4.9.1 The main Function

The identifier main is special. You must always have one, and only one, function called main() in your programs. This is the first C function to execute in your program.

Since your program is not called by a host, the compiler inserts special code at the end of main(), which is executed if this function ends, i.e., a return statement inside main() is executed, or code execution reaches the main()’s terminating right brace. This special code causes execution to jump to address 0, the Reset vector for all 8-bit AVR devices. This essentially performs a software Reset. Note that the state of registers after a software Reset can be different from that after a hardware Reset.

It is recommended that the main() function does not end. Place all or some of your code in main() within a loop construct (such as a while(1)) that will never terminate. For example,

int main(void)
{
    // your code goes here
    // finished that, now just wait for interrupts
    while(1)
        continue;
}