In general, it is beneficial to separate all system initialization code from the main application. However, some components of system initialization, for example, enabling of caches and interrupts, must occur after executing C library initialization code.

You can make use of the $Sub and $Super function wrapper symbols to (effectively) insert a routine that is executed immediately before entering the main application. This mechanism enables you to extend functions without altering the source code.

Example 2.12 shows how $Sub and $Super can be used in this way. The linker replaces the function call to main() with a call to $Sub$$main(). From there you can call a routine that enables caches and another to enable interrupts.

The code branches to the real main() by calling $Super$$main().

extern void $Super$$main(void);

void $Sub$$main(void)
{
    cache_enable();    // enables caches
    int_enable(); 		     // enables interrupts 
    $Super$$main();    // calls original main()
}