On Thu, 24 Dec 1998, Phil Daly wrote:
>
> I am trying to get shared memory to work but as soon as I access it from the
> real-time side, I get a major crash. I have followed the procedure in the
> HOWTO with my own structures. The line that offends is
>
> rtl_mptr->apdData[0].rawData[0] = 1;
>
> and the /var/log/messages file contains the illuminating information:
>
> Unable to handle kernel paging request at virtual address c1f00018
I struggled with this a while ago. The answer is that the HOWTO
is not currently up to date. The answer is in the following message,
poster to this list last July:
http://rtlinux.cs.nmt.edu/~rtlinux/rtl.w3archive/9807/msg00078.html
Here is the snippet you are looking for.
> Regarding the Shared Memory HOWTO discussion, I have found it impossible
> to get the:
> ... in an rt-module...
> char *rt_ptr = ADDRESS;
>
> technique to work. It results in a segmentation fault (Unable to handle
> paging request...) in all cases.
>
> By using:
> char *rt_ptr;
> rt_ptr = (char *)vremap(ADDRESS,LENGTH);
>
> ( and the appropriate vfree(rt_ptr) in the cleanup_module func)
>
>everything seems to work as expected.
If you want to see a relatively simple shared memory application
in action, visit my RTL demo program "BUZZ" at
http://mrb.niddk.nih.gov/butera/software/buzz.html
--
Rob Butera, Postdoctoral Fellow http://mrb.niddk.nih.gov/butera/
Laboratory for Neural Control, NINDS
National Institutes of Health, Bethesda, MD USA
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