Re: Access to IO registers from user-space in recent Linux versions

["J. Lewis Muir" <jlmuir@anl.gov>]

On 7/9/09 1:08 PM, 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
> (mockbuild@x86-4.fedora.phx.redhat.com)
>
> (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?

Hi, Mark.

Is the iopl(3) call succeeding?  FYI, I noticed in dxp version 2-9 in
line 893 of dxpApp/src/drvDxp.c, the return status of the iopl(3) call
is not checked.

Also, some instructional documents I've read said, if using GCC, one
must compile with the -O option (?).

Lewis