Re: PDP-11/45 RSTS/E boot problem

[Paul Koning via cctalk]

> On Feb 11, 2019, at 11:12 AM, Jon Elson via cctalk <cctalk@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.

You may be thinking about PC controllers like the floppy controller.  I can't 
remember ANY DEC DMA device controller that had boundary crossing limits of any 
kind.  It certainly isn't a restriction in the RK11.

        paul