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Subject: Re: Access to IO registers from user-space in recent Linux versions
From: Till Straumann <[email protected]>
To: Mark Rivers <[email protected]>
Cc: [email protected], tech-talk <[email protected]>
Date: Thu, 09 Jul 2009 14:05:42 -0500
The iopl(3) followed by 'in' works fine for me (both, when compiled -m32 or without)

till@tillbook:~/tmp$ uname -a
Linux tillbook 2.6.28-13-generic #45-Ubuntu SMP Tue Jun 30 22:12:12 UTC 2009 x86_64 GNU/Linux


#include <stdio.h>
#include <sys/io.h>

int main(int argc, char **argv)
{
unsigned char  v;
unsigned short p;

   if ( argc < 2 || 1 != sscanf(argv[1],"%hi",&p) ) {
       fprintf(stderr,"Usage: %s <port>\n",argv[0]);
       return 1;
   }

   if ( iopl(3) ) {
       perror("iopl");
       return 1;
   }

   asm volatile ( "inb %1,%0" : "=a" (v) : "d"(p));

   printf("0x%02x\n",v);
   return 0;
}

-- Till


Mark Rivers wrote:

Folks,

I have an EPICS application that directly accesses the parallel port (EPP) registers from user space on Linux. This is to communicate with an XIA Saturn spectroscopy module.

In order versions of Linux this worked fine if I ran the application as root, or by calling iopl(3) as root before exec-ing the EPICS application.

I am now trying to run this under a recent Linux (Redhat Fedora) version

baja:~>more /proc/version

Linux version 2.6.26.8-57.fc8 ([email protected])

(gcc version 4.1.2 20070925 (Red Hat 4.1.2-33))

#1 SMP Thu Dec 18 18:59:49 EST 2008

The EPICS IOC now crashes with a segmentation fault when trying to access the EPP port, even when running as root, and the following entry appears in /var/log/messages

Jul 9 11:43:44 baja kernel: dxpApp[27837] general protection ip:80a90a6 sp:ff8ea8ac error:0 in dxpApp[8048000+1f7000]

Does anyone know what one needs to do in recent Linux versions to get access to the IO registers from user-space?

Thanks,

Mark



Replies:
Re: Access to IO registers from user-space in recent Linux versions David Kline
RE: Access to IO registers from user-space in recent Linux versions Mark Rivers
References:
Access to IO registers from user-space in recent Linux versions Mark Rivers

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