ISO: PDP-11/40 LTC and Stack Limit options

Josh Dersch derschjo at
Mon Nov 21 21:19:38 CST 2016

On 11/21/16 5:47 PM, Noel Chiappa wrote:

>      > From: Josh Dersch
>      > The 11/40 is mostly working ... but I've been unable to boot anything
>      > (like XXDP, for example).
> What are you trying to boot from?
I've tried an emulated TU58 and (most recently) a UNIBUS SCSI controller 
that I'm fortunate enough to have.

>      > Slot 9 of the CPU backplane is supposed to be an SPC slot but it
>      > doesn't seem to work
> Missing/hard-wired BG/NPG jumpers on that slot, maybe?
The NPG jumper on slot 9 is not present, and it has no effect on the NPG 
chain if i jumper it or not (the bus seems happy otherwise...) There 
appears to be no continuity between CA1/CB1 of slot 9 and CA1/CB1 of the 
SPC/MUD slots in the rest of the system.  It's very puzzling.  I need to 
sit down with the wire list (and copious Excedrin) and probe things out.

> If not, plug one of Guy's UA11's into that slot, and see what's up! :-)
>      > I assumed I needed the KJ11-A because the KT11-D manual specifies
>      > (bottom of page 2-1): "When the KT11-D Memory Management Option is
>      > added to an existing PDP-11 system, the KJ11-A Stack Limit Register
>      > Option must also be added." So I assumed the MMU required this option
>      > be present...
> Hmm, I didn't recall that; not sure I ever knew that! (Sorry!)
> I spent a short time looking at the KT11-D and KJ11-A prints, trying to see
> exactly what the KT11-D wanted, but I wasn't able (yet) to fully grok the
> interaction.
> >From the KJ11-A prints, you can probably work around not having a KJ11-A card
> by strapping the relevant outputs high or low (as the case might be), i.e.
> simulating a KJ11-A which is not reporting a problem. Like I said, V6 doesn't
> use the SLR for anything, so it's it's not actually working (i.e. reporting
> stack transgressions), no biggie.
> If you're determined, I did scan in a KJ11's PCB, so it would probably be
> possible to produce 'after-marked' ones - it's not a very complicated card.

Thanks for looking into it.  I'm not desperate for a KJ11 yet, but it's 
good to have resources should one need to be built...

>      >> You will also need the KE11-E (M7238), as the Unix C compiler emits
>      >> MUL, DIV etc, and even the bootstrap uses them. The KE11-F (M7239) is
>      >> useless; the V6 Unix C compiler doesn't generate that type of PDP-11
>      >> floating point.
>      > Yeah, that might be harder to find, I'd forgotten about that
>      > requirement. I suppose I could run Ultrix-11 instead (I have that on my
>      > 11/34 at the moment) as it'll run sans floating point hardware,
> We seem to be having a communication failure. You don't need floating point
> to run V6 or V7 on an 11/40. In addition, the hardware floating point
> hardware on the 11/40 (the FIS) is a variety that Unix doesn't support anyway
> (in the sense of, the C compiler doesn't generate FIS instructions).
> It's the Exteded Instruction Set (EIS) card (which supports MUL, DIV, ASHC,
> etc) which is necessary. No way UNIX (of any flavour) will run without those
> instuctions (and thus, that card). If you don't have an M7238, start
> looking....
Sorry, sorry -- long day and it's been awhile since I looked at the 
11/40 in depth (just dusted it off last night).  I thought I had picked 
up an EIS years ago shortly after I picked up the machine but either my 
memory is faulty or it's disappeared somewhere (the former is more 
likely at this point, I actually do have things somewhat organized 
here).  So that adds another level of fun.

Maybe at this point I should be happy to get RT-11 working :).

> BTW, what is your mass storage device? RL's? If so, vanilla V6 doesn't support
> RL's, but I do have a V6 RL driver, I can either build you a system that will
> run on an RL, or (if you bring up V6 under an emulator, so you can build
> systems, etc) provide it so you can add it. You'll also need an RL bootstrap
> (again, those are available, but not in vanilla V6).
> Also, how are you getting the bits onto the mass storage? V6 can only be
> 'cold installed' onto a blank machine from a TM11 or TM02 tape drive. Failing
> that, you have to put a V6 filesystem onto a disk on some other machine. Do
> you have the ability to write packs on another machine/OS, and the ability to
> get a Unix file system onto that system? Failing that, I'm in the process of
> getting VTServer working to transfer V6 over a serial line to a blank machine
> (my situation) - I got distracted before I got 100% finished, but I have it
> all scoped out, and can get it done in a couple of hours from where I am now.

I have an RK11 and an RK05 (with the option of a 2nd RK05 if I ever get 
some mounting rails for it.)  I know the RK05s are tight storage-wise. I 
also have an RL02 but I need to repair an RL11 first.  (And there's 
always the SCSI controller, should I get up the nerve to backport an 
MSCP driver...) I should be able to wrangle bits onto media either using 
what I have, or by using stuff at the LCM, but the VTServer option 
sounds nice too.  The RL bootstrap and driver would be very useful to 
have, thanks!

Thanks again,

> 	Noel

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