The GIME-X project is a collaborative effort involving Gary Becker and myself. Gary heads up the CoCo3FPGA project and so has done a lot of work implementing the CoCo3 in FPGA form.
We had previously worked together on getting the analog board add-on for the CoCo3FPGA project produced, and when Gary approached me with the idea of working on an FPGA based GIME chip replacement I was delighted. Especially as this was something I’d already been thinking about, as well as it being something that would be really useful, as original GIMEs are not available to replace dead ones.
A 1987 version GIME
Gary is handling the Verilog, while I’m responsible for designing and building the hardware. I decided to go with a lower-end Altera Cyclone IV FPGA in the 144 pin QFP package for cost and ease of use/manufacturing. It was also a device I’d previously used in the CoCoVGA design, so I had some experience with it, and it was more than up to the task at hand.
So I designed a PCB that would plug into the GIMEs PLCC socket.
The board has the necessary FPGA, level translating buffers (5v to 3.3v logic), regulators, oscillator, flash, and DACs to pull a replacement together. In addition to the normal functionality of the GIME, enhancements are added, such as VGA video output and additional graphics modes.
We’ve made a lot of progress, going through a few revisions of the hardware until we had that part sorted out. At this stage we have a working board and configuration, and are refining the Verilog while testing it with various hardware and software working on making it as compatible as possible.
Artifact colors will be simulated on the VGA output for games that use them. I made the following video shortly after that was implemented.
Simulated composite artifacts
As we get nearer to completion of the GIME-X project ad prepare for production there are a number of things to consider to help it go smoothly.
So there you have it, an easily available and more economical solution for the PLCC plug.
Other additions to the design also seem appropriate as the project nears completion. For instance, an NTSC encoder and analog circuitry to support composite and s-video connections, as well as support for >512K memory expansions.
To these ends, I’ve revised the design for the next prototype boards, which you can see here…
Improved design with NTSC video and >512K support
GIME-X prototype (w/NTSC circuit), note the upper address support to the E2 ram board
GIME-X prototype, bottom view (PLCC plug solution shown)
Soon after this revision, some minor changes were made to the NTSC circuit, which has resulted in what I believe will be the final hardware for the GIME-X. Having reached this point, I thought it was time to see some images displayed on real hardware, showing off some of the new GIME-X video modes.
So I wrote a picture viewer app for the CoCo and a some tools on my MacBook to convert stuff. Here are some examples of the 640×225-16 color, 320×225-256 color, and 640×112-256 color modes. These are phone pics of the actual image being displayed by the CoCo on a VGA monitor. Click on the image for a larger version
Note: These are just random images taken from the internet and used solely for the purpose of testing this hardware. If any of the originators or rights-holders of these images object, let me know and they’ll be removed.
640×225 – 16 color GIME-X images on VGA
320×225 – 256 color GIME-X images on VGA
640×112 – 256 color GIME-X images on VGA
Another feature that we really wanted to add to the GIME-X was system acceleration. I’m very happy to be able to say that we were able to do that, achieving an enhanced ‘turbo’ mode which clocks the entire system at 2.86MHz.
This is a significant speed increase adding more than a million additional CPU cycles per second. Here’s a clip showing a quick comparison of the three CPU speeds supported; .89MHz, 1.79MHz, and 2.86MHz.
…more to come…