User`s guide

C for DSP56800E

Deadstripping and Link Order

133Targeting MC56F83xx/DSP5685x Controllers

for (i=0; i<100; i++) { MyFunc(i); }

for (j=0; j<100; j++) { MyFunc(j); }

However, if the code included the expression MyFunc (i+j), the variables would

be in use at the same time. The compiler would store the two variables in different

registers.

For DSP56800E development, you can instruct the compiler to:

1. Store all local variables on the stack. — (That is, do not perform register

coloring.) The compiler loads and stores local variables when you read them and

write to them. You may prefer this behavior during debugging, because it

guarantees meaningful values for all variables, from initialization through the end

of the function. To have the compiler behave this way, specify optimization

Level 0, in the Global Optimizations settings panel.

2. Place as many local variables as possible in registers. — (That is, do perform

Level 1 or higher, in the Global Optimizations settings panel.

NOTE

Optimization Level 0 is best for code that you will debug after

compilation. Other optimization levels include register coloring. If

you compile code with an optimization level greater than 0, then

debug the code, register coloring could produce unexpected results.

Variables declared volatile (or those that have the address taken) are not kept

in registers and may be useful in the presence of interrupts.

3. Run Peephole Optimization. — The compiler eliminates some compare

instructions and improves branch sequences. Peephole optimizations are small

and local optimizations that eliminate some compare instructions and improve

branch sequences. To have the compiler behave this way, specify optimization

Levels 1 through 4, in the Global Optimizations settings panel.

Deadstripping and Link Order

The M56800E Linker deadstrips unused code and data only from files compiled by the

CodeWarrior C compiler. The linker never deadstrips assembler relocatable files or C

object files built by other compilers.