user instruction set architecture (UISA) — Defines the base user-
level instruction set, user-level registers, data types, floating-point exception
model, memory models for a uniprocessor environment, and programming
model for a uniprocessor environment.
PowerPC virtual environment architecture (VEA) — Describes the memory
model for a multiprocessor environment, defines cache control instructions,
and describes other aspects of virtual environments. Implementations that
conform to the VEA also adhere to the UISA, but may not necessarily adhere
to the OEA.
PowerPC operating environment architecture (OEA) — Defines the memory
management model, supervisor-level registers, synchronization require-
ments, and the exception model. Implementations that conform to the OEA
also adhere to the UISA and the VEA.
1.3 The RCPU as a PowerPC Implementation
This subsection describes the RCPU as a member of the PowerPC processor
family.
1.3.1 PowerPC Registers and Programming Model
The PowerPC architecture defines register-to-register operations for most compu-
tational 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
memory and on-chip registers.
PowerPC processors have 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 Pow-
erPC processor also has its own unique set of implementation-specific registers.
The RCPU is a 32-bit implementation of the PowerPC architecture. In the RCPU,
the time base and FPRs are 64 bits; all other registers are 32 bits.
The following sections summarize the PowerPC registers that are implemented in
the RCPU. Refer to
SECTION 2 REGISTERS
for detailed descriptions of PowerPC
registers. In addition, for descriptions of the I-cache control registers, refer to
SEC-
TION 5 INSTRUCTION CACHE
. For details on development-support registers, re-
fer to
SECTION 8 DEVELOPMENT SUPPORT
.
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