[Simh] Strange PDP-11 behavior
Johnny Billquist
bqt at softjar.se
Wed Dec 30 08:14:43 EST 2015
Ah... And I need to correct myself.
Bob didn't say that the 11/23 didn't have an LTC. He said it didn't have
a LTCR... So, in short, you cannot disable the LTC interrupt on the
11/23. Interesting. Weird. Oh well. I can't find any reference to an
LTCR in the documentation, so it would appear that this really is the case.
So, in order to run XXDP on an 11/23, you need to disable the LTC signal
then.
So I correct myself - seems as if simh is doing it right.
Johnny
On 2015-12-30 13:50, Johnny Billquist wrote:
> 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
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