strange number corruption on pdp11/34

Jacob Ritorto jacob.ritorto at
Thu Jan 29 12:32:35 CST 2015

Noel wrote:  I'd really recommend fixing at least one more board set -
otherwise, when the
next failure happens, you'll have _no_ working board sets...

  Yep, you're right.  *sigh* more work.  But that's honestly a good chunk
of the fun of this hobby, right?  I guess I should take advantage of the
momentum and curiosity about this bug that we have going here.  I just need
quite a lot of hand holding because I'm still way too green with this stuff.

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?

And to your other query, yes, I'm booting from the rl02 I'm testing with.
I just switch out to a scratch pack once the diag is loaded and ready to
run (hence the warnings about writing on LoaD device).

On Thu, Jan 29, 2015 at 8:48 AM, Johnny Billquist <bqt at> wrote:

> Short question: What did you boot from? The same RL controller and disk
> you then wanted to run diagnostics on? Or did you have a second storage,
> from which you booted?
>         Johnny
> On 2015-01-29 04:29, Jacob Ritorto wrote:
>>  From what I observed, this zeroed-out prompt was just another
>> manifestation
>> of the zeroes bug.  The values were there in memory and were supposed to
>> be
>> offered to the user but got blanked out with zeroes instead.  I had
>> suspected this and just hit enter at the prompt and XXDP did, in fact,
>> exercise the disk.  There were blinking lights and head noise, obvious
>> work
>> being done that wouldn't have, had there actually been real zeroes in the
>> address and csr fields.  I might swap the bad cpu board back in and try
>> again, but now that the problem has been isolated and removed, I'm
>> inclined
>> to just enjoy the pdp11 :)
>> On Wed, Jan 28, 2015 at 10:19 PM, Rick Murphy <rick at>
>> wrote:
>>  At 07:34 PM 1/27/2015, Jacob Ritorto wrote:
>>>  Johnny, I just took the defaults,
>>>  BUS ADDRESS (O)  0 ?
>>> What Johnny said. The prompt says "(O)", not "(0)" - the letter O for
>>> Octal. The zero after that isn't a default, it simply means that the
>>> value
>>> hasn't been set.
>>> There is no default. Or at least no sane one. Zero in this case means
>>> that
>>> it's writing to memory address zero for CSR. The diagnostic should reject
>>> that, but diagnostics are notoriously user unfriendly.
>>>          -Rick

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