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

[Paul Koning]

RT11-SJ is less dependent on interrupts, I think, so that might be another thing to try.

	paul

> On Jan 31, 2019, at 3:55 PM, Jerry Weiss via cctech <cctech at classiccmp.org> wrote:
> 
> 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
>