Saturday, October 2, 2021

RetroChallenge 2021-10 intentions (RC2014 Projects Braindump)

Hi all.  So I've decided to settle on working on various RC2014-based projects for this RetroChallenge.  I have a few related projects that I'm kind of in the middle of and have set aside for various reasons... the primary of which being my "ooh... shiny!" reason, where I get pulled off existing projects to start something else thanks to my brain.  ;)

Most of my RC2014 projects are all intertwined so it makes sense to kinda work on all or each of them simultaneously...

Anyway, here's a few things I'd like to work on this month:

"Lego Brick" RC2014

This is my main RC2014 system.  The display on it somehow developed a weird glitch on it that looks like Lichtenberg lightning print.  
I have a spare LCD panel that I can swap into place, i just haven't done it yet.  

Llama Vampire-Storage system (LLVS)

This is my "storage over serial" system that I started working on in the past.  It basically uses something like ANSI escape sequences over your serial console to do disk accesses. It could eventually be used for other devices as well like network and printer access, reatime clock, GPIO, etc.

Eventually, it would be great to have the LLVS "type in" a BASIC program that is a simple bootloader that will load in a custom CP/M kernel with  LLVS routines, so that a super cheap (and slow) CP/M system can be booted without boot roms, CF card module, or any of that expensive stuff.  

Also to be included with this are tools that natively talk the LLVS protocol so that you can retrieve and store content to your host machine from "standard" CP/M systems.

Obviously this also requires a host/terminal side of things too, which is being implemented in python currently, but could easily be reimplemented in C/C++ to be compiled in with the Pi Zero Serial Terminal module, so that you can use the Pi Zero's SD card as your CP/M storage device.

RC2014 Pro Build

I have most of an RC2014 Pro kit around, and I'd like to build up the various parts of it including the backplane, compact flash storage, and so on, so that I can finally do a native CP/M boot up.  This could be combined with the LLVS above to allow for easy transfers to and from the CP/M system and your "host" system.

I have a few modules that I want to build up and test and experiment with... i've just never really dug in to work on it.


Llichen-80 is a CP/M kernel-based system that takes my LLVS-based system a step further, and adds in the TMS-9918A video card as its main graphics display.  This could be used simultaneously with the standard terminal, or as a replacement to it.  I haven't quite figured all of that out yet.  

I plan on making a few CP/M programs that configure the TMS and download files from the mass storage device into it, for loading fonts, graphics, etc.  Or just to use it for console output.

For use with a single composite display, I also have an hardware video switcher (simply two relays with a digital gpio input) that could be connected to a digital out from the RC2014 or as a GPIO line from the Pi Zero on the Pi Zero Serial Terminal card.

I have some of the basics of this working, but nothing really solidified.

The Llichen-80 system consists of an RC2014 CPU, Clock, Pi Zero Serial Terminal cards, along with the TMS9918A video card.  The Pi Zero Serial card is set up with a PiZero W, and is not running the standard PiGfx kernel, but instead running linux, so that it can run my python terminal application, so that i can add in all of the LLVS code

RC2014 Mini / Micro Mods for CP/M

It's well known that by removing some components on these boards, you can use them as a standard CPU module when upgrading to a CP/M system... replacing the fixed RAM/ROM for the switchable RAM/ROM and so on.  But it would be nice to be able to simplify this so that the RAM/ROM on the RC2014 Mini or RC2014 Micro could be made to be switchable using a simple jumper to connect to the logic needed to do the switching.  Not sure that this even makes sense being that the Mini CP/M upgrade exists, but I'll be thinking about it...

RC2014 Peripheral and IO Switcher Traffic Cop Thing

This one is more of a musing about a new Z80 system architecture, but it could be prototyped using lightly modified  RC2014 modules.

I feel like a peripheral manager type of card might be useful for a new system... one board that has ALL of the logic for peripherals, to switch them on and off, so that peripheral cards needn't have this logic repeated on all of them.  Then it could be vastly simplified for chip count.  It could handle catching bus requests for reading/writing memory or port based io, and work it out to be a single enable/disable line to be run to your peripherals.  That way peripheral cards could be made much simpler, and more easily moved around in the RC2014 memory and IO space... perhaps even live while the system is running.  It would be easy to make it such that any peripheral could be moved to any address, enabled, disabled, etc. Hmm...


  1. Great looking projects! Just a thought re: LLVS - Zmodem has a little-known ZTSPARS command for transferring blocks of sparse file disk images. I found it very useful to transfer disk images using gnu screen's built in zmodem command sensing to a 6809 based SBC. Since Zmodem is widely implemented and has built-in error detection, it could save you some trouble.

    1. Great suggestion! I had thought about Zmodem in the past, and I figure that I could add ZModem eventually, but my first goal with it is that I need it to be super tiny to make the bootloader be as small as possible, and also the disk routines have a space limitation for the CP/M BIOS. IIRC a lot of ZModem has to do with error correction which was super necessary when communicating over serial lines and modems to distant machines, whereas here, the host and the target are literally an inch apart.

      I certainly could add ZModem in the future, and then some CP/M tools to use it directly, but for now, it's gonna be my super lightweight simple protocol... at least until my feet are moving. ;)

      Thanks for the suggestion!!!