inb_p函数的理解

inb_p通过port端口读取数据，并延迟

#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; \

})

比较容易理解的代码如下：

#define inb_p(port) _inb_p((unsigned short)(port))

_inline unsigned char _inb_p(unsigned short port)

{

//   volatile unsigned char _v;

     _asm {

         mov dx,port

         in al,dx

//       mov _v,al

         jmp l1

     l1: jmp l2

     l2:

     }

//   return _v;

}

汇编的in从dx端口读一个字节数据到al