A Question on Physical Memory Access from Applications

Andrew Johnson anj at aps.anl.gov
Thu Aug 9 00:32:20 EST 2001

"Karaaslan, Utku" wrote:
> I have a problem: we've got a number of ADA applications which are
> using direct memory access to certain hardware registers. Under
> VxWorks, this is not a problem as it lacks kernelspace/userspace
> separation. Under Linux, I know I can do direct memory access (through
> /dev/mem), but in this case I want to use the applications as they are,
> with no change to the ADA code. Is there any way to do physical memory
> access transparently wrt the application? Many thanks in advance.

If you don't mind inserting some code into the application startup then
you could probably do something with mmap(), either with /dev/mem or
(safer) by writing your own kernel driver for the relevent hardware that
supports mmap()ing just the relevent physical range into user-space (and
makes it non-cacheable).  It might be possible to use LD_PRELOAD to do
this at startup without changing the application at all, although I
suspect you might have to make some changes to get the address of the
mmapped region - I'm not sure that you could guarantee to place it where
you want in virtual memory.


- Andrew
The world is such a cheerful place when viewed from upside-down
It makes a rise of every fall, a smile of every frown

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