6 static volatile uint64_t ticks;
9 irq20_timer (struct intr_args *args UNUSED)
12 intr_yield_on_return ();
15 /* Sets up the 8254 Programmable Interrupt Timer (PIT) to
16 interrupt PIT_FREQ times per second, and registers the
17 corresponding interrupt. */
21 /* 8254 input frequency divided by TIMER_FREQ, rounded to
23 uint16_t count = (1193180 + TIMER_FREQ / 2) / TIMER_FREQ;
25 outb (0x43, 0x34); /* CW: counter 0, LSB then MSB, mode 2, binary. */
26 outb (0x40, count & 0xff);
27 outb (0x40, count >> 8);
29 intr_register (0x20, 0, IF_OFF, irq20_timer);
35 enum if_level old_level = intr_disable ();
37 intr_set_level (old_level);
42 timer_elapsed (uint64_t then)
44 uint64_t now = timer_ticks ();
45 return now > then ? now - then : ((uint64_t) -1 - then) + now + 1;
48 /* Suspends execution for at least DURATION ticks. */
50 timer_wait_until (uint64_t duration)