This is the second update to the Rejuvenator project. Part 1 can be found here.
In the last Rejuvenator video I demonstrated how we successfully installed it (finally!) and played a demo that required 1MB of chip to run. And it played it flawlessly. Showing our board actually works was milestone #1.
A few weeks before that same time, the company we were working with to help reverse engineer the board pulled out of the project. It was a pretty major blow. But we soon identified and began talks with another firm - one that had reverse engineered other boards and had an excellent track record in doing so. Those talks are on-going and have been very productive. It's worth noting that they are not experts in Amiga hardware. They are Apple experts. But they are extremely professional and know what they are doing.
We agreed as a team that, before trying to recreate the board, we should attempt to read the PAL (Programmable Array Logic) chips. If we can't decipher the logic in the PAL chips and write them to new chips - and have my working board recognize them properly. This will be major milestone #2.
The PALs have very specific and custom equations and logic written into them that perform specific tasks on the board. If the PALs can’t be read, we can’t write them to new chips. And if that’s the case, the project is pretty much dead in the water.
While I was experimenting with my installed and fully functioning Rejuvenator board, what I didn’t realize was a tiny particle of battery acid had floated off the leaking battery and landed quietly on top of one of the 84 pins that house the Agnus chip. When I popped my Agnus out, the pin literally fell off like an old dried up leaf giving up on it’s branch for autumn. I couldn’t believe it.
Luckily, EzdineG volunteered to fix the problem. While he was doing the repair, he hooked up one of the PALs to his own personal reader. The results were not good.
What we need to do next is send the board/chips to another source and have a second test performed. If that second test returns with the same results, we will be at a cross roads.I've got my hands on Eric's Rejuvenator and tried to read the PAL's with a TL866A (as GAL16v8 and GAL20V8). It appears they're all protected, as all I can see are 11111111's when read.
We will have to determine, first and foremost, if the project should continue. It may still be possible to reverse engineer the PAL chips, but we'd be entering much murkier waters.
mr.t.guru:I would think the best bet would be to trace the pins of each PAL and identify which signals are on which pins. Then reference the original Commodore equations and create an approximation. Then use a logic analyzer comparing the original Rejuvenator PALs with the approximation could give a very good idea of what would need fixing. Be sure your replacement chips are the same speed or faster than the existing.
Another option I have been toying with is using an Arduino Mega to send every possible combination of inputs to the chip while monitoring the outputs and create a truth table which could then be minimized to the proper equations. It's tough to realize, however. The logic can get exponentially difficult to decipher once latches, flip-flops, and output enable equations get assigned and looped back into other equations. I think the 20L8 only allows for 5 or 6 types of latches, and there are so few product terms that it just might be possible. I'm currently working on this to decode some other 20L8, I have not had any success.
So, there may be a path here but it won't be easy. Fingers crossed a second reading brings better results.This is exactly what Charles MacDonald's PAL reader does. I have one here and used it a few times to dump PALs for use with MAME. The dump is pretty raw and has to be run through a program Charles wrote which creates the equations. Then that file has to be put into WinCUPL and the jed created. Of course at any stage the read/conversion can fail either in the hardware reader or software equation converter then you have done nothing except lost a lot of time.
Also, I was able to convince the previous owner of Expert Services and owner of the bare circuit board (the only one known to exist as far as I know) to sell it to me. So the bare board is now mine to do with as I wish.
Regardless of the success of our efforts with the PAL chips, there is a company I can ship the board to that can recreate it. They destroy the board in the process; they actually sand it down and analyze it layer by layer to create a perfect copy. We'd then have the GERBERs necessary to remake the board in the future if/when the PALs are deciphered. I am leaning strongly in this direction and getting that ball rolling soon. So if our efforts fail, perhaps some one else will be able to hit the milestone we might miss.