Watchdog timer with interrupt support

[simonklee]

Was playing around with watchdog resets and added support for the watchdog interrupt timers. <avr/wdt.h> has watchdog timer reset support, but lacks the possibility to set the watchdog timer for interrupts. An example application follows.

wdt_interrupt {                    
    wdt_reset();         
    wdt_interrupt_enable();                                                                  
}                                                                         
__attribute__((noreturn)) int main (void) {                      
    wdt_reset();                                                                    
    wdt_interrupt_enable();                    
    wdt_change_clock(1024);

    sleep_mode_power_down();                                                                            
    sei();                                                                                        

    while(1) {
        /* bring avr to sleep code */
    }
}

The watchdog interrupt wakes the avr from power-down sleep mode every ~8 sec. I'm not really sure if the code I've written here is any good, especially in regards to the enabling/disabling the WD and changing prescaler settings. These routines need some extra care (see datasheets) and I solved that in the most straightforward way I could think of. So if you have some suggestions to how to do this in a better way I'm happy to modify the code.