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A project log for rhombus

An open-source minimalist 68020 based single board computer

Jason WesterveltJason Westervelt 07/11/2017 at 20:520 Comments

My sincere apology for the extended delay. Job and life kinda smacked me upside the head at the same time. :/

I decided that the original intent of this project was to make something minimalist, open-source and easily replicated by the masses. To that extent, the current state of rhombus meets those goals, however I need to do some polish on the code as well as the hardware, and do a good deal of documentation explaining how to get ROMs flashed, how to program the CPLD, etc. Ideally I'd love it if someone with minimal experience could stumble across this project when searching for something to do with an old 68020 that they found inside a laser printer or other salvage... and make something that actually works and can serve as a learning aid.

But whilst working on this project, which has been a learning experience for me, I've thought about many things that I'd love to do with the system that I have built. Things like booting linux, which require an MMU, as well as interfacing with a bus such as VME, will take this project out of the realm of minimalism.

The two systems will remain closely related, enough so that starting a new hackaday project would seem unwarranted. One thing that hackaday.io seems to lack is a way of versioning a project. This kinda drives my inner OCD demons nuts. What I plan on doing is splitting the project into rhombus v1 and rhombus v2, with v2 being focused on modularization and adaptation to the VME bus, as well as development of peripherals (SID based stereo sound, SCSI adapter, network adapter, etc). This should let my audience have the best of both worlds... a simple system one can build to experiment with homebrew computing, and a more complex system which can be put to use doing real-world tasks.

All that being said, I have a board which I need to send to Oshpark. It's a full size VME board and has dimensions of about 13.5x9.5 inches. That is a $600 investment to run off a board of this size, even though I get 3 boards in return. This is another reason for the delay in my update. I've been going over this board design multiple times to make certain that it is a perfect as I can get it before sinking the money into a first prototype run. Once the board is received, populated, and tested, I'll post pics as well as documentation. I have built this board to be a generic VME interface with surface mount LEDs on every single VME line, mainly for the geek factor but also because I figure why not... I'm already blowing half a kilodollar on the board. The board will allow me to use different CPU modules, perhaps an x86 or some other architecture, and just reuse my existing VME chassis, backplane, and peripherals. Or, if somebody else wants to take a stab at a homebrew VME board for a particular CPU, they will have a nice looking mainboard to start from.

The goals are thus pretty straight forward. For v1, I need to do code cleanup, documentation, and make the hardware a bit more tidy. For v2, I need to get this board sent off, then get it into my VME chassis and tested. Once that is done, I will start focusing on v2 and take suggestions from the community as to what peripheral to build next. I have great interest in building just about anything related to computers, and I am certain that whatever is suggested will serve as a learning opportunity for myself and others.

Additionally, I have noticed that hackaday.io has added a file attachment space for each project, so I will work on adding resources from my github.com account here locally.












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