为啥这个用IDE技术读取不成功?

代码是multiboot自制内核的一部分,如下:
经过测试,在读取双字节时都是0，而读取的内容实际上不全是0,是啥问题呢?

```c
#define IDE_READ_MAX_SECRORS    256

#define IDE_READ_READNUM_PORT   0x1f2
#define IDE_READ_LBA_PORTA      0x1f3
#define IDE_READ_LBA_PORTB      0x1f4
#define IDE_READ_LBA_PORTC      0x1f5
#define IDE_READ_LBA_PORTD      0x1f6
#define IDE_READ_DEVICE_PORT    0x1f6
#define IDE_READ_MODE_PORT      0x1f6
#define IDE_FUN_MODE            0x1f7
#define IDE_FUN_MODE_READ       0x20
#define IDE_STAGE_PORT          0x1f7
#define IDE_READ_DATA_PORT      0x1f0

unsigned char readSectors(unsigned char * buf,
                         unsigned int device, 
                         unsigned long lba, 
                         unsigned char numOfSectors){
  outb(IDE_READ_READNUM_PORT,numOfSectors);
  outb(IDE_READ_LBA_PORTA,lba);
  outb(IDE_READ_LBA_PORTB,lba>>8);
  outb(IDE_READ_LBA_PORTC,(lba>>16)&0xff);
  outb(IDE_READ_LBA_PORTD,0xe0|(device<<4));
  
  outb(IDE_FUN_MODE,IDE_FUN_MODE_READ);
  char stat = 0;
  int a = 0;
  while(((stat&(1<<4))>>4)!=1)
    stat = inb(IDE_STAGE_PORT);
  unsigned short i;
  for(i=0;i<numOfSectors*512;i+=2)
  {
    short wordData = inw(IDE_READ_DATA_PORT);
    buf[i] = wordData & 0xff;
    buf[i+1] = wordData >> 8;
  }
  return numOfSectors;
}

io.h 的部分:

#ifndef _IO_H
#define _IO_H

#define outb(value,port) \
__asm__ ("outb %%al,%%dx"::"a" (value),"d" (port))


#define inb(port) ({ \
unsigned char _v; \
__asm__ volatile ("inb %%dx,%%al":"=a" (_v):"d" (port)); \
_v; \
})

#define outb_p(value,port) \
__asm__ ("outb %%al,%%dx\n" \
        "\tjmp 1f\n" \
        "1:\tjmp 1f\n" \
        "1:"::"a" (value),"d" (port))

#define inb_p(port) ({ \
unsigned char _v; \
__asm__ volatile ("inb %%dx,%%al\n" \
    "\tjmp 1f\n" \
    "1:\tjmp 1f\n" \
    "1:":"=a" (_v):"d" (port)); \
_v; \
})

static __inline void
outw (unsigned short int __value, unsigned short int __port)
{
  __asm__ __volatile__ ("outw %w0,%w1": :"a" (__value), "Nd" (__port));

}

static __inline unsigned short int
inw (unsigned short int __port)
{
  unsigned short _v;

  __asm__ __volatile__ ("inw %w1,%0":"=a" (_v):"Nd" (__port));
  return _v;
}

#define NULL -1

#endif

```