I'm creating some short test applications which access physical memory on a PCI card, in QNX 4.25O, with watcom debugger
 10.6.

I'm using the qnx_segment_overlay_flags() call along with the MK_FP() macro to create a pointer to the physical memory..
.. then when I use "wd" to step through the application, when I get to the line which accesses the memory with the 
pointer, the system crashes. If I run the application without the debugger, it works fine.

I tried a similar experiment using shn_open() and mmap() calls. The system crashes as soon as I attempt to step over the
 mmap() call, but the application runs fine when I run it on its own.

Is there some compile/link switches I need, or some options for "wd' that I should be using? Or some other words of 
wisdom?