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Re: SIMH V3.2 released

From: Bob Supnik (
Date: 04/06/04

Date: Tue, 06 Apr 2004 10:42:39 -0400

On Tue, 6 Apr 2004 11:58:56 +0200, Christian Corti
<> wrote:

>In alt.sys.pdp11 Bob Supnik <> wrote:
>> SIMH V3.2 was released today, on the web at
>> 5. LGP30/LGP21 - new simulators of Royal-Mcbee drum/disk based systems
>> from the late 50's/early 60's.
>Nice to see this in simh, I will make some comments on this (we have the
>only working LGP-30 incl. all docs, SW etc.):
>- You should not provide a builtin 10.4 replacement into the
> simulator. Instead you have to provide the means to load 9.0 and
> *eventually* 10.4 from tape. This is because there are programs that
> have to be loaded by 9.0 and uses tracks normally used by 10.4 (tracks
> 0000 to 0263).

If you'd like to suggest a mechanism for 'booting' the tape typewriter
or the paper tape reader, I'm happy to implement it. One possibility
is to set up memory with the 'result state' of the 9.0 procedure and
then transfer control to it. Note that the 'builtin' 10.4 takes no
space on the drum; it is simulator code, not simulated instructions on
the drum.
>- You have to provide loading and saving routines for storing the drum
> and registers contents into a file and retrieving it the next time.
> This is because you can stop a running program, shut down the machine,
> have a nice weekend, and come back next week and restart your program
> where you have stopped it last time.

SAVE <file> does exactly this; RESTORE <file> restores the machine
>- You should provide a visual scope and buttons display because
> operating a LGP-30 makes heavy use of the console. Even some programs
> (some games for example) need the bitwise display of the registers in
> order to be usable or pushing a breakpoint or the transfer button.
>- You should have a way to support the two ribbon colors (red and black)
> of the Flexowriter.
Both of these require graphics support, which is in development.
Portability across Windows, Unix, VMS, and Mac OS/X makes graphics

>- You urgently need a way to show the user whether the machine is
> running or waiting for an input.
The simulator prints out a prompt (`) if it is waiting for manual
input. If this isn't sufficiently clear, it's easy to change the
prompt to something else (like [Waiting for input], or an audible

>- Because of the lack of key accessable button functions (e.g. the
> F-Keys) loading 9.0 is a real pain.

What's an F-key? There's no mention of this in the documentation.
All of the documented functions of both the front panel and the tape
typewriter are implemented via SET commands, eg,

set cpu fill

will transfer the A register to IR; or to directly set IR

set cpu fill =<hex value>

The 9.0 procedure is indeed very painful. Since the purpose is to get
about 5 words into memory, the results can be recreated with deposit
commands, eg,

sim> d addr val
sim> d addr val
sim> d c val
sim> d a val
sim> run
>- I wasn't able to load a program because the interface is not really
> usable and the builtin 10.4 lacks some commands.

Please let me know what additional parts of 10.4 are required. I was
working with a collection of transcribed paper tapes that I found on
the Web, and they load correctly.

I'm also happy to change the interface which is, admittedly, quite
wordy compared to pushing buttons. Standard functions (such as
loading 9.0 or 10.4), once implemented, could be written up as script
files, which are then executed via the DO command. Note, though, that
the purpose of the simulator is to run software, not to recreate the
operational experience of an LGP-30. If functions can be done through
existing simulator interfaces (see comments on 9.0), that suffices.
>- The first mentions of the LGP-30 are dated from 1954 (or even before)
> so it is quite an "old" machine.
>BTW I too have written a LGP-30 simulator. It is written in TurboPascal
>and runs fine under DOS or in dosemu. I needed one after the
>restauration phase of our LGP-30 in order to verify its functions and to
>do cross development. It has many nice features like sending Flexo
>output to a printer, drum save/restore, etc. I always wanted to make it
>public for downloading one day.

I'd encourage you to publish it.

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