Home / ubuntu / Questions / 22100
In Process
Renjith G
Asked: 2011-01-19 02:51:35 +0800 CST

Usage of inb, inl, inw to access kernel space from user space

  • 772

Could you please give me some user space examples of using inb, inl, inw to access kernel space in ubuntu?

/Kanu

drivers

2 Answers

  1. These functions (or macros) are defined in <asm/io.h>. You need to tell gcc to -Optimise the code for them to be inlined (I think).

    For their usage, type 

    man inw

    Makelinux.net also has a guide on how to use them.

    I can't give you an example since it depends on the hardware you're using, but this should get you started.

    If anyone is interested in it, there's also a Python module, portio, to provide the same functionality.

    • 1

  2. To use IO port commands (in/out), you need to run as root and have reserved access via the ioperm() call: http://manpages.ubuntu.com/ioperm

    If this is beep.c:

    /* Copyright 2011, Kees Cook <[email protected]>, License: GPLv2 */
#include <unistd.h>
#include <stdio.h>
#include <sys/io.h>

int main()
{
   unsigned char orig, bits;

   /* gain access to speaker control port */
   if (ioperm(0x61, 0x61, 1) < 0) {
       perror("0x61");
       return 1;
   }
   /* gain access to speaker frequency port */
   if (ioperm(0x42, 0x42, 1) < 0) {
       perror("0x42");
       return 2;
   }

   /* turn on speaker */
   orig = bits = inb(0x61);
   bits |= 3;
   outb(bits, 0x61);

   /* set 1000 Hz frequency */
   bits = 0xA9;
   outb(bits, 0x42);
   bits = 0x04;
   outb(bits, 0x42);

   /* listen to the beep */
   sleep(1);

   /* restore speaker bits to turn off speaker */
   outb(orig, 0x61);

   return 0;
}

    $ make beep

    $ sudo ./beep

    • 1