On Thu, Oct 30, 2025, 12:53 PM Peter Ekstrom via cctalk <
cctalk(a)classiccmp.org> wrote:
  If I single-step, it doesn't seem to happen. But I
have been playing around
 with my test program and I added a loop in the beginning that clears 0-377.
 That loop uses a bne instruction which seems to work fine. When I reach a
 br or jmp instruction, the program fails. I saw in the opcode test for
 macro11
 in the simtools package, the br instruction is tested with 'br   .' so I
 used that in my program and it failed too.
 Now I really need to try this on my hardware 11/23 tonight.....
 
When i toggled in the boot loader in octal, it was always transfer a block
to a fixed location and loop. You were supposed to wai a second or three,
then hit halt, the toggle in that fixed address and jump to it.
Boot roms did this for you and checked the device starus bits to know when
yhe xfer was done. Or just halted and relied on the interrupt to take the
loader out of halt when it then jumped to the bootstrap just loaded. Iirc,
the interrupt trick was way more common.
Warner
-Peter
 On Thu, Oct 30, 2025 at 1:03 PM Martin Bishop via cctalk <
 cctalk(a)classiccmp.org> wrote:
  I would verify that what you intended to load has
been correctly loaded,
 by displaying / dumping 1400 et seq.
 If that is good, I would then instruction step to observe where execution
 leads.
 It may also be necessary to clear the processor's state and maybe issue a
 bus init - however, the simulator startup probably obliges.
 Martin
 PS FWIW all the vectors and traps (0 to 400 in big handfulls) are
 uninitialised (by you), so any of those could take you to exciting
 
 places -
  eg 5271
 -----Original Message-----
 From: Peter Ekstrom via cctalk <cctalk(a)classiccmp.org>
 Sent: 30 October 2025 14:40
 To: General Discussion: On-Topic and Off-Topic Posts <
 cctalk(a)classiccmp.org>
 Cc: Peter Ekstrom <epekstrom(a)gmail.com>
 Subject: [cctalk] Re: Looking for a bootloader
 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.
 Any pointers would be greatly appreciated.
 -Peter
 On Tue, Oct 28, 2025 at 3:38 PM Peter Ekstrom <epekstrom(a)gmail.com>
 
 wrote:
 > Wayne, Warner, Glenn,
 >
 > Thank you very much for your responses!
 >
 > Wayne,
 >
 > I took a look at the PDP11GUI files and it is quite complex. I setup
 > the GUI on a PC here and tried it against my PDP-11/23 but wasn't able
 > to get it to work.
 > Not sure what I did wrong but I am definitely keeping it, and will go
 > through that source a bit later. I'm sure I'll learn a lot from it.
 > Thank you for the tip!
 >
 > Warner,
 >
 > Right now I prefer assembler because I am trying to learn more about
 
 it.
  > But I glanced at the BSD loader in C and
find it quite interesting. I
 > am going to go though that too a bit later. Thank you for this tip as
 > well!
 >
 > Glen,
 >
 > I did look at the sources you mentioned and they were a bit more
 > bite-sized. So I have tinkered with it and am actually able to use it
 > to boot an 11/23 in SIMH using that code. I have also cobbled together
 > a little boot menu and incorporated this loader there. Thank you for
 > those pointers!
 >
 > Thank you all!
 >
 > -Peter
 >
 > On Tue, Oct 28, 2025 at 6:38 AM Glen Slick via cctalk <
 > cctalk(a)classiccmp.org> wrote:
 >
 >> (DU) MSCP UDA50(RAxx) disk:
 >>
 >> 
https://ak6dn.github.io/PDP-11/M9312/
 >>
 >> 
https://ak6dn.github.io/PDP-11/M9312/23-767A9/23-767A9.mac
 >>
 >> 
https://ak6dn.github.io/PDP-11/M9312/23-767A9/23-767A9.lst
 >>
 >>
 >>
 >> On Mon, Oct 27, 2025, 4:48 PM Wayne S via cctalk
 >> <cctalk(a)classiccmp.org>
 >> wrote:
 >>
 >> > Maybe look at pdp11gui ?
 >> > I think it downloads a boot loader so the code may be there.
 >> > <https://retrocmp.com/tools/pdp11gui>
 >> > 
PDP11GUI<https://retrocmp.com/tools/pdp11gui>
 >> > 
retrocmp.com<https://retrocmp.com/tools/pdp11gui>
 >> > [
favicon.ico]<https://retrocmp.com/tools/pdp11gui>
 >> >
 >> >
 >> >
 >> > Sent from my iPhone
 >> >
 >> > On Oct 27, 2025, at 15:58, Peter Ekstrom via cctalk <
 >> cctalk(a)classiccmp.org>
 >> > wrote:
 >> >
 >> > I am looking for the assembler listing for a bootloader for
 >> > booting
 >> from
 >> > MSCP disks like RD-disks.
 >> > Google has not been very helpful and my assembler knowledge is not
 >> enough
 >> > for me to write one from scratch. Does anyone have one they can
 
 share?