Atmel CAVR-4 Manual De Usuario

CAVR-4

Part 1. Using the compiler

This chapter gives a brief introduction to the memory layout of the AVR 

microcontroller and the fundamental ways data can be stored in memory: on 

the stack, in static (global) memory, or in heap memory. For efficient memory 

usage, AVR IAR C/C++ Compiler provides a set of memory models and 

memory attributes, allowing you to fine-tune the access methods, resulting in 

smaller code size. The concepts of memory models and memory types are 

described in relation to pointers, structures, C++ class objects, and 

non-initialized memory. Finally, detailed information about data storage on the 

stack and the heap is provided.

The AVR microcontroller is based on the Harvard architecture—thus code and data have 
separate memory spaces and require different access mechanisms. Code and different 
type of data are located in memory spaces as follows:

●

The internal flash space, which is used for code, 

_ _flash

 declared objects, and 

initializers

●

The data space, which can consist of external ROM, used for constants, and RAM 
areas used for the stack, for registers, and for variables

●

The EEPROM space, which is used for variables.

In a typical application, data can be stored in memory in three different ways:

●

On the stack. This is memory space that can be used by a function as long as it is 
executing. When the function returns to its caller, the memory space is no longer 
valid.

●

Static memory. This kind of memory is allocated once and for all; it remains valid 
through the entire execution of the application. Variables that are either global or 
declared static are placed in this type of memory. The word static in this context 
means that the amount of memory allocated for this type of variable does not 
change while the application is running.