PDP-11/45 RSTS/E boot problem

Tony Duell ard.p850ug1 at gmail.com
Mon Feb 11 11:34:11 CST 2019

On Mon, Feb 11, 2019 at 4:13 PM Jon Elson via cctalk
<cctalk at classiccmp.org> wrote:
> On 02/11/2019 07:04 AM, Noel Chiappa via cctalk wrote:
> > A look at the RK11 registers after the swap-out showed an anomaly; something
> > about the extended memory address bits? (Maybe a multi-block transfer than
> > crosses a 64KB boundary? That would explain the address sensitivity we were
> > seeing.) Hopefully he'll track it to its lair shortly.
> >
> >
> OH, BOY!  I think you may have found it.  Likely some disk
> controllers did NOT SUPPORT crossing 64K boundaries!  The
> diags would not detect that, as it was likely expected
> behavior.  I would suspect the driver would need to break up
> these operations.

I _think_ the RK11-C should cross a 64K boundary correctly. There's
an output from the low 16 bits bus address module (M795) on pin BP2
'D15 RKBA=ALL 1 L' (page 27 of the schematic on Bitsavers)  that
goes to the counter that holds the 2 extended bits, pin C1 of the M239
in slot A17 (page 13 of the same .pdf)

[I am working from 'RK11-C_schemFeb1971.pdf' from bitsavers]

Of course if there is a fault in this area then it will not correctly increment
the top 2 bits, but that might give you somewhere to check.


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