strange number corruption on pdp11/34

Jacob Ritorto jacob.ritorto at
Thu Jan 29 20:30:36 CST 2015

ok, now with my 'good' 11/34 board set (not the set with the mysterious
zero bug) installed, I re-ran xxdp against the rl02.  I'm getting proper
prompts with the address and vectors supplied with non-zero numbers as
defaults. I just hit return like I had been doing with the 'zero-bug' cpu
boards and this time, the tests run, the drive blinks wildly like before,
and I get real results with real numbers filled in.  I think this pretty
conclusively proves that there's something really weird (mysterious zero
bug) going on with my other board set.

On Thu, Jan 29, 2015 at 7:15 PM, Johnny Billquist <bqt at> wrote:

> On 2015-01-29 20:14, Pete Turnbull wrote:
>> On 29/01/2015 18:32, Jacob Ritorto wrote:
>>> Johnny, you're insisting that I put in the real numbers for address
>>> and csr
>>> for testing the drive (for instance).  I'm going to do that next, here.
>>> But are you understanding that some of us think that the reason it
>>> prompts
>>> a zero default is that it's a manifestation of the zero bug and that the
>>> real value *is* actually safe but hidden in memory?  Did you see the
>>> RSX-11M crash dump I posted in the other thread?
>> I didn't see a crash dump, but did you see what I posted yesterday?
> I haven't seen any crash dumps either.
>  The default in XXDP for CSRs is very often zero, and I'm pretty sure it
>> is so in the RL02 diagnostics (I've ont checked the listing for that
>> particular one, but I did look at some others that were more readily to
>> hand).  So when it asked you for input and you just hit "return", you
>> really did tell it zero.  Applying the principle of Occam's Razor, and
>> assuming the simplest solution is the correct one, you got a lot of
>> zeros back because it was accessing memory instead of the controller you
>> wanted.
>> It's hard to believe you have a CPU fault that consistently prints
>> numbers as zeros yet happily boots three different OSs.  Still, I'll
>> change the tune if you re-run XXDP with sensible inputs.
> Totally agree with that one.
>         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

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