Make sure loops_per_tick doesn't overflow to zero.

[pintos-anon] / src / devices / timer.c

diff --git a/src/devices/timer.c b/src/devices/timer.c
index 9e1b4989c833b62cfcaa5a66032c1cae1124fec0..662e0c6f5645be139fde64f9f300bcd0f17d9c52 100644 (file)
--- a/src/devices/timer.c
+++ b/src/devices/timer.c
@@ -16,9 +16,6 @@
 #error TIMER_FREQ <= 1000 recommended
 #endif
 
-/* Number of time ticks to elapse between process yields. */
-#define TIME_SLICE 1
-
 /* Number of timer ticks since OS booted. */
 static volatile int64_t ticks;
 
@@ -45,7 +42,7 @@ timer_init (void)
   outb (0x40, count & 0xff);
   outb (0x40, count >> 8);
 
-  intr_register (0x20, 0, INTR_OFF, timer_interrupt, "8254 Timer");
+  intr_register_ext (0x20, timer_interrupt, "8254 Timer");
 }
 
 /* Calibrates loops_per_tick, used to implement brief delays. */
@@ -60,8 +57,11 @@ timer_calibrate (void)
   /* Approximate loops_per_tick as the largest power-of-two
      still less than one timer tick. */
   loops_per_tick = 1u << 10;
-  while (!too_many_loops (loops_per_tick << 1))
-    loops_per_tick <<= 1;
+  while (!too_many_loops (loops_per_tick << 1)) 
+    {
+      loops_per_tick <<= 1;
+      ASSERT (loops_per_tick != 0);
+    }
 
   /* Refine the next 8 bits of loops_per_tick. */
   high_bit = loops_per_tick;
@@ -126,7 +126,7 @@ timer_nsleep (int64_t ns)
 void
 timer_print_stats (void) 
 {
-  printf ("Timer: %"PRId64" ticks\n", ticks);
+  printf ("Timer: %"PRId64" ticks\n", timer_ticks ());
 }
 \f
 /* Timer interrupt handler. */
@@ -135,8 +135,6 @@ timer_interrupt (struct intr_frame *args UNUSED)
 {
   ticks++;
   thread_tick ();
-  if (ticks % TIME_SLICE == 0)
-    intr_yield_on_return ();
 }
 
 /* Returns true if LOOPS iterations waits for more than one timer
@@ -167,7 +165,7 @@ too_many_loops (unsigned loops)
    differently in different places the results would be difficult
    to predict. */
 static void NO_INLINE
-busy_wait (int64_t loops) 
+busy_wait (volatile int64_t loops) 
 {
   while (loops-- > 0)
     continue;