Access to IOPAGE Registers using PDP-11 Opearting Systems

dundas at dundas at
Thu Nov 22 11:10:45 CST 2007

> ons 2007-11-21 klockan 12:00 -0600 skrev "John A. Dundas III"
> <dundas at>:
>> Jerome,
>> I can speak for RSTS with some authority, RSX with somewhat less
>> authority.
>> At 9:17 PM -0500 11/20/07, Jerome H. Fine wrote:
>> >I doubt that RSX-11 or RSTS/E allow a user access to the IOPAGE
>> >even via PREVIOUS  DATA space.  Can anyone confirm this assumption?
>> Address space in the I/O page for RSTS jobs (processes) was not
>> directly available.  The APRs are always controlled by the OS.  It
>> MIGHT be possible for a privileged job to use PEEK/POKE SYS calls to
>> access the I/O page in the way you suggest but it would be
>> particularly difficult.
> I thought RSTS/E had some way of remapping the address space as well.
> Can't you remap parts of your memory to some shared region, for example?

Yes, shared regions (libraries and others) are supported.  However as a
general purpose timesharing system, RSTS insisted on direct access of the
I/O page only by the kernel.

So while it _might_ be possible to peek/poke a device CSR from user space
(I never had occasion to try but could imagine a few possible approaches),
it would not be possible to set up, e.g., an interrupt vector in user


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