PHYS(2) System Calls Manual PHYS(2)
phys - allow a process to access physical addresses
phys(segreg, size, physadr)
The argument segreg specifies a process virtual (data-space) address
range of 8K bytes starting at virtual address segregx8K bytes. This
address range is mapped into physical address physadrx64 bytes. Only
the first sizex64 bytes of this mapping is addressable. If size is
zero, any previous mapping of this virtual address range is nullified.
For example, the call
phys(6, 1, 0177775);
will map virtual addresses 0160000-0160077 into physical addresses
017777500-017777577. In particular, virtual address 0160060 is the
PDP-11 console located at physical address 017777560.
This call may only be executed by the super-user.
PDP-11 segmentation hardware
The function value zero is returned if the physical mapping is in
effect. The value -1 is returned if not super-user, if segreg is not
in the range 0-7, if size is not in the range 0-127, or if the speci-
fied segreg is already used for other than a previous call to phys.
This system call is obviously very machine dependent and very danger-
ous. This system call is not considered a permanent part of the sys-
(phys = 52.)
sys phys; segreg; size; physadr