一个getchar函数的实现！

struct tty_queue {
    long head;
    long tail;
    char buf[64];
}read_q = { 0,0,""} ;

static int in = 0;

long volatile timerc;

 

 

 

void printf(char *fmt, ...)
{
    __asm__ __volatile__ (
            "movl $7, %%eax\n\t"
            "int $0x80\n\t"
            ::"b" (fmt)
            );
}

void delay(void)
{
      int time_delay;
      time_delay = timerc;
      while((timerc - time_delay ) < 6);
}

unsigned char getchar(void)
{ 
 unsigned char ch;

 if(read_q.tail == read_q.head)

{ 
  while(input == 0 ) {
   delay();
  }
  in = 0 ;
 }
 
 ch = read_q.buf[read_q.tail];
 read_q.tail = (read_q.tail + 1) & (64 - 1);

 return ch;
}
int main()
{
 char a;
 a=getchar();
 printf("1jjk give you a message !the char is %c\n", a);
}

 

$gcc a.c

$./a.out