Specifications

CAVR-4

Part 1. Using the compiler

Functions

Special function types

This section describes the special function types interrupt and monitor. The AVR IAR

C/C++ Compiler allows an application to take full advantage of these AVR features,

without forcing you to implement anything in assembler language.

INTERRUPT FUNCTIONS

In embedded systems, the use of interrupts is a method of detecting external events

immediately; for example, detecting that a button has been pressed.

In general, when an interrupt occurs in the code, the microcontroller simply stops

executing the code it runs, and starts executing an interrupt routine instead. It is

imperative that the environment of the interrupted function is restored; this includes the

values of processor registers and the processor status register. This makes it possible to

continue the execution of the original code when the code that handled the interrupt has

been executed.

The AVR microcontroller supports many interrupt sources. For each interrupt source, an

interrupt routine can be written. Each interrupt routine is associated with a vector

number, alternatively multiple vector numbers, which is specified in the AVR

microcontroller documentation from the chip manufacturer. The header file

ioderivative.h, where derivative corresponds to the selected derivative, contains

predefined names for the existing exception vectors.

To define an interrupt function, the

__interrupt keyword and the #pragma vector

directive can be used. For example:

#pragma vector=0x14

__interrupt void my_interrupt_routine(void)

{

/* Do something */

}

Note: An interrupt function must have the return type void, and it cannot specify any

parameters.

If a vector is specified in the definition of an interrupt function, the processor interrupt

vector table is populated. It is also possible to define an interrupt function without a

vector. This is useful if an application is capable of populating or changing the interrupt

vector table at runtime. See the chip manufacturer’s AVR microcontroller

documentation for more information about the interrupt vector table.