strange number corruption on pdp11/34

Johnny Billquist bqt at
Tue Jan 27 19:02:08 CST 2015

On 2015-01-28 01:34, Jacob Ritorto wrote:
> Johnny, I just took the defaults, thinking that maybe the real value there
> (that was printing as zeroes) was intact.  In fact, the disk did run tests,
> blinking the ready light ferociously.  Then reported all zeroes back :\

That is weird. All the tests I can ever remember running under XXDP 
actually presented the actual correct default values, or else I had to 
put values in there. I have not ever seen 0 presented, and then not 
actually used. But I cannot recall if I explicitly played with the RL 
tests. But I know I've run the MSCP tests, which use the same diagnostic 
supervisor code.

> In a stroke of sheer weirdness, it also managed to boot 2.9BSD from an
> rl02! It actually ran kind of normally.  Even got to multiuser mode and ran
> and compiled a hello world test program I typed in myself using vi!  Crazy,
> eh?


> Per your recommendations, I'm going to try the small test programs with
> math here, shortly; thank you.

Please do. I would at least feel much better if you actually put in the 
correct CSR and vectors...

Also, it would be very interesting to see the error logs from RSX if 
things fail. Assuming you are booting from some other device, otherwise 
the error logs might be hard to write when there is a failure. :-)

And the RSX errors logs are pretty good at telling you what kind of 
problems you might have.

> Also, I grabbed a set of pdp11/34a boards from a dead (ps issues) machine.
> Can I plug them straight into this blackplane that's currently housing my
> misbehaving 11/34?  Backplane markings are very faded but seem to say
> dd11-pk.

I believe the backplane is the same, but maybe someone else could verify 


> thx
> jake
> On Tue, Jan 27, 2015 at 6:13 PM, Johnny Billquist <bqt at> wrote:
>> On 2015-01-28 00:05, Noel Chiappa wrote:
>>>       > From: Johnny Billquist
>>>       > If it comes as far as booting RSX as well as XXDP, there can't be
>>>       > anything seriously wrong with the CPU...
>>> Yeah, I see your point, but why all the zeros, then? That's what I could't
>>> work out.
>>> Anyway, it should be really easy to make sure e.g. ASH, MUL and DIV are
>>> working; it's vaguely plausible that one of them is broken. (Unix V6, I
>>> think,
>>> might even boot even if MUL was broken. I know the bootstrap uses DIV, to
>>> calculate the cylinder in the disk driver.) If not, cross that off the
>>> list,
>>> and try the next thing... Which is?
>> Is noone paying attention to the fact (and my previous comment) about
>> using 0 for CSR and vector???
>>          Johnny
>> --
>> Johnny Billquist                  || "I'm on a bus
>>                                    ||  on a psychedelic trip
>> email: bqt at             ||  Reading murder books
>> pdp is alive!                     ||  tryin' to stay hip" - B. Idol

Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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