[Simh] New simulator for RCA 1802

[Paul Koning]

> On Jun 13, 2020, at 2:01 AM, Stephen Buck <stephenbuck at mac.com> wrote:
> 
> Hi, I’m interested in having a go at writing a simulator for the RCA CDP1802 processor. There is quite a bit of renewed interest in this unique processor and the systems that made use of it, like the Cosmac Elf and a variety of different spacecraft. It had some very unique features, such as the ability to use any register as the program counter. The 1802 had a few successors that added features and a family of peripheral processors. It was used as the basis of commercial products as well as home-brew systems. 
> 
> I’m looking for a good place to start. If you were starting a new simulator for a simple but unique chip which other simulator would you use as a SIMH learning tool? Which simulator structure would best match the variety of systems is was used in?

SIMH is a framework for writing system simulators.  Its particular strength is that it helps write not just the CPU but also the I/O device emulations, and lets you connect them in flexible ways.

If all you want is to simulate a microprocessor, SIMH is probably more than you need (though it should certainly work).  But if you want to recreate some 1802 based systems, especially if more than one, it's probably a good choice.  The documentation is decent and there are a number of existing machine emulations you can use as references.  If there's anything in SIMH you're already familiar with, that's a good starting point.  For example, in my case I looked a lot at the PDP11 emulation.

	paul