Technical information

 Introduction 1

1 Introduction

The DSP56800E’s DSP core architecture represents the next step in the evolution of Motorola’s 16-bit

DSP56800 Family of digital signal processors. It maintains compatibility with the DSP56800 while

improving performance and adding new features.

Some of the new and useful features of the DSP56800E (as compared to the DSP56800) that can be

exploited for optimization include:

• Additional registers (accumulators, pointers, and an offset register)

• Extended set of data ALU operations

• AGU arithmetic

• Support for nested DO looping

• New data types (byte and long)

• 24-bit data memory address space and 21-bit program memory address space

• Support for real-time debugging (Enhanced OnCE™)

An important feature of the DSP56800E is its source code compatibility with the DSP56800. Code

developed for the DSP56800 can be assembled for the DSP56800E and will run correctly if certain coding

requirements are fulfilled. These requirements are not very restrictive. They are identified, analyzed,

fulfilled, and verified with regard to example code in this application note. If these requirements are not

met in the initial application, the necessary changes are easy to implement.

The sample code that was ported to the DSP56800E executed in half the number of cycles required by the

DSP56800, even without any optimization (without exploiting the new features of the DSP56800E).

Whereas the DSP56800 typically completes execution of an instruction in 2 cycles, the DSP56800E

performs the same job in 1 cycle. Moreover, code written for the DSP56800 can be further optimized

because of the new features introduced in the DSP56800E.

Another difference between the DSP56800E and the DSP56800 is new pipeline behavior. Although this

behavior does not affect code correctness, in some cases it can introduce stalls. The programmer can avoid

these situations by rearranging instructions.

The main purpose of this application note is to recommend a method for porting DSP56800 applications to

the DSP56800E and for optimizing the applications, exploiting the advantages of the new architecture.

This document also details some aspects of the following issues:

• The relative benefit of rewriting a function from scratch compared to porting and optimizing the

application

• How pipeline effects on the DSP56800E can affect the ported code

• How an application can be translated beyond the 64 kwords boundary for program and data memory

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Freescale Semiconductor, Inc.

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