#include "types.h"#include "x86.h"#include "defs.h"#include "traps.h"// Register definitions for the Intel// 8253/8254/82C54 Programmable Interval Timer (PIT).#define IO_TIMER1       0x040           // 8253 Timer #1#define IO_TIMER2       0x048           // 8253 Timer #2 (EISA only)// Frequency of all three count-down timers; (TIMER_FREQ/freq) is the// appropriate count to generate a frequency of freq hz.#define TIMER_FREQ      1193182#define TIMER_DIV(x)    ((TIMER_FREQ+(x)/2)/(x))#define TIMER_CNTR0     (IO_TIMER1 + 0) // timer 0 counter port#define TIMER_CNTR1     (IO_TIMER1 + 1) // timer 1 counter port#define TIMER_CNTR2     (IO_TIMER1 + 2) // timer 2 counter port#define TIMER_MODE      (IO_TIMER1 + 3) // timer mode port#define TIMER_SEL0      0x00    // select counter 0#define TIMER_SEL1      0x40    // select counter 1#define TIMER_SEL2      0x80    // select counter 2#define TIMER_INTTC     0x00    // mode 0, intr on terminal cnt#define TIMER_ONESHOT   0x02    // mode 1, one shot#define TIMER_RATEGEN   0x04    // mode 2, rate generator#define TIMER_SQWAVE    0x06    // mode 3, square wave#define TIMER_SWSTROBE  0x08    // mode 4, s/w triggered strobe#define TIMER_HWSTROBE  0x0a    // mode 5, h/w triggered strobe#define TIMER_LATCH     0x00    // latch counter for reading#define TIMER_LSB       0x10    // r/w counter LSB#define TIMER_MSB       0x20    // r/w counter MSB#define TIMER_16BIT     0x30    // r/w counter 16 bits, LSB first#define TIMER_BCD       0x01    // count in BCDvoidpit8253_timerinit(void){  // initialize 8253 clock to interrupt 100 times/sec  outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);  outb(IO_TIMER1, TIMER_DIV(100) % 256);  outb(IO_TIMER1, TIMER_DIV(100) / 256);  irq_enable(IRQ_TIMER);}