I have been trying to talk to a board using the /dev/mem interface.
However, when I open with O_RDWR, it fails with EPERM.  I have tested 
this as root, set the permissions to 666, etc.  Nothing works.  Note
also that it worked under AMIX and (on another system) under FreeBSD.
Reading the source, I was further confused by the fact that open was
mapped to the stub nullop() which doesn't do anything except succeed!
The implication is that access should be solely determined by the
permission bits.

Is there a trick?

-- 

John Codona
jlc@kepler.whats.att.com