Atmel CAVR-4 Manual De Usuario

CAVR-4

Part1. Using the compiler

For embedded systems, the size of the generated code and data is very 

important, because using smaller external memory or on-chip memory can 

significantly decrease the cost and power consumption of a system.

This chapter gives an overview about how to write code that compiles to 

efficient code for an embedded application. The issues discussed are:

●

Taking advantage of the compilation system

●

Selecting data types and placing data in memory

●

Writing efficient code.

As a part of this, the chapter also demonstrates some of the more common 

mistakes and how to avoid them, and gives a catalog of good coding 

techniques.

Largely, the compiler determines what size the executable code for the application will 
be. The compiler performs many transformations on a program in order to generate the 
best possible code. Examples of such transformations are storing values in registers 
instead of memory, removing superfluous code, reordering computations in a more 
efficient order, and replacing arithmetic operations by cheaper operations.

The linker should also be considered an integral part of the compilation system, since 
there are some optimizations that are performed by the linker. For instance, all unused 
functions and variables are removed and not included in the final object file. It is also as 
input to the linker you specify the memory layout. For detailed information about how 
to design the linker command file to suit the memory layout of your target system, see 
the chapter Placing code and data.