1.cons_init()

cons_init()->kbd_init()-> kbd_intr()+pic_enable(IRQ_KBD);

kbd_intr()->cons_intr(kbd_proc_data);//mainly init the buffer

keypoint is: pic_enable(IRQ_KBD) -- enable the keyboard interrupt

2. pic_init --- make 8259 work

3. idt_init() in trap.c to initialize IDT

void idt_init(void) { 
    extern uintptr_t __vectors[];
    for(int i=0; i<sizeof(idt)/sizeof(struct gatedesc);i++)
        SETGATE(idt[i], 0, GD_KTEXT, __vectors[i], DPL_KERNEL);

    // load the IDT
    lidt(&idt_pd);
}

4. enable INT

void intr_enable(void) { sti(); }
void intr_disable(void) { cli(); }

when there is an interrupt occurred, here are some steps:

a. vectors.S means IDT (number=256)

# handler
.text
.global __alltraps
.global vector0
vector0:
  pushl $0
  pushl $0
  jmp __alltraps
.global vector1
vector1:
  pushl $0
  pushl $1
  jmp __alltraps
  ...

it will jmp to __alltraps which is in trapentry.S

b. trapentry.S

#include <memlayout.h>

# vectors.S sends all traps here.
.text
.globl __alltraps
__alltraps:
    # push registers to build a trap frame
    # therefore make the stack look like a struct trapframe
    pushl %ds
    pushl %es
    pushal

    # load GD_KDATA into %ds and %es to set up data segments for kernel
    movl $GD_KDATA, %eax
    movw %ax, %ds
    movw %ax, %es

    # push %esp to pass a pointer to the trapframe as an argument to trap()
    pushl %esp

    # call trap(tf), where tf=%esp
    call trap

    # pop the pushed stack pointer
    popl %esp

    # return falls through to trapret...
.globl __trapret
__trapret:
    # restore registers from stack
    popal

    # restore %ds and %es
    popl %es
    popl %ds

    # get rid of the trap number and error code
    addl $0x8, %esp
    iret

then it will call trap() in trap.c

c. trap.c

static void trap_dispatch(struct trapframe *tf) {
    char c;
    switch(tf->tf_trapno) {
        case IRQ_OFFSET + IRQ_KBD:
            c = cons_getc();
            cprintf("%s [%03d] %c\n", (tf->tf_trapno != IRQ_OFFSET + IRQ_KBD) ? "serial":"kbd", c, c);
            keybuf_push(&kb, c);
            break;
        default:
            cprintf("UNKNOW INT\n");
    }
    cprintf("time to return\n");
}

void trap(struct trapframe *tf) {
    trap_dispatch(tf);
}

the (popl %esp) make it possible that the PC can return to the break point