I purposely kept it simple. The thing is, if I change the CPU to an 11/23+ it keeps running. I did notice most other CPU models also aborts. A loop waiting for keyboard input could stay waiting for quite some time. Although I could see an interrupt happening. I disabled all the devices I wasn't using in SIMH, hoping to prevent stray interrupts but it still did the same thing.
And just for clarity, this little program is the only thing I am loading. I start the simulator, set the cpu, load the binary and jump to its start address. There is no operating system or anything else running. Just the bare simulated metal. - Peter On Thu, Oct 30, 2025 at 8:03 PM Jon Elson via cctalk <[email protected]> wrote: > On 10/30/25 09:39, Peter Ekstrom via cctalk wrote: > > Anyone here familiar with programming the 11/23 (KDF11-A) in assembler, > > bare metal? > > I have been trying to get a very simple test program to run on it but it > > keeps halting on > > an address outside of the program. Seems to always be the same address > > which is why > > I am thinking I must be missing something. The program runs fine on an > > 11/23+ or 11/70. > > > > Below is the listing: > > > > 1 000000 .asect > > 2 014000 .=14000 > > 3 014000 012706 002000 start: mov #2000,sp > > 4 014004 000240 loop: nop > > 5 014006 000776 br loop > > 6 .end > > > > I have a hardware 11/23 but for convenience I have been testing on a SIMH > > 11/23 by > > loading the binary from the simh prompt and then jumping to the start > > address. > > I have tested the same code on 11/23+ and 11/70 CPUs and it runs fine. > > > > I am working in Linux and am using the following Macro11 cross-assembler: > > > > macro11 - portable MACRO11 assembler for DEC PDP-11 > > Version 0.8 (07 Jul 2022) > > Copyright 2001 Richard Krehbiel, > > modified 2009 by Joerg Hoppe, > > modified 2015-2017,2020-2021 by Olaf 'Rhialto' Seibert. > > > > I then use the obj2bin.pl utility by Don North to convert from object > > format to binary load format. > > > > The following is what happens: > > > > PDP-11 simulator Open SIMH V4.1-0 Current git commit id: 29d39002 > > sim> set cpu 11/23 > > sim> load test.bin > > sim> g 14000 > > > > HALT instruction, PC: 005271 (HALT) > > sim> > > > > Am I missing some initialization parts or something? I have looked > through > > various manuals and > > the processor handbook for the LSI-11 but if it is in there, I am missing > > it. > > > WOW, that code is insanely simple. Is it possible there is > a timer (or other) interrupt happening? I can't see any > reason the CPU will jump out of that do-nothing loop. > > Jon > >
