challenge6.3:interrupt clock

完善trap.c中的中断处理函数trap，在对时钟中断进行处理的部分填写trap函数中处理时钟中断的部分，使操作系统每遇到100次时钟中断后，调用print_ticks子程序，向屏幕上打印一行文字”100 ticks”。

先看一下print_ticks子程序；

#define TICK_NUM 100
static void print_ticks()
{
    cprintf("%d ticks\n", TICK_NUM);   // 打印了TICK_NUM变量
#ifdef DEBUG_GRADE
    cprintf("End of Test.\n");
    panic("EOT: kernel seems ok.");
#endif
}

再看一下kern/driver/clock.c：

#include <x86.h>
#include <trap.h>
#include <stdio.h>
#include <picirq.h>

/* *
 * Support for time-related hardware gadgets - the 8253 timer,
 * which generates interruptes on IRQ-0.
 * */

#define IO_TIMER1           0x040               // 8253 Timer #1

/* *
 * 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_MODE      (IO_TIMER1 + 3)         // timer mode port
#define TIMER_SEL0      0x00                    // select counter 0
#define TIMER_RATEGEN   0x04                    // mode 2, rate generator
#define TIMER_16BIT     0x30                    // r/w counter 16 bits, LSB first

volatile size_t ticks;

/* *
 * clock_init - initialize 8253 clock to interrupt 100 times per second,
 * and then enable IRQ_TIMER.
 * */
void
clock_init(void) {
    // set 8253 timer-chip
    outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
    outb(IO_TIMER1, TIMER_DIV(100) % 256);
    outb(IO_TIMER1, TIMER_DIV(100) / 256);

    // initialize time counter 'ticks' to zero
    ticks = 0;

    cprintf("++ setup timer interrupts\n");
    pic_enable(IRQ_TIMER);
}

可以看到，在clock_init()中里定义了ticks，根据要求，当ticks每次+1，直到100时即调用print_ticks()函数打印信息；

于是填充代码，在kern/trap/trap.c中有：

/* trap_dispatch - dispatch based on what type of trap occurred */
static void
trap_dispatch(struct trapframe *tf)
{
    char c;

    switch (tf->tf_trapno)
    {
    case IRQ_OFFSET + IRQ_TIMER:
        /* LAB1 YOUR CODE : STEP 3 */
        /* handle the timer interrupt */
        /* (1) After a timer interrupt, you should record this event using a global variable (increase it), such as ticks in kern/driver/clock.c
         * (2) Every TICK_NUM cycle, you can print some info using a funciton, such as print_ticks().
         * (3) Too Simple? Yes, I think so!
         */
        ticks++;
        while(ticks % 100 == 0)         // 100也可以用已经定义的TICK_NUM来替换
            print_ticks();
        break;
        break;
    case IRQ_OFFSET + IRQ_COM1:
        c = cons_getc();
        cprintf("serial [%03d] %c\n", c, c);
        break;
    case IRQ_OFFSET + IRQ_KBD:
        c = cons_getc();
        cprintf("kbd [%03d] %c\n", c, c);
        break;
    //LAB1 CHALLENGE 1 : YOUR CODE you should modify below codes.
    case T_SWITCH_TOU:
    case T_SWITCH_TOK:
        panic("T_SWITCH_** ??\n");
        break;
    case IRQ_OFFSET + IRQ_IDE1:
    case IRQ_OFFSET + IRQ_IDE2:
        /* do nothing */
        break;
    default:
        // in kernel, it must be a mistake
        if ((tf->tf_cs & 3) == 0)
        {
            print_trapframe(tf);
            panic("unexpected trap in kernel.\n");
        }
    }
}

/* *
 * trap - handles or dispatches an exception/interrupt. if and when trap() returns,
 * the code in kern/trap/trapentry.S restores the old CPU state saved in the
 * trapframe and then uses the iret instruction to return from the exception.
 * */
void trap(struct trapframe *tf)
{
    // dispatch based on what type of trap occurred
    trap_dispatch(tf);
}

make qemu查看结果；

...
100 ticks
100 ticks
100 ticks
100 ticks
100 ticks
100 ticks
100 ticks
100 ticks
...