At some point I dropped the scope probes onto the ROM board.. long story short, I've killed A15 on the CPU
No worries I thought, I got 2 other SEC boards.. neither of those work at all. So I changed the CPU on my original board, meters out OK, doesn't work either
One problem I have found is the CPU footprint seems a tiny bit smaller than the CPU which isn't helping.. its also possible as the PLD is under the CPU, heating up the CPU might have upset the PLD.
I will take another look at the other 2 boards tomorrow. Though its looking like I really need a PCB with both chips on one side of the board so I can solder them up easier. Will have to flip the bottom chip (PLD) and autoroute the hell out of it and hope it can squash into 4 layers. I also want to route a couple more pins to the CPU..
I did have TOS206 booting in 8MHz mode earlier, but I think the A15 short was causing the crashes.. I've not been able to make any progress as to why PLD ROM decoding causes the thing to go loopy. I don't get these problems with the vanilla 68000... I must have spent 50+ hours on it these past few days and I really have no idea why its acting up.
One thing which may fix the issue, is to switch to 8MHz when its accessing the bus, which is what I was doing before in the hope that solves the problem. Though as it seems to be some odd issue relating to fast-rom, I am not confident that will solve it. Its also possible the "as was" working SEC booster might have only worked due to fluke hardware tolerances. I have had it running months ago all day at 50MHz without crashing, but that was with GLUE decoding ROM. So "slow ROM" was in action there. I never thought "fast rom" would cause so much trouble with the SEC design.
All I can really lean to, is there is some odd bus conflict between ROM and DMA and the GLUE is in the middle of it all. While GLUE issues BR to the CPU, the CPU if its doing a fast-rom access, will tell the glue pretty much right away it can have the bus, and for some reason it causes the DMA to act odd. But its not just that as TOS206 fails to work at all, along with TOS102. So there seems to be multiple issues going on. I have tried delaying and re-syncing all the bus grant stuff, but I just find more and more spectacular ways to crash out doing that.
It begs the question if its even worth going with these SEC CPU's if the are going to be problematic like this. The PLCC 68000's can run almost 40MHz, while the SEC is 50MHz.. It might be time better spent abandoning the SEC series and go back to progressing with the V2.X series of booster with the normal 68000. BUT as there seems to be a GLUE issue with fast-rom, a 40MHz STFM V2.X series booster might not even work. Its actually put a huge spanner in the works
The only thing I can think of doing currently is making a DIP to PLCC 68000 adapter so I can plug the STE booster into the STFM and see what happens... saying that.. the STE booster should plug into the STF remake socket.. So I guess if that works, it would be a direction to continue in at least.