Alarm Clock

Reimplement timer_sleep(), defined in devices/timer.c.

Although a working implementation is provided, it busy waits, that is, it spins in a loop checking the current time and calling thread_yield() until enough time has gone by. Reimplement it to avoid busy waiting.

void timer_sleep (int64_t ticks);

Suspends execution of the calling thread until time has advanced by at least x timer ticks. Unless the system is otherwise idle, the thread need not wake up after exactly x ticks. Just put it on the ready queue after they have waited for the right amount of time.

timer_sleep() is useful for threads that operate in real-time, e.g. for blinking the cursor once per second. The argument to timer_sleep() is expressed in timer ticks, not in milliseconds or any another unit. There are TIMER_FREQ timer ticks per second, where TIMER_FREQ is a macro defined in devices/timer.h. The default value is 100. We don't recommend changing this value, because any change is likely to cause many of the tests to fail.

Separate functions timer_msleep(), timer_usleep(), and timer_nsleep() do exist for sleeping a specific number of milliseconds, microseconds, or nanoseconds, respectively, but these will call timer_sleep() automatically when necessary. You do not need to modify them. The alarm clock implementation is not needed for later projects, although it could be useful for project 4.

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