LoadRx, StoreRx, and TestRx Macros

Coding Guidelines, Rev. 1

Freescale Semiconductor

2-1

Preliminary

Chapter 2 Coding Guidelines

This section explains how the user’s source code should be developed in order to

generate code for both the SDM and LDM.

2.1 Type Casting Pointers

When developing software for the SDM, do not type cast pointers to be 16 bits (i.e.,

unsigned int). This will work for the SDM, but if you switch to the LDM, it may not work,

because your pointer size may be greater than 16 bits.

2.2 Conversion of 56800 Instructions to 56800E Instructions

When the 56800E was developed, one requirement was the ability to use all of the

56800 instructions to easily upgrade from the 56800 to the 56800E. This approach

works fine for the SDM; however, since the 56800 instructions are for a 16-bit controller

with 16-bit pointers, this approach is no longer valid when using the LDM.

When using the LDM, the “allow legacy instructions” Language Settings: M56800E

Assembler option must be turned off and the user must convert all 56800 instructions to

56800E instructions. Please see the DSP56800 to DSP56800E Porting Guide to learn

more.

2.3 LoadRx, StoreRx, and TestRx Macros

When loading, storing, or testing pointers in Assembly, you must specify if it is a word or

a long. For the SDM, pointers are a word and for the LDM, pointers are a long.

Depending on the model, defined macros in portasm.h ease switching from SDM to

LDM and vice versa. These assembly macros (LoadRx, StoreRx, and TestRx) are

defined based on which model is used, so they load, store, and test the correct size of

the pointer.