Various early-year updates. MSX cartridge & Drumulator.

Currently, I am working on two major projects. 

On one hand, there's the development of an MSX cartridge based on an FPGA. After several attempts to create this type of cartridge using different processors, I decided to switch to an FPGA. The task is quite complex as it involves being able to download an executable cartridge file from a PC, program the FLASH memory, and then make it accessible to the MSX once the programming is complete. I have, of course, already built a functional prototype using an Efinix FPGA. The results are very promising. So now I'm moving on to the hardware production of the cartridge. I have made FPGA boards before, but they were based on GoWin FPGAs. This is my first attempt with an Efinix Trion FPGA.

For now, I have just finished placing the components. This may not be the final version. I haven't routed the traces yet, so if I can't arrange the tracks properly, I may need to reposition some components. Basically, here's what it might look like:

The advantage of this version over the older processor-based ones is that now I will also be able to implement different types of mappers, and there is a good amount of RAM available. In fact, if there is space left after routing, I will consider implementing a battery backup for the RAM. This could enable the development of specific applications. And most importantly, I hope that this time, given the chosen technique, the cartridge will work on more than just my MSX motherboard!

And the second topic is still my attempt to implement a Z80 CTC timer within these Trion FPGAs. The goal remains to successfully boot the processor core of the Drumulator in this FPGA. I implemented this part of the Drumulator in FPGAs a few years ago, but by simulating the CTC's operation—that is, by providing only the necessary IRQ vector for the display, without implementing the entire 'handshake' system during the Z80's interrupt handling phase.

A month ago, I decided to 'give it another shot' by asking an AI for an initial implementation. I got a project that, predictably, didn't work at all, but it greatly inspired my current code. After several days of trying to correctly implement the Z80's interrupt acknowledge sequence and the actual IRQ routine return, I finally have regular interrupt generation. For those who know, I now successfully have the passing of the interrupt vector, its handling by the Z80, and thus the clearing of the interrupt 'pending' status. At the end of the IRQ phase, the CTC correctly decodes the RETI, allowing new interrupts to occur.

All of that is perfect, but... well, the display of the emulated Drumulator still doesn't work.

That's where I am at the moment: trying to understand why the Drumulator isn't starting. I should eventually figure it out, especially since it worked flawlessly a few years ago with a pseudo-CTC.