有了《初识Linux汇编》和《内联汇编控制PC蜂鸣器》两篇文章的基础了解后,我们使用内联汇编来改造《C编程控制PC蜂鸣器》一文的例子,最终的代码如下:
#include <stdio.h>
#include <unistd.h>
#include <sys/io.h>
/* The clock frequency of the i8253/i8254 PIT */
#define PIT_TICK_RATE 1193182ul
void beep(unsigned int value)
{
unsigned int count = 0;
unsigned char val;
unsigned short port;
if (value > 20 && value < 32767)
count = PIT_TICK_RATE / value;
iopl(3);
if (count) {
val = 0xB6;
port = 0x43;
asm volatile("outb %0,%1" : : "a" (val), "dN" (port));
val = count & 0xff;
port = 0x42;
asm volatile("outb %0,%1" : : "a" (val), "dN" (port));
val = (count >> 8) & 0xff;
asm volatile("outb %0,%1" : : "a" (val), "dN" (port));
port = 0x61;
asm volatile("inb %1,%0" : "=a" (val) : "dN" (port));
val = val | 3;
asm volatile("outb %0,%1" : : "a" (val), "dN" (port));
} else {
port = 0x61;
asm volatile("inb %1,%0" : "=a" (val) : "dN" (port));
val = val & 0xFC;
asm volatile("outb %0,%1" : : "a" (val), "dN" (port));
}
iopl(0);
}
int main(int argc,char * argv[])
{
unsigned int val;
if (argc != 2) {
printf("Usage:%s value\n 20<value<32767,other value will stop!\n",argv[0]);
return 0;
}
val = atoi(argv[1]);
beep(val);
return 0;
}
对于相应的Makefile文件及C源码文件名均未更改,本次仅作8254控制部分的更改,其他均保留。