DEFINITION MODULE Timer;

	(********************************************************)
	(*							*)
	(*	Clock handler for operating system.		*)
	(*							*)
	(*	Author:		P. Moylan			*)
	(*	Last edited:	27 May 1989			*)
	(*	Description:					*)
	(*		This module contains the clock		*)
	(*		interrupt routine.  It checks whether	*)
	(*		the current task has used its time	*)
	(*		quota, also keeps track of sleeping	*)
	(*		tasks.					*)
	(*							*)
	(*	Status:	Seems to be working.			*)
	(*							*)
	(********************************************************)

FROM Semaphores IMPORT
    (* type *)	Semaphore;

PROCEDURE Sleep (milliseconds: CARDINAL);

    (* Puts the caller to sleep for approximately the given number of	*)
    (* milliseconds.  The time is not guaranteed to be precise, because	*)
    (* (a) after the specified time has expired, the caller is made	*)
    (* ready, but will not run immediately unless it has a higher	*)
    (* priority than the task which is running at that time, and (b) we	*)
    (* do not necessarily run the hardware timer with millisecond	*)
    (* resolution anyway.  High resolution just adds to the system	*)
    (* overhead created by the timer interrupts.  For an application	*)
    (* which genuinely needs high-precision delays, it makes more sense	*)
    (* to have a separate hardware timer dedicated just to that job.	*)

PROCEDURE TimedWait (VAR (*INOUT*) s: Semaphore;  TimeLimit: INTEGER;
					VAR (*OUT*) TimedOut: BOOLEAN);

    (* Like a semaphore Wait, except that it returns with TimedOut TRUE	*)
    (* if the corresponding Signal does not occur within TimeLimit	*)
    (* milliseconds.							*)

END Timer.