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IAR Embedded Workbench for RL78 5.20

System startup and termination

In this section:

This section describes the runtime environment actions performed during startup and termination of your application.

The code for handling startup and termination is located in the source files cstartup.s, cexit.s, and low_level_init.c located in the rl78\src\lib directory.

For information about how to customize the system startup code, see System initialization.

System startup

During system startup, an initialization sequence is executed before the main function is entered. This sequence performs initializations required for the target hardware and the C/C++ environment.

For the hardware initialization, it looks like this:

SystemStartup1 70percent.png

  • When the CPU is reset it will start executing at the program entry label__iar_program_start in the system startup code.

  • The stack pointer is initialized

  • The function __low_level_init is called if you defined it, giving the application a chance to perform early initializations.

For the C/C++ initialization, it looks like this:

SystemStartup2 70percent.png

  • Static and global variables are initialized. That is, zero-initialized variables are cleared and the values of other initialized variables are copied from ROM to RAM memory. This step is skipped if __low_level_init returns zero. For more information, see Initialization at system startup.

  • Static C++ objects are constructed

  • The main function is called, which starts the application.

For information about the initialization phase, see Application execution—an overview.

System termination

This illustration shows the different ways an embedded application can terminate in a controlled way:

SystemTermination 70percent.png

An application can terminate normally in two different ways:

  • Return from the main function

  • Call the exit function.

Because the 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 assembler function _exit that will:

  • 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 function atexit. See also Setting up the atexit limit.

  • Close all open files

  • Call __exit

  • When __exit is reached, stop the system.

An application can also exit by calling the abort, the _Exit, or the quick_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. The quick_exit function is equivalent to the _Exit function, except that it calls each function passed to at_quick_exit before calling __exit.

If you want your application to do anything extra at exit, for example, resetting the system (and if using atexit is not sufficient), you can write your own implementation of the __exit(int) function.

The library files that you can override with your own versions are located in the rl78\src\lib directory. See Overriding library modules.

C-SPY debugging support for system termination

If you have enabled C-SPY emulated I/O during linking, the normal __exitand abort functions are replaced with special ones. C-SPY will then recognize when those functions are called and can take appropriate actions to emulate program termination. For more information, see Briefly about C-SPY emulated I/O.