the interrupt handler. If the event callback starts a new short timeout,
the timer can fire before returning from the event callback, and clearing
the interrupt status after that loses the interrupt and hangs until the
counter wraps. Fixing all of this removes the need for the do-nothing
loop at the top of the handler which really just waited for the counter to
roll over and reach the one-shot count again.
Also add a missing return(0) in the periodic timer start case.
54fe60971c