#include "timer.h"
#include "io.h"
#include "print.h"
#include "interrupt.h"
#include "thread.h"
#include "debug.h"

#define IRQ0_FREQUENCY	   100
#define INPUT_FREQUENCY	   1193180
#define COUNTER0_VALUE	   INPUT_FREQUENCY / IRQ0_FREQUENCY
#define CONTRER0_PORT	   0x40
#define COUNTER0_NO	   0
#define COUNTER_MODE	   2
#define READ_WRITE_LATCH   3
#define PIT_CONTROL_PORT   0x43

uint32_t ticks;          // ticks是内核自中断开启以来总共的嘀嗒数

/* 把操作的计数器counter_no、读写锁属性rwl、计数器模式counter_mode写入模式控制寄存器并赋予初始值counter_value */
static void frequency_set(uint8_t counter_port, \
			  uint8_t counter_no, \
			  uint8_t rwl, \
			  uint8_t counter_mode, \
			  uint16_t counter_value) {
/* 往控制字寄存器端口0x43中写入控制字 */
   outb(PIT_CONTROL_PORT, (uint8_t)(counter_no << 6 | rwl << 4 | counter_mode << 1));
/* 先写入counter_value的低8位 */
   outb(counter_port, (uint8_t)counter_value);
/* 再写入counter_value的高8位 */
   outb(counter_port, (uint8_t)counter_value >> 8);
}

/* 时钟的中断处理函数 */
static void intr_timer_handler(void) {
   struct task_struct* cur_thread = running_thread();

   ASSERT(cur_thread->stack_magic == 0x19870916);         // 检查栈是否溢出

   cur_thread->elapsed_ticks++;	  // 记录此线程占用的cpu时间嘀
   ticks++;	  //从内核第一次处理时间中断后开始至今的滴哒数,内核态和用户态总共的嘀哒数

   if (cur_thread->ticks == 0) {	  // 若进程时间片用完就开始调度新的进程上cpu
      schedule(); 
   } else {				  // 将当前进程的时间片-1
      cur_thread->ticks--;
   }
}

/* 初始化PIT8253 */
void timer_init() {
   put_str("timer_init start\n");
   /* 设置8253的定时周期,也就是发中断的周期 */
   frequency_set(CONTRER0_PORT, COUNTER0_NO, READ_WRITE_LATCH, COUNTER_MODE, COUNTER0_VALUE);
   register_handler(0x20, intr_timer_handler);
   put_str("timer_init done\n");
}