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Chapter 2. Programming Model
2-1
Chapter 2
Programming Model
This chapter describes the MPC7400 programming model, emphasizing those features
speciTc to the MPC7400 processor and summarizing those that are common to PowerPC
processors. It consists of three major sections, which describe the following:
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Registers implemented in the MPC7400
Operand conventions
The MPC7400 instruction set
For detailed information about architecture-deTned features, see
The
Programming
Environments Manual
and
The AltiVec Technology Programming Environments Manual
.
AltiVec Technology and the Programming Model
AltiVec features are described in the following sections:
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Three additional registersVRs, VRSAVE, and VSCR. See Section 7.1, òAltiVec
Technology and the Programming Model.ó
2.1 The MPC7400 Processor Register Set
This section describes the registers implemented in the MPC7400. It includes an overview
of registers deTned by the PowerPC architecture and the AltiVec technology, highlighting
differences in how these registers are implemented in the MPC7400, and a detailed
description of MPC7400-speciTc registers. Full descriptions of the architecture-deTned
register set are provided in Chapter 2, òPowerPC Register Set,ó in
The Programming
Environments Manual
and Chapter 2, òAltiVec Register Set,ó in
The AltiVec Technology
Programming Environments Manual
.
Registers are deTned at all three levels of the PowerPC architectureuser instruction set
architecture (UISA), virtual environment architecture (VEA), and operating environment
architecture (OEA). The PowerPC architecture deTnes register-to-register operations for all
computational instructions. Source data for these instructions are accessed from the on-chip
registers or are provided as immediate values embedded in the opcode. The three-register
instruction format allows speciTcation of a target register distinct from the two source
registers, thus preserving the original data for use by other instructions and reducing the
number of instructions required for certain operations. Data is transferred between memory
and registers with explicit load and store instructions only.