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From: "Franz Hollerer" <eeg@telecom.at>
To: kuku@gilberto.physik.rwth-aachen.de, Gabor Zahemszky <zgabor@CoDe.hu>
Date:          Tue, 23 Apr 1996 01:01:43 +0000
Subject:       Re: How can I read/write from/to an I/O-port?
CC: freebsd-questions@freebsd.org
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> > > I have a little problem. So I hope someone can help
> > > me:
> > >  
> > > Under Linux a /dev/port exits to write/read to/from an I/O-port.
> > > Does a similar /dev/??? exits under FreeBSD or must I write
> > > a little device driver for this?
> > 
> > Under FreeBSD there is /dev/io.
> > 
> > Do an open("/dev/io",flags,mode) on it and you can access i/o
> > ports using in/out instructions.
> 
> OK.  How?  What does flags mean?  How can I use the fd, I get from open?
> (A little example please....)

Hi,

I did not exactly understand why it works, but it works!
I have looked at the code too. 
It really seams that port-io will change (Linux like). 
So I give you the example for Linux and SCO too.
For SCO I wrote a little device driver which behaves like /dev/port
under Linux.
Please notice that the example is a fragment of a library.

Franz

/* ============================================================ */

 /*
   read /write from/to an io-port:  inp(), outp()
   22.04.96 Franz Hollerer
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#if defined FreeBSD
#  include <machine/cpufunc.h>
#endif
#include <fcntl.h>
#include "decl.h"

/* ============================================================ */

int  prnterr           PARAMS((const char *fmt, ...));
char *getprgname PARAMS(());

void   outp PARAMS((int addr, u_char b));
u_char inp  PARAMS(());
   
/* ============================================================ */


#if defined LINUX || defined SCO

/*
   output byte from port
*/
void outp(addr, b)              /* Linux || SCO */
int addr;
u_char b;
{
  static int fd=-1;

  if (fd==-1 && (fd=open("/dev/port", O_WRONLY))==-1)
  {
    prnterr("%s: cannot open '/dev/port'\n", getprgname());
    exit(1);
  }
  lseek(fd, addr, SEEK_SET);
  write(fd, &b, 1);
}              /* eof outp */

#endif /* LINUX */


#if defined FreeBSD

/*
   output byte from port
*/
void outp(addr, b)              /* FreeBSD */
int addr;
u_char b;
{
  static int fd=-1;

  if (fd==-1 && (fd=open("/dev/io", O_WRONLY))==-1)
  {
    prnterr("%s: cannot open '/dev/io'\n", getprgname());
    exit(1);
  }
  outbv(addr, b);
}              /* eof outp */

#endif /* FreeBSD */


#if !defined LINUX && !defined FreeBSD && !defined SCO
#  warning "outp() not implemented!"
#endif /* !LINUX && !FreeBSD */

/* ============================================================ */

#if defined LINUX || SCO

/*
   input byte from port
*/
u_char inp(addr)               /* Linux || SCO */
int addr;
{
  static int fd=-1;
  u_char b;

  if (fd==-1 && (fd=open("/dev/port", O_RDONLY))==-1)
  {
    prnterr("%s: cannot open '/dev/port'\n", getprgname());
    exit(1);
  }
  lseek(fd, addr, SEEK_SET);
  read(fd, &b, 1);
  return(b);
}              /* eof inp */

#endif /* LINUX */

#if defined FreeBSD

/*
   input byte from port
*/
u_char inp(addr)               /* FreeBSD */
int addr;
{
  static int fd=-1;
  u_char b;

  if (fd==-1 && (fd=open("/dev/io", O_RDONLY))==-1)
  {
    prnterr("%s: cannot open '/dev/io'\n", getprgname());
    exit(1);
  }
  b=inbv(addr);
  return(b);
}              /* eof inp */

#endif /* FreeBSD */
 
#if !defined LINUX && !defined FreeBSD && !defined SCO
#  warning: "inp() not implemented!"
#endif /* !LINUX && !FreeBSD */

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