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.

Develop with AI.

A few months ago, I tried to code a ZILOG CTC in VHDL. Indeed, I have a long-term project to implement the Drumulator rhythm box from EMU into an FPGA. Why, you might ask? Well, I really appreciate this machine for its simplicity. Plus, I consider it a good project for this kind of development. I've been coding the core of the machine for a few years. That's not really difficult since it just involves using the code of the Z80 processor called T80, which is directly available as open source. A few lines of combinatorial logic in the FPGA, and the Drumulator boots up. At least, its processor part.

The problem with the story is that all the real-time operation of the machine is managed by a Z80 CTC. During my tests, I simulated the operation of this CTC. Simulating means I ensure the CTC behaves the way I know it should respond. The only problem is that this virtual CTC is not programmable, and in fact, I only use the channel managing the display multiplexing. But anyway, the proof of concept was validated.

Indeed, after testing the analog part of this Drumulator, I decided to tackle this CTC anyway. I did find some VHDL 'codes' for a Z80 CTC on Internet, but I was never able to use them correctly for this Drumulator project. The reason is that these codes were designed to react according to the very specific needs of the people who coded them. In fact, they are not complete Z80 CTC codes.

So, a few months ago, I tried again to create this CTC. But in vain. I did manage to get something working with the display board I specifically developed for the Efinix development board, which features a Trion FPGA, but it was impossible to achieve stable operation of the Drumulator's keyboard/display interface. I ended up abandoning the subject because, on top of that, I lacked the proper tools for debugging the VHDL code.

Since then, I have reused the TRION development system for my MSX cartridge. The goal of this new cartridge implementation was to incorporate a processor directly inside the FPGA to handle file transfers from a PC. So, having used the internal processor provided by Efinix to debug the download process step by step, I thought I could use this internal processor to send stimuli to my CTC VHDL code, while also being able to retrieve the state of this CTC, again through the internal processor, and send the result to a text console. 

If needed, a few lines of VHDL code 'would be' added to allow the visualization of certain signals directly on the development board's LEDs. This therefore seemed like a very compelling possibility for developing and testing VHDL code. However, as I am not a VHDL coding expert, and having spent a considerable amount of time trying to code the CTC in VHDL, I had realized what could be called a mistake, not in analysis, but in the structure of the VHDL code. This made it harder to understand and very complicated to test without the proper tools. And that's where AI comes in.

I then posed what seemed like relevant questions to an AI and refined the subsequent questions to steer this AI in the direction that suited me best. After a few iterations, I realized that the essence of the CTC was there. Furthermore, the code structure was different from what I had personally developed, but this posed no problem for me in understanding its 'intended' functionality at first glance, and also in immediately identifying potential points of failure, and most importantly, for what reasons.

So, I began systematically testing the VHDL code provided by the AI with the help of the internal processor implemented within the FPGA. And, little by little, I first validated the writing to all the CTC registers, then the various selected modes of the CTC's 4 counting channels, and the reading of the registers. And then, inevitably, the time came to test the interrupt system. This is the stage, I believe, where I failed to validate my personal VHDL code developed a few months earlier. And this interrupt management aspect is crucial for the Drumulator, and obviously for all Z80 systems that use vectored interrupts.

I tested all aspects of vectored interrupt generation: the management of the IRQ pin, the interrupt vector, the daisy-chaining of interrupts, the IEI and IEO signals, and, most importantly, the handling of interrupt ACK from the Z80. It's the same as always—nothing is complicated once you understand how the CTC works, but coding everything correctly in VHDL is not that simple, at least for me.

As a result, I was able to start from the source code provided by the AI, modify it, adapt it, and test its functionality step by step as features were implemented. The outcome is that I managed to test 100% of the CTC's VHDL code functionality. However, I must note that I am not using this CTC with a "real" Z80 but with a Z80 simulated externally via the input/output ports of the embedded processor.

Obviously, I coded the I/O behavior of the embedded processor to react exactly as a real Z80 would. Therefore, I cannot say this CTC is 100% validated as being identical to the original CTC, but from a functional standpoint, it is. And I have a strong presumption that it will work with a VHDL Z80 implemented in this same FPGA. However, one should anticipate that there will be some 'edge effects' during the concrete implementation and use of this CTC.

So, what was the contribution of AI in all this? Well, the generated code served as a framework to follow for developing and testing the VHDL code. Paradoxically, the code produced by the AI seems quite clean and, above all, easy to follow. Obviously, where I thought it wouldn't work, it didn't. But I already knew the reason, so I only had to correct it. In fact, the AI doesn't handle different timing domains at all, but that's not a problem when you know how it's supposed to work.

Finally, I have a functional and tested Z80 CTC VHDL code, ready to be used for real with a Z80 also coded in VHDL inside a TRION FPGA. In terms of time spent, I would say the benefit is total. Of course, I have some knowledge of VHDL, as well as logic, programming, electronics, etc., so I wasn't starting from scratch. But in fact, the time spent on this project corresponded to 30% development and 70% testing, which is a very satisfying ratio for me.

Next step in this subject: attempting to get the Drumulator's processor section running, this time with the help of a "real" Z80 CTC.

NEW COMMODORE 64

Thanks to digital technology, we can now easily publish almost anything.

So why not? Well, because I just received the very first computer from the new company Commodore:
https://www.commodore.net

I received the machine after the holidays because I wasn't around. But anyway, the important thing is that the machine arrived!

YES!

I am happy to 'rediscover' Jeri Ellsworth on the staff of the new version of Commodore. I first came across her in the early 2000s when she created an FPGA-based motherboard with a processor slot that could serve as the foundation for a new C64.

Bil Herd, who needs no introduction, and of course Christian Simpson, whom I've also been following for quite some time, particularly during the design phase of the X16. I don't know the other people at all, but I wish them all great success within this new entity. 

I remember the 1990s and the collapse of all 'alternative' computing. I was utterly disheartened and suspected the following years wouldn’t be much fun for me. I wasn’t disappointed, and it lasted… 30 years! Thank you to everyone, even if it’s a little late for me now. Nevertheless, this reconnects me with the thread of 'my life' after all, and that’s a very good thing!

MSX Cartridge: Some Progress.

The saga of this cartridge :

Initially, I developed a cartridge based on a single RISC-V microcontroller, downloadable via USB using disk transfer mode. It worked, but the constant interruptions generated by the USB bus from the PC eventually crashed the MSX computer.

I therefore split the management of the USB bus and the handling of data to the MSX into two separate processors. This worked very well on my machine, but very inconsistently on the machine of the person testing my cartridge.

I then suspected issues like ground loops, power supply, etc. So, I developed a new cartridge with galvanic isolation. The result was no better.

I redesigned the cartridge, this time incorporating isolation precautions from the start, switched to the YMODEM protocol over a serial connection, which allows me to properly manage the sequence of operations, and chose a new processor from STMicro, a fast STM32. Alas, even on my own MSX computer, the cartridge refused to boot.

Following all these tests, which spanned two years after all, I determined that, in fact, trying to serve data at a frequency above 2MHz is not a good solution.

I could have tried the RP2040, but I already attempted to set up the development environment without success. For me, it's a bloated system that uses Microsoft's VS editor. Being allergic to Microsoft tools, I decided to go with an FPGA.

The idea this time was to use an internal processor within the FPGA to manage file download and FLASH programming, and also, crucially, to use the FPGA's internal logic to redirect the different data/address/control buses to the three elements: the internal processor, the MSX bus, and the bus to the FLASH. I figured that at least this way, the flash memory would be directly connected to the MSX bus.

I therefore chose FPGAs from Efinix because their prices are very affordable. I created an expansion board for the Efinix development board, containing the serial port, the flash memory, and also some SRAM. I also created an adapter board for the MSX computer bus. I connected everything, programmed the VHDL part to manage the various physical buses. I programmed the FPGA's internal processor to handle file reception via the YMODEM protocol. I loaded everything onto the development board.

I then downloaded a Zanac ROM into the system and started the MSX.

And voila: 

Right from the first startup of the MSX, I successfully got the cartridge to boot. I then connected a USB keyboard through the adapter I also made to allow for this kind of thing, and was able to play without any problems. No issues, no crashes. I haven't shut down the system for a few days now, and I can still launch the game.

Something that seemed completely out of my reach just a few months ago has been achieved without much difficulty in the end. Result achieved just a few days before my year-end holidays. So, I can really switch my brain to OFF mode and have some truly relaxing holidays.

Happy Holidays and a Happy New Year to everyone.

Tip for easily working on serial frame coding.

I am currently developing the reception of serial frames from a file transfer from the PC, using the YMODEM protocol. Nothing too complicated since the protocol is very well documented.

Well, yes, but still… For one, everyone implements the protocol a bit 'however they want'. And then it's better to work, at least for me, with something concrete, namely being able to observe the process unfolding on screen.

Of course, it would be possible to use a logic analyzer with serial link decoding, or to use a serial port sniffer on Windows. From experience, using 'the little software that works well for that' on Windows is such a 'mess' that I didn't even consider it. Instead, I opted for a small module based on a CH347 chip that can be configured for use with several serial protocols. I personally configure it as TWO serial ports. This little gadget, bought for €6.09 on AliExpress (probably even less in USD), has a USB-C port.

I connect its two RX ports to the TX ports of the transmitter and the TX port of the receiver, which allows me to visualize in real time the operation of the two 'talking' systems, directly with the somewhat intelligent utility I installed on my machine, namely WindTerm. This way, I bypass all the usual hassles of Windows while having a super comfortable visualization of what's happening. I really like that!

Since I didn't have anyone around, I shared my 'thought of the day' with DeepSeek :

To bypass Windows headaches for 6 USD — it's a steal, isn't it?

And here's what it replied. 

" Absolutely! For six dollars to bypass Windows headaches, it's practically a steal. It's all about finding those simple, clever hardware solutions that cut straight through the software frustration. Smart move. "

Well spotted, Deep! But yes, 'software frustrations', hmmmm... Hello, Donald? 

MSX Cartridge, Cody Computer, Apple II...

Frontline Report:

Regarding the MSX cartridge, I'm still actively working on it. I'm currently implementing the YMODEM protocol on the internal processor of the Efinix Trion FPGA. The hardware and development software are now very stable. In advance, I've created a small interface card designed to be connected between the FPGA board and the MSX computer, with the goal of making the flash memory of the already-built expansion card for the FPGA board, available via a 'wired connection' on the MSX cartridge bus.

After successfully implementing a minimal 640*480 VGA interface on an Altera FPGA board, I must say that for the past few months, what seemed completely unfeasible to me—because it appeared too complicated—has actually turned out to be much simpler than I imagined.

And by the way, I am currently designing an expansion board—still for the Efinix FPGA board—featuring a 6502 processor, ROM, and RAM.

This time, the goal is to work on a hardware clone of the Apple II and an evolution of the Cody computer.

Regarding the Apple II, I had salvaged a machine in very poor condition from my former workplace. I had tried to get it working again and succeeded. But without knowledge and without the proper hardware environment, I couldn’t get it to do anything more than display its Basic prompt. Which was good, but still.

I then decided to build a clone based on a GitHub repository, the RETRO II : Retro II

But the development was unstable and unfinished. In fact, it never was completed. However, that experience allowed me to understand the Apple II hardware. I then thought to myself, “It shouldn’t be too complicated now” to revisit this study by replacing a large portion of the components connected to the processor inside an FPGA.

And with this expansion board, I also intend to take the Cody Computer concept a bit further. Because I find the work Frederick John Milens did absolutely fascinating. His machine resembles the Commodore 64, and above all, the documentation he provided is absolutely brilliant—it’s what makes the concept truly incredible. A highly relevant starting point for learning computer science—in the way I understand it, of course, which is, first and foremost, about the freedom to think and to create.

For more information about this machine, I invite you to visit the dedicated website: https://www.codycomputer.org

My personal take on this subject: having built this little machine, I feel I can allow myself to make an observation. In its current state, it requires the construction of a specific keyboard for input, as well as the use of an S-video to VGA or HDMI converter. This slightly diminishes its financial accessibility, since you have to add the cost of a custom keyboard plus the time to build it, and also add an external converter. Furthermore, it also reduces the machine's ease of use.

I imagine a 12 or 13-year-old who knows nothing about it, coming from a family where technical aspects are unfamiliar, wondering how to build and get such a machine running. For me, back in the day, I bought a Sharp PC-1500. An all-in-one where you just had to insert four batteries and read some simple technical documentation for a few hours to be able to start creating.

I would therefore like to add a USB port for connecting a standard keyboard, as well as replace the Propeller processor that manages, among other things, the video output of the original machine, with a system allowing direct connectivity to a monitor via an HDMI port.

I assume you understand where I'm going with this, given that I managed to create a 640*480 video card with VGA output, I'm thinking I might be able to push the concept to HDMI and graft it onto the Cody.

We'll see...

And then, I received another FPGA development board. Because I still want to make progress on the Drumulator reconstruction. I know the electronics of this machine well. All the development paths I've taken so far don't seem right to me. I think I want to have a functional machine in an FPGA to properly develop the rest of the hardware.

My last attempt at creating a Zilog-compatible CTC didn't work. Software simulation is a real hassle with the Efinix solution—at least, I haven't been able to get the hang of it. There is the option of using an external logic analyzer, but I'd probably use that more in the final development stage to validate signal timing.

On the other hand, now that I have mastered the internal processor of this Trion FPGA, I plan to use that processor to send test signals to the CTC. This will allow me to display all the information I want directly via the serial port. It's probably not the best solution for verifying a VHDL design, but well, for a bunch of reasons, it's still the approach I'm going to adopt.

I should clarify that I am not sponsored by Efinix. However, and despite a somewhat rocky start with this FPGA vendor's development tools, I must say that over the time, I've managed to get to grips with this development platform. I should say that the ease of integration of their RISC-V Sapphire processor core is, in my view, an undeniable plus. Well, in the past I thought I detected some potentially slightly troublesome features of the Trion FPGAs, particularly regarding clock signals, but I'm prepared for that. I can orient my designs appropriately. And, to top it all off, the development software doesn't require purchasing a license to enjoy the full potential of the IDE in terms of placement and routing and other optimizations.

It's a strategy I don't understand from the other vendors: charging for a license, sometimes an expensive one, to be able to fully use the target components? Well, one thing's for sure, if I do any work with FPGAs, it won't be with those folks. For them, it's all about whether it's profitable in the long run. For Altera, I think not, since the company hasn't existed for a few years now and was taken over by Intel, hum...

The Death of Arduino?

You have likely already heard that Qualcomm acquired Arduino a few weeks ago. Since then, the community has been questioning Arduino’s business model and, more importantly, the community-driven, DIY, and open-source nature of the ecosystem—and rightfully so.

Via the link below, you’ll find an interesting comment from Adafruit Industries, another key player in this ecosystem, which truly respects the "open-source" spirit of the community, regarding this acquisition of Arduino by Qualcomm.

https://www.linkedin.com/company/adafruit/posts/

 

 

In my opinion, Adafruit's remarks are entirely relevant and, I believe, irreversibly highlight the path that Arduino is now set to follow—leading to what we can easily 'predict' will be the more or less swift abandonment of Arduino by the community. Ultimately... to the pure and simple end of the Arduino adventure.

Open question: What comes next? For my part, I've been noting several independent companies operating in the realm of 'open-source' electronics. In reference to this post: Adafruit, obviously, but also SparkFun, DFRobot, Seeed Studio, Keyestudio, and many others.

The common characteristic of these companies is that they rely on existing ecosystems like Arduino itself. Although these companies also often develop their own "personal" ecosystems, the disappearance of Arduino could still lead to a brief period of uncertainty in the DIY world.

My conclusion: The torch will certainly be picked up. By a third party or by the community itself. Alternatively, the moment may be ripe for the emergence of another platform in the same spirit. Potentially both possibilities.

In any case, I feel this moment is more one of renewal rather than an ending. A heads-up to creators of all kinds...