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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
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 specified segreg is already used for other than a previous call to phys.
This system call is obviously very machine dependent and very dangerous. This system call
is not considered a permanent part of the system.
(phys = 52.)
sys phys; segreg; size; physadr
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