[Simh] Strange PDP-11 behavior

[Mattis Lind]

2015-12-30 0:12 GMT+01:00 Bob Supnik <bob at supnik.org>:

> Regarding Mark Lind's post:
>

Mattis Lind, not Mark Lind.


>
> It's a simple detective problem. Where does an 11/23 differ from an 11/23+?
>
> If you look in pdp11_defs.h, F-11 based systems are grouped together, and
> CPUT_F is used in most feature definitions.
>
> #define CPUT_F          (CPUT_23|CPUT_23P|CPUT_24)      /* all F11's */
>
> There is only ONE place where an 11/23+ is called out as something other
> than a generic F-11 CPU:
>
> #define HAS_LTCR        (CPUT_04|CPUT_05|CPUT_20|CPUT_23P|CPUT_24| \
>                          CPUT_34|CPUT_40|CPUT_44|CPUT_45|CPUT_60| \
>                          CPUT_70|CPUT_J)
>
> That is, the 11/23+ and 11/24 have a line time clock register. The 11/23
> DOES NOT.
>
> When the TST @#172540 occurs, the PSW is set to 350 (IPL 6), locking out
> any clock interrupts. The interrupt vector for NXM, however, sets the PSW
> to 0. That means any pending line-time clock interrupt will occur
> immediately.
>
> On an 11/23+, the line time clock register initializes to interrupts
> disabled. On the 11/23, though, there IS NO line time clock register, and a
> clock interrupt is pending. As soon as the NXM trap completes, an interrupt
> occurs through vector 100, which is set up as follows:
>
> 100/    102
> 102/    0
>
> So the PC is set to 102, which is a HALT instruction, and the simulator
> halts, with the PC pointing at the next instruction.
>
> Everything is behaving as it should. This version of XXDP was not designed
> to run on an 11/23, and it runs on an 11/23+ by coincidence.
>

This is interesting. I have yet to find a comprehensive document that tells
what version of XXDP that run on what model.
This document http://www.dmv.net/dec/pdf/xxdpum.pdf on page  2-2 (26) says
11/23 family is supported. This document seems to relate to V2.4

Now testing SimH with a (compressed) XXDP 2.5 and XXDP 2.2 image give
exactly the same result. Halt.
http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/xxdp/

I really think that it should be possible to run XXDP V2.2 and V2.2 on a
KDF11-A CPU.
Testing on real hardware shows that both KDF11-A and KDF11-B boots up fine.
If I enable LTC on a KDF11-A (have not tested on KDF11-B yet) it will halt
at the very same location.

So it has to do with LTC rather than model in my opinion. So how can I
disable LTC in SimH so that it acts like the LTC switch on the front panel?
"set clk disabled" give "Command not allowed"


>
> Moral: don't run software on hardware models that it doesn't support. And
> compress your disk images before posting them.
>

Please point me to some document that clearly states that XXDP 2.2 (and
2.5) is not possible to run on 11/23 and 11/23+. Second. Sorry about the
uncompressed image.

BTW: I have also tested this very same image on a real 11/04 and it does
boot to XXDP prompt (it does have DL11-W so LTC registers are there) . But
then it is unable to read the disk. Maybe the DU driver is not happy with
the CMD SCSI card. Booting RT11 on the same setup works fine.

Testing on a real 11/03 boots but hangs in a loop somewhere around 150100
and never prints a prompt. (LTC disabled)

But for the two latter it is highly unsure if they are at all supported by
XXDP v2.2

/Mattis


> /Bob Supnik
>
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