kernel/timer.c

   1 #include "timer.h"
   2 #include "portio.h"
   3 #include "console.h"
   4 #include "interrupt.h"
   5 #include "stdint.h"
   6 #include "general.h"
   7 #include "critical.h"
   8 #include "task.h"
   9
  10 #define TIMER_IRQ 0      // the IRQ the PIT is connected to
  11 #define TIMER_FREQ 1000  // frequency to set the timer to
  12 #define CTL 0x43         // control register
  13 #define CNT0 0x40        // count register 0
  14 #define CNT1 0x41        // count register 1
  15 #define CNT2 0x42        // count register 2
  16
  17 static tick_t tick = 0;    // current tick number
  18 static unsigned long freq; // current timer frequency
  19
  20 tick_t get_tick(void)
  21 {
  22     return tick;
  23 }
  24
  25 static void timer_interrupt(int vector, struct interrupt_stack *is)
  26 {
  27     tick++;
  28     ack_irq(TIMER_IRQ);
  29
  30     if(!(tick % 20))
  31     {if(MULTITASKING){switch_task(is);}}
  32 }
  33
  34 void set_frequency(unsigned long new_freq)
  35 {
  36     unsigned short divisor;
  37     divisor = 1193180 / new_freq;
  38     freq = (1193180LL << 32) / divisor;
  39     outb(CTL, 0x36);
  40     outb(CNT0, divisor);
  41     outb(CNT0, divisor >> 8);
  42 }
  43
  44 // timer initialization
  45 void timer_init(void)
  46 {
  47     unsigned char p61h;
  48     // Timer's base frequency is 1,193,180 Hz
  49     // We set the frequency divider to get
  50     // TIMER_FREQ Hz output
  51     outb(CTL, 0x54);
  52     outb(CNT1, 18); // LSB only clock divisor (?)
  53     tick = 0;
  54     interrupt_set_handler(irq_to_int(TIMER_IRQ), timer_interrupt);
  55     set_frequency(TIMER_FREQ);
  56     unmask_irq(TIMER_IRQ);
  57
  58     outb(CTL, 0xB6);
  59     outb(CNT2, 54);
  60     outb(CNT2, 124);
  61     p61h = inb(0x61);
  62     p61h |= 3;
  63     outb(0x61, p61h);
  64 }
  65
  66 uint64_t read_cpu_timestamp(void)
  67 {
  68     uint32_t hi, lo;
  69     __asm__ __volatile__("rdtsc;":"=d"(hi),"=a"(lo)::"memory");
  70     return (uint64_t)(((uint64_t)hi << 32) | lo);
  71 }
  72