[Simh] Strange PDP-11 behavior

[Johnny Billquist]

Well, Bob definitely nailed why it was halting when set to PDP-11/23 
mode. The LTC is the problem, obviously.

However, I think simh is wrong in doing it this way. The KDF11-AA manual 
clearly documents that the CPU do handle the BEVENT signal, and traps to 
100, unless you remove W4, so why simh pretends that an 11/23 do not 
have an LTC is beyond me.
(See 
http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/dec/pdp11/1123/EK-KDF11-UG-PR2_Mar79.pdf, 
page 2-2)

So, that has been cleared up. I'd say that simh is wrong in not having 
an LTC for the 11/23, and once that is changed, XXDP will run fine on 
the 11/23 both in real life and in simh.

Next, the question of supported versions - I do not have a list, and 
tend to try and run the latest version. However, in this case I think we 
can clearly say that the version of XXDP was not the issue. And in fact, 
V2.2 did run fine on the real hardware (not sure if you mentioned that 
on the list).

The problems you've seen with some other CPUs and controllers are a 
separate issue. Not sure if we can easily figure that one out. Do you, 
by any chance, have a real DEC MSCP controller and some disks, that you 
could test with as well? It might be that there are some issues with 
some CPUs related to MSCP that cause XXDP to fail, as well as bugs in 
XXDP itself.

	Johnny

On 2015-12-30 11:42, Mattis Lind wrote:
>
>
> 2015-12-30 0:12 GMT+01:00 Bob Supnik <bob at supnik.org
> <mailto: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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>
>
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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol