X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fdevices%2Ftimer.c;h=9c611a1d3eda68b6fd2317304faaef9381f9eb40;hb=231f9a0dc4528a081b0295d98d732d4de74a47b2;hp=85bc3ee33d3345fa519f6d3cbd80c1011aee01e1;hpb=f6580e9ad405b519dbe85027691bf3c66074b0a4;p=pintos-anon

diff --git a/src/devices/timer.c b/src/devices/timer.c
index 85bc3ee..9c611a1 100644
--- a/src/devices/timer.c
+++ b/src/devices/timer.c
@@ -1,18 +1,27 @@
-#include "timer.h"
-#include "lib/debug.h"
+#include "devices/timer.h"
+#include <debug.h>
+#include <round.h>
 #include "threads/interrupt.h"
 #include "threads/io.h"
+#include "threads/thread.h"
   
 #if TIMER_FREQ < 19
 #error 8254 timer requires TIMER_FREQ >= 19
 #endif
+#if TIMER_FREQ > 1000
+#error TIMER_FREQ <= 1000 recommended
+#endif
+
+/* Number of timer ticks that a process gets before being
+   preempted. */
+#define TIME_SLICE 1
 
 /* Number of timer ticks since OS booted. */
 static volatile int64_t ticks;
 
 static intr_handler_func timer_interrupt;
 
-/* Sets up the 8254 Programmable Interrupt Timer (PIT) to
+/* Sets up the 8254 Programmable Interval Timer (PIT) to
    interrupt PIT_FREQ times per second, and registers the
    corresponding interrupt. */
 void
@@ -47,31 +56,40 @@ timer_elapsed (int64_t then)
   return timer_ticks () - then;
 }
 
-/* Suspends execution for approximately MS milliseconds. */
+/* Suspends execution for approximately TICKS timer ticks. */
 void
-timer_msleep (int64_t ms) 
+timer_sleep (int64_t ticks) 
 {
-  int64_t ticks = (int64_t) ms * TIMER_FREQ / 1000;
   int64_t start = timer_ticks ();
 
   while (timer_elapsed (start) < ticks) 
-    continue;
+    if (intr_get_level () == INTR_ON)
+      thread_yield ();
 }
 
-/* Suspends execution for approximately US microseconds.
-   Note: this is ridiculously inaccurate. */
-void
-timer_usleep (int64_t us) 
+/* Returns MS milliseconds in timer ticks, rounding up. */
+int64_t
+timer_ms2ticks (int64_t ms) 
 {
-  timer_msleep (us / 1000 + 1);
+  /*       MS / 1000 s          
+     ------------------------ = MS * TIMER_FREQ / 1000 ticks. 
+     (1 / TIMER_FREQ) ticks/s
+  */
+  return DIV_ROUND_UP (ms * TIMER_FREQ, 1000);
 }
 
-/* Suspends execution for approximately NS nanoseconds.
-   Note: this is ridiculously inaccurate. */
-void
-timer_nsleep (int64_t ns) 
+/* Returns US microseconds in timer ticks, rounding up. */
+int64_t
+timer_us2ticks (int64_t us) 
+{
+  return DIV_ROUND_UP (us * TIMER_FREQ, 1000000);
+}
+
+/* Returns NS nanoseconds in timer ticks, rounding up. */
+int64_t
+timer_ns2ticks (int64_t ns) 
 {
-  timer_msleep (ns / 1000000 + 1);
+  return DIV_ROUND_UP (ns * TIMER_FREQ, 1000000000);
 }
 
 /* Timer interrupt handler. */
@@ -79,5 +97,6 @@ static void
 timer_interrupt (struct intr_frame *args UNUSED)
 {
   ticks++;
-  intr_yield_on_return ();
+  if (ticks % TIME_SLICE == 0)
+    intr_yield_on_return ();
 }