Specifications

CAVR-4

Introduction to the runtime environment

AVR® IAR C/C++ Compiler

Reference Guide

The runtime library is delivered both as prebuilt libraries and as source files, and you

can find them in the product subdirectories avr\lib and avr\src, respectively.

The runtime environment also consists of a part with specific support for the target

system, which includes:

● Support for hardware features:

● Direct access to low-level processor operations by means of intrinsic functions,

such as functions for register handling

● Peripheral unit registers and interrupt definitions in include files

● Special compiler support for accessing strings in flash memory, see AVR–specific

library functions, page 249

● Runtime environment support, that is, startup and exit code and low-level interface

to some library functions.

Some parts, like the startup and exit code and the size of the heaps must be tailored for

the specific hardware and application requirements.

For further information about the library, see the chapter Library functions.

LIBRARY SELECTION

To configure the most code-efficient runtime environment, you must determine your

application and hardware requirements. The more functionality you need, the larger

your code will get.

IAR Embedded Workbench comes with a set of prebuilt runtime libraries. To get the

required runtime environment, you can customize it by:

● Setting library options, for example, for choosing scanf input and printf output

formatters, and for specifying the size of the stack and the heap

● Overriding certain library functions, for example cstartup.s90, with your own

customized versions

● Choosing the level of support for certain standard library functionality, for example,

locale, file descriptors, and multibytes, by choosing a library configuration: normal

or full.

In addition, you can also make your own library configuration, but that requires that you

rebuild the library. This allows you to get full control of the runtime environment.

Note: Your application project must be able to locate the library, include files, and the

library configuration file.