Atmel CAVR-4 Manual De Usuario

CAVR-4

Part 1. Using the compiler

When an application is initialized, a number of steps are performed:

●

When the cpu is reset it will jump to the program entry label 

_ _program_start

 in 

the system startup code.

●

Enables the external data and address buses if needed

●

Initializes the stack pointers to the end of 

CSTACK

 and 

RSTACK

, respectively

●

The function 

_ _low_level_init

 is called, giving the application a chance to 

perform early initializations

●

Static variables are initialized except for 

_ _no_init

 and 

_ _eeprom

 declared 

variables; this includes clearing zero-initialized memory and copying the ROM 
image of the RAM memory of the rest of the initialized variables depending on the 
return value of 

_ _low_level_init

●

Static C++ objects are constructed

●

The 

main

 function is called, which starts the application.

An application can terminate normally in two different ways:

●

Return from the 

main

 function

●

Call the 

exit

 function.

As the ISO/ANSI C standard states that the two methods should be equivalent, the 
system startup code calls the 

exit

 function if 

main

 returns. The parameter passed to the 

exit

 function is the return value of 

main

.

The default 

exit

 function is written in C. It calls a small function 

_exit

, also written 

in C, that will perform the following operations:

●

Call functions registered to be executed when the application ends. This includes 
C++ destructors for static and global variables, and functions registered with the 
standard C function 

atexit

●

Close all open files

●

Call 

_ _exit

●

When 

_ _exit

 is reached, stop the system.

An application can also exit by calling the 

abort

 or the 

_Exit

 function. The 

abort

 

function just calls 

_ _exit

 to halt the system, and does not perform any type of cleanup. 

The 

_Exit

 function is equivalent to the 

abort

 function, except for the fact that 

_Exit

 

takes an argument for passing exit status information.

If you want your application to perform anything extra at exit, for example resetting the 
system, you can write your own implementation of the 

_ _exit(int)

 function.