Interesting RK8E fault

[Josh Dersch]

On Sat, Dec 8, 2018 at 10:43 PM Guy Sotomayor Jr <ggs at shiresoft.com> wrote:

>
> On Dec 8, 2018, at 10:36 PM, Josh Dersch <derschjo at gmail.com> wrote:
>
> On Sat, Dec 8, 2018 at 10:33 PM Guy Sotomayor Jr <ggs at shiresoft.com>
> wrote:
>
>>
>> > On Dec 8, 2018, at 8:50 PM, Josh Dersch via cctalk <
>> cctalk at classiccmp.org> wrote:
>> >
>> > On Sat, Dec 8, 2018 at 7:24 PM Paul Anderson via cctalk <
>> > cctalk at classiccmp.org> wrote:
>> >
>> >> Are you using the same pack for the 8 and the 11
>> >>
>> >
>> > I connected the drive I normally use with my 11/40 to the 8/e for
>> testing
>> > to help narrow down where the fault was.
>> > I used a 16-sector pack in all cases.
>>
>> You should be using 12 sector packs on the 11 and 16 sector packs on the
>> 8.
>>
>> I’m actually surprised the 16 sector pack worked on the 11.
>>
>
> In all cases /pertinent to this discussion/, i.e. with the RK8E attached
> to both the 11/40's RK05 and the RK05 I've restored for the 8/e.
>
> I have 12-sector packs that I normally use with the 11/40.
>
>
> OK, just so that I understand the problem:
>
>
>    - Do you see the problem only on the RK05 you restored for the 8/e and
>    don’t see it on the drives from the 11/40?
>    - Or do you see the problem on all the drives when hooked to the 8/e
>    and when using a 12 sector pack on the 11/40 you don’t see the problem when
>    using any of the drives on the 11/40?
>    - Or do you see the problem on the drive restored for the 8/e but not
>    on the drives from the 11/40?
>
>
>
Just to clear this all up :) :

I have an RK8E that's exhibiting some odd behavior.  Amongst other things
I've poked at, in order to help pinpoint the problem to the RK8E I ran the
formatter and exerciser using the RK8E with both the RK05 I restored for
use with the PDP-8/e *and* an RK05 I'd previously restored and which works
100% perfectly with my PDP-11/40.  In both cases (i.e. with the 8/e's RK05
and the 11/40's RK05) I used 16-sector packs (because I wouldn't expect it
to work on the PDP-8/e otherwise).

The diagnostic and formatter behave identically with both drives.
Therefore:  I assume the problem is with the RK8E.

If anyone has any insights into the inner workings of the RK8E (in
particular the CRC circuit, since it's used to compare the on-disk cylinder
address stored in the header with the cylinder selected by the RK8E's
address register) please let me know.

Thanks again,
Josh




> TTFN - Guy
>
>
>>
>> >
>> >
>> >>
>> >> On Sat, Dec 8, 2018 at 8:54 AM Bill Degnan via cctalk <
>> >> cctalk at classiccmp.org>
>> >> wrote:
>> >>
>> >>> On Sat, Dec 8, 2018, 1:02 AM Josh Dersch via cctalk <
>> >> cctalk at classiccmp.org
>> >>> wrote:
>> >>>
>> >>>> On Fri, Dec 7, 2018 at 9:58 PM Josh Dersch <derschjo at gmail.com>
>> wrote:
>> >>>>
>> >>>>> Hi all --
>> >>>>>
>> >>>>> Finally got all the parts together (and my act together) to actually
>> >>> get
>> >>>>> an RK05 lashed up to my PDP-8/e -- only took a decade or so :).  I
>> >>> fixed
>> >>>> a
>> >>>>> few problems with the RK05 and it appears to be behaving very
>> nicely.
>> >>>>>
>> >>>>> The RK8E controller is mostly working properly but fails
>> >> interestingly
>> >>>>> when running the formatter, and during the exerciser -- on cylinder
>> >> 128
>> >>>> and
>> >>>>> 192 and very infrequently on cylinder 64 it will get a cylinder
>> >>> mismatch
>> >>>>> when doing the seek.  When running the formatter during the
>> >>> verification
>> >>>>> pass, on cyls 64 and 128 if I retry the read it'll continue without
>> >>>> issues,
>> >>>>> but it's never successful on a retry on cylinder 192.  I tried
>> >> hooking
>> >>> it
>> >>>>> to the RK05 in my 11/40 and it exhibits the same behavior, so I'm
>> >>>> guessing
>> >>>>> the drive isn't at fault.  And the error is consistent across packs
>> >> (of
>> >>>>> which I have only two).
>> >>>>>
>> >>>>> Apart from that fault the drive and controller seem to work fine --
>> I
>> >>>>> wrote out an OS/8 pack with Adventure on it (or at least the first
>> >> 191
>> >>>>> cylinders of it) and it works without issue.
>> >>>>>
>> >>>>> Reading the RK8E service docs and schematics, the cylinder address
>> >>>> compare
>> >>>>> is done by reusing the CRC buffer, so I suspect the issue is in or
>> >>> around
>> >>>>> there -- the big problem is that debugging it is rather painful
>> since
>> >>>> that
>> >>>>> logic is in the middle board of a three board set, with jumper
>> blocks
>> >>> on
>> >>>>> top -- so bringing it out on an extender isn't an option.  I'm
>> >> curious
>> >>> if
>> >>>>> anyone's seen this issue or is so very familiar with the logic that
>> >> the
>> >>>>> fault is obvious.
>> >>>>>
>> >>>>> I suspected the 7496 shift register at E14 which takes in the
>> >> cylinder
>> >>>>> address to be compared w/the header on disk, and I went ahead and
>> >>>> replaced
>> >>>>> it in the hopes that I'd get lucky, but no go.
>> >>>>>
>> >>>>> Anyone have any advice?
>> >>>>>
>> >>>>> Thanks,
>> >>>>> Josh
>> >>>>>
>> >>>>>
>> >>>> I'll add that during the format/verification the drive seeks properly
>> >>> (i.e.
>> >>>> it's not missing a step or overstepping), which I've confirmed by
>> >>> watching
>> >>>> the thing walk through the tracks with the cover off.
>> >>>>
>> >>>> - Josh
>> >>>>
>> >>>
>> >>> Partitions as rka0 / rka1?
>> >>> B
>> >>>
>> >>>>
>> >>>
>> >>
>>
>>
>