-#include "timer.h"
-#include "lib/debug.h"
+#include "devices/timer.h"
+#include <debug.h>
+#include <inttypes.h>
+#include <round.h>
+#include <stdio.h>
#include "threads/interrupt.h"
#include "threads/io.h"
+#include "threads/synch.h"
+#include "threads/thread.h"
+/* See [8254] for hardware details of the 8254 timer chip. */
+
#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 since OS booted. */
-static volatile int64_t ticks;
+static int64_t ticks;
+
+/* Number of loops per timer tick.
+ Initialized by timer_calibrate(). */
+static unsigned loops_per_tick;
static intr_handler_func timer_interrupt;
+static bool too_many_loops (unsigned loops);
+static void busy_wait (int64_t loops);
+static void real_time_sleep (int64_t num, int32_t denom);
+static void real_time_delay (int64_t num, int32_t denom);
-/* 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
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. */
+void
+timer_calibrate (void)
+{
+ unsigned high_bit, test_bit;
+
+ ASSERT (intr_get_level () == INTR_ON);
+ printf ("Calibrating timer... ");
+
+ /* 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;
+ ASSERT (loops_per_tick != 0);
+ }
+
+ /* Refine the next 8 bits of loops_per_tick. */
+ high_bit = loops_per_tick;
+ for (test_bit = high_bit >> 1; test_bit != high_bit >> 10; test_bit >>= 1)
+ if (!too_many_loops (high_bit | test_bit))
+ loops_per_tick |= test_bit;
+
+ printf ("%'"PRIu64" loops/s.\n", (uint64_t) loops_per_tick * TIMER_FREQ);
}
/* Returns the number of timer ticks since the OS booted. */
enum intr_level old_level = intr_disable ();
int64_t t = ticks;
intr_set_level (old_level);
+ barrier ();
return t;
}
return timer_ticks () - then;
}
-/* Suspends execution for approximately MS milliseconds. */
+/* Sleeps for approximately TICKS timer ticks. Interrupts must
+ be turned on. */
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 ();
+ ASSERT (intr_get_level () == INTR_ON);
while (timer_elapsed (start) < ticks)
- continue;
+ thread_yield ();
}
-/* Suspends execution for approximately US microseconds.
- Note: this is ridiculously inaccurate. */
+/* Sleeps for approximately MS milliseconds. Interrupts must be
+ turned on. */
+void
+timer_msleep (int64_t ms)
+{
+ real_time_sleep (ms, 1000);
+}
+
+/* Sleeps for approximately US microseconds. Interrupts must be
+ turned on. */
void
timer_usleep (int64_t us)
{
- timer_msleep (us / 1000 + 1);
+ real_time_sleep (us, 1000 * 1000);
}
-/* Suspends execution for approximately NS nanoseconds.
- Note: this is ridiculously inaccurate. */
+/* Sleeps for approximately NS nanoseconds. Interrupts must be
+ turned on. */
void
timer_nsleep (int64_t ns)
{
- timer_msleep (ns / 1000000 + 1);
+ real_time_sleep (ns, 1000 * 1000 * 1000);
+}
+
+/* Busy-waits for approximately MS milliseconds. Interrupts need
+ not be turned on.
+
+ Busy waiting wastes CPU cycles, and busy waiting with
+ interrupts off for the interval between timer ticks or longer
+ will cause timer ticks to be lost. Thus, use timer_msleep()
+ instead if interrupts are enabled. */
+void
+timer_mdelay (int64_t ms)
+{
+ real_time_delay (ms, 1000);
+}
+
+/* Sleeps for approximately US microseconds. Interrupts need not
+ be turned on.
+
+ Busy waiting wastes CPU cycles, and busy waiting with
+ interrupts off for the interval between timer ticks or longer
+ will cause timer ticks to be lost. Thus, use timer_usleep()
+ instead if interrupts are enabled. */
+void
+timer_udelay (int64_t us)
+{
+ real_time_delay (us, 1000 * 1000);
+}
+
+/* Sleeps execution for approximately NS nanoseconds. Interrupts
+ need not be turned on.
+
+ Busy waiting wastes CPU cycles, and busy waiting with
+ interrupts off for the interval between timer ticks or longer
+ will cause timer ticks to be lost. Thus, use timer_nsleep()
+ instead if interrupts are enabled.*/
+void
+timer_ndelay (int64_t ns)
+{
+ real_time_delay (ns, 1000 * 1000 * 1000);
+}
+
+/* Prints timer statistics. */
+void
+timer_print_stats (void)
+{
+ printf ("Timer: %"PRId64" ticks\n", timer_ticks ());
}
\f
/* Timer interrupt handler. */
timer_interrupt (struct intr_frame *args UNUSED)
{
ticks++;
- intr_yield_on_return ();
+ thread_tick ();
+}
+
+/* Returns true if LOOPS iterations waits for more than one timer
+ tick, otherwise false. */
+static bool
+too_many_loops (unsigned loops)
+{
+ /* Wait for a timer tick. */
+ int64_t start = ticks;
+ while (ticks == start)
+ barrier ();
+
+ /* Run LOOPS loops. */
+ start = ticks;
+ busy_wait (loops);
+
+ /* If the tick count changed, we iterated too long. */
+ barrier ();
+ return start != ticks;
+}
+
+/* Iterates through a simple loop LOOPS times, for implementing
+ brief delays.
+
+ Marked NO_INLINE because code alignment can significantly
+ affect timings, so that if this function was inlined
+ differently in different places the results would be difficult
+ to predict. */
+static void NO_INLINE
+busy_wait (int64_t loops)
+{
+ while (loops-- > 0)
+ barrier ();
+}
+
+/* Sleep for approximately NUM/DENOM seconds. */
+static void
+real_time_sleep (int64_t num, int32_t denom)
+{
+ /* Convert NUM/DENOM seconds into timer ticks, rounding down.
+
+ (NUM / DENOM) s
+ ---------------------- = NUM * TIMER_FREQ / DENOM ticks.
+ 1 s / TIMER_FREQ ticks
+ */
+ int64_t ticks = num * TIMER_FREQ / denom;
+
+ ASSERT (intr_get_level () == INTR_ON);
+ if (ticks > 0)
+ {
+ /* We're waiting for at least one full timer tick. Use
+ timer_sleep() because it will yield the CPU to other
+ processes. */
+ timer_sleep (ticks);
+ }
+ else
+ {
+ /* Otherwise, use a busy-wait loop for more accurate
+ sub-tick timing. */
+ real_time_delay (num, denom);
+ }
+}
+
+/* Busy-wait for approximately NUM/DENOM seconds. */
+static void
+real_time_delay (int64_t num, int32_t denom)
+{
+ /* Scale the numerator and denominator down by 1000 to avoid
+ the possibility of overflow. */
+ ASSERT (denom % 1000 == 0);
+ busy_wait (loops_per_tick * num / 1000 * TIMER_FREQ / (denom / 1000));
}
projects / pintos-anon / blobdiff