advice / suggestion wanted PDP 11/40 only boots XXDP, not RT11

[Jerry Weiss]

My recollection is that XXDP tries not to use Interrupts or DMA, unless 
it has to.

I would check out those areas first for problems if it hangs in RT-11.

Jerry


On 1/31/19 2:26 PM, Bill Degnan via cctech wrote:
> My PDP 11/40 suddenly lost it's ability to boot RL02 disks except the XXDP
> disk.  I have two drives, both boot up an XXDP (I have more than one) just
> fine, but any formerly-working RT-11 (v 5, 5.1, 5.3) no longer boots, it
> just hangs.  I have been troubleshooting, running the 11/40 XXDP tests, but
> they seem to just hang too. And I am not a big fan of XXDP anyway.  I have
> cleaned the drive heads, the disks are ok.  I can load BASIC just fine from
> PDPGUI "tape" through the serial card (M7800)
>
> Any off the cuff suggestions why this specific issue would arise?   Power
> seems ok, looking for dumb reasons that I missed.  I have swapped out CPU
> cards, does not make any difference.  I am pretty sure it's a UNIBUS
> interference issue, at least that's my working theory.  I suppose there may
> be an RT-11 boot instruction call or routine of the CPU that XXDP does not
> exercise explaining why XXDP boots.    Maybe RAM locations.
>
> In the end I just have to work through everything, but I am open to
> suggestions to help cut down the time spent diagnosing the problem.
>
> Thanks in advance, I will be around tonight (East Coast USA Time)
>
> Bill