I am trying to understand the following code:
#include<stdio.h>
#include<stdlib.h>
#include<sys/io.h>
#define baseport 0x378
int main()
{
int b;
if(ioperm(baseport,3,1))
{
perror("ioperm");
exit(1);
}
outb(0,baseport);
usleep(1000000);
printf("\n the status: %x,\n",inb(baseport));
if (ioperm(baseport,3,0)) {perror("ioperm"); exit(1);}
exit(0);
}
The output is 0xff, 255 in decimal, whether I write on Port 1 or Port 0 (using outb()
). I cannot understand why it is 255 when I am writing 0 to it.
The result of doing inb(0x378) is hardware-dependent. Some chips return the value you have written previously with outb, and some other chips just return garbage. In any case, it is not the port to read bytes from a potentially connected device.