init: init nachos hw01, should pass jenkins os_group_20_hw job but fail on os_group_20_ta job

code/threads/alarm.cc

@@ -0,0 +1,55 @@
+// alarm.cc
+//	Routines to use a hardware timer device to provide a
+//	software alarm clock.  For now, we just provide time-slicing.
+//
+//	Not completely implemented.
+//
+// Copyright (c) 1992-1996 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+
+#include "copyright.h"
+#include "alarm.h"
+#include "main.h"
+
+//----------------------------------------------------------------------
+// Alarm::Alarm
+//      Initialize a software alarm clock.  Start up a timer device
+//
+//      "doRandom" -- if true, arrange for the hardware interrupts to 
+//		occur at random, instead of fixed, intervals.
+//----------------------------------------------------------------------
+
+Alarm::Alarm(bool doRandom)
+{
+    timer = new Timer(doRandom, this);
+}
+
+//----------------------------------------------------------------------
+// Alarm::CallBack
+//	Software interrupt handler for the timer device. The timer device is
+//	set up to interrupt the CPU periodically (once every TimerTicks).
+//	This routine is called each time there is a timer interrupt,
+//	with interrupts disabled.
+//
+//	Note that instead of calling Yield() directly (which would
+//	suspend the interrupt handler, not the interrupted thread
+//	which is what we wanted to context switch), we set a flag
+//	so that once the interrupt handler is done, it will appear as 
+//	if the interrupted thread called Yield at the point it is 
+//	was interrupted.
+//
+//	For now, just provide time-slicing.  Only need to time slice 
+//      if we're currently running something (in other words, not idle).
+//----------------------------------------------------------------------
+
+void 
+Alarm::CallBack() 
+{
+    Interrupt *interrupt = kernel->interrupt;
+    MachineStatus status = interrupt->getStatus();
+    
+    if (status != IdleMode) {
+	interrupt->YieldOnReturn();
+    }
+}