afborchert / lilith-emulator

Historic Lilith emulator developed in summer 1983 for bootstrapping Modula-2 to another platform

Historic Lilith emulator

This is a Lilith emulator which I developed and used in 1983 to bootstrap a Modula-2 compiler from the Lilith architecture to the Perkin Elmer 3220 architecture.

At that time I had a PDP 11/40 available, and a Perkin Elmer 3220 machine, sources for the Modula-2 compiler for the Lilith, and the binaries (including sources) for the PDP-11 machine. The goal was to develop a Modula-2 compiler for the Perkin-Elmer 3220 architecture.

I couldn't crossdevelop that compiler on the PDP 11 as this machine was available for some limited time only (it was put out of service just months afterwards I have used it) and because of its painful memory restrictions. The latter would have enforced me to use a 5-pass architecture like that of the compiler for the PDP-11 as opposed to the simpler 4-pass architecture for the Lilith. This required me to write an emulator. I had the choice between an emulator for the PDP-11 or the Lilith and chose the latter as documentation was available and the Lilith architecture seemed to be significantly simpler.

As I had no binaries of the Lilith compiler in Lilith code, I had to cross compile it on the PDP-11 using the Modula-2 compiler for the PDP-11:

     +------------------------+          +------------------------+
     | Modula-2        Lilith |          | Modula-2        Lilith |
     +------+          +------+----------+------+          +------+
	    | Modula-2 | Modula-2        PDP-11 |  PDP-11  |
	    +----------+------+          +------+----------+
			      |  PDP-11  |
			      +----------+

In the next step it was possible to generate the Lilith code. (There was some challenge, though, as this compiler was somewhat too big for the PDP-11 architecture. This step worked out once I stripped everything out of the sources which was not required to let the compiler compile itself.)

     +------------------------+          +------------------------+
     | Modula-2        Lilith |          | Modula-2        Lilith |
     +------+          +------+----------+------+          +------+
	    | Modula-2 | Modula-2        Lilith |  Lilith  |
	    +----------+------+          +------+----------+
			      |  PDP-11  |
			      +----------+

The resulting code was moved to the Perkin-Elmer 3220 architecture and run by emulator which is to be found in the src directory.

At that time we run UNIX Edition VII from Wollongong on the Perkin-Elmer 3220 architecture. We had just a C compiler which was derived from the original C compiler developed by Kernighan and Ritchie. In consequence, you'll find in the src directory ancient K&R style. At that time I didn't care much about portability issues and was just happy that it worked out to bootstrap the Modula-2 compiler. I never intended to polish up this code or use it for another purpose. It was intended as a temporary project only which took me one week to develop.

It is now quite impossible to get this running again under a recent C compiler or a recent system. No ANSI C compiler will accept this code and even if everything gets tweaked such that it is accepted, it still won't run because there exist far too many portability issues. The emulator depends on an evaluation order generated by the K&R compiler at multiple occassions which, however, was never guaranteed by C. The only method to get this code running is to compile and run it under an emulator for this ancient architecture using an installation of UNIX Edition VII which is fortunately now freely available.

Links:

• http://simh.trailing-edge.com/ (The Computer History Simulation Project)
• http://simh.trailing-edge.com/kits/iu7swre.zip (Unix Edition VII)

I make this code available under the terms of the GNU General Public License (see the attached file LICENSE) for the purpose of documenting a historic development process.

See https://github.com/afborchert/lilith for more infos.

Andreas F. Borchert