Accessing 8541 registers from user space

[Charles Krinke]

I have a need to be able to read and write the gpio data registers PDATC
and PDATD from a user space program. 

We have a userspace program that succesfully mmaps an offset in /dev/mem
and reads/writes registers in a CPLD at 0xFF00_0000.

The issue seems to be that when I mmap /dev/mem to 0xE000_0D50 to read
the PDATC register, Linux-2.6.17.11 just locks up.

Can anyone shed a little light on why this could be happening?

Charles Krinke