A2601 Page Up!

A2601 Complete View Running Donkey Kong

I’ve finished the first version of the A2601 project. I’ve created a new page giving details on the project, including several photos, screenshots, videos and schematics. Complete VHDL sources are released under GPL (including a novel 6502 core).

A really mindboggling issue that I needed to solve during last week was corruption of the FPGA configuration bitstream when the on-board Xilinx Configuration PROM is programmed with a design. Naturally, the A2601 board is setup so that the Configuration PROM will automatically configure the FPGA on powerup. However, it seems that, after this, if one tries to re-configure the FPGA using the JTAG interface, the configuration bitstream will become corrupt (in fact, Xilinx Impact will report a verification failure). Apparently, the only way to overcome this problem is to keep the Configuration PROM blank during development, and only program it with the final design when it is ready.

Ironically, I had already encountered this problem a few years ago when I was first working on the A2601 design. I had identified the problem then and worked around it. Too bad I forgot all about it and had to spend a few days figuring out the same things all over this time again…

I also worked a bit on adding PAL video output support to A2601. I did obtain some color images but nothing proper yet. The major hurdle here is that I am trying to obtain PAL signals using a NTSC crystal, frequency multiplied by 16. It should be possible in theory, but there is something obviously missing, still.

A2601 Running First Game

A2601 Rev B Running Keystone Kapers

Here is the A2601 board running Keystone Kapers in demo mode. At the moment, the game ROM image is stored in the FPGA, because I had some problems with getting the on-board flash memory to work. Once I solve those issues and add the MegaDrive pad support, the electronics side of the project will be complete. Then, the final item in the project will be preparing the case to fit the board in.

A2601 Board Populated

A2601 Rev B Homebrew PCB Assembled

A2601 Rev B NTSC Color Bars Output

I’ve (mostly) finished soldering the new A2601 board. The Xilinx Impact software recognizes the on-board FPGA and Configuration PROM through the parallel port JTAG cable, so I am able to download designs into the FPGA. Just for testing, I’ve uploaded a small design that outputs some NTSC color bars through the composite video port, and it seems to work fine.

It seems some more work needs to be done to get the A2601 FPGA design to work with the new board, though. It has been quite a while since I last worked on this project (judging from the dates on the files, almost three years), and during this time FPGA software (i.e. synthesis, simulation, etc.) has moved on. So I need to remember all the little bits and pieces and fix a few things here and there to make sure that the design works fine in the simulator again (it previously did). Once the design works in the simulator, it should be fine in the FPGA.

An Older Project Revisited: A2601

A2601 Rev B Homebrew PCB After Etching Top Side

Having made quite a bit of progress with UFE, I’ve decided it’s time to take a little break from it while I wait and see how recent developments in the manufacturing front pan out (sorry, cannot give details on that yet). So, I am now revisiting a never-before-released project of mine that is almost five years old now.

The project is an ATARI 2600 clone on FPGA, including 6502 and TIA cores in VHDL and dedicated PCB layout, all developed by me. The design fits in a 100K gate Xilinx Spartan 3E, and works quite well in the simulator. The PCB design contains the FPGA, resistor-ladder DACs for video and audio, custom joystick input ports and flash memory for storing ROMs. Few years ago I even built a prototype. It worked well, but unfortunately it did not survive, since my PCB-making techniques were not as advanced back then…

So, what’s new this time around? Basically, a reworking of the PCB layout that fits in a smaller case and contains a single input port for a Genesis/MegaDrive gamepad instead of custom-wired pads. I’ve ended up choosing MegaDrive pads because they are commonly available, very easy to drive and they contain the necessary auxiliary buttons (start/select etc.). I’ve already started manufacturing the board and the photo above shows the work in progress. Hopefully, all will go well and next time I’ll be posting working photos of the board…