Wraparound of timer

[claudioscordino]

There is a wraparound on CLINT_MTIMECMP (function timer_handler() inside 04-TimerInterrupt/timer.c).
If you set the interval to 1000000, the wraparound occurs just after a few minutes of Qemu running.
Once the wraparound has occurred, the timer starts firing at an extremely tiny delay (of course different than the one that was set).