Commodore is....

 REBORN!!!

Christian ‘Peri Fractic’ Simpson is the new CEO

08/01/2025
 

 
Back to basics...

Over a decade ago, I invested time in learning FPGAs. At the time, I thought it was a good idea—and I was probably right. Back then, microcontrollers didn’t have the performance they do today, and replacing all or part of legacy hardware could really only be done this way.

I had bought an Altera DE2-70 development board. FPGAs were all the rage, and although prices had become affordable, they started rising again. Even that wasn’t enough for Altera to survive on its own, as it was acquired by Intel a few years ago. Now, Intel itself isn’t in great shape either. The swan song of American tech?
I considered using FPGAs until 2019...

when I discovered GoWin FPGAs, which were much more affordable than Intel's. But then came 2020 and COVID—and boom, GoWin FPGA prices skyrocketed as well. Once again, I was stuck.

Then came Efinix chips. However, while I found GoWin’s development software somewhat clunky, Efinix’s tools are, in my opinion, a complete disaster—unintuitive, slow, and prone to crashing. Whether it's GoWin’s IDE or Efinix’s, neither is a good tool for development. But then again, that’s just my opinion, and I’m not a professional in the field.

My Big Mistake:

Whether using GoWin or Efinix software, I stubbornly tried to develop entirely within their ecosystems. And, true to my habit of persisting in error, I spent months wrestling with these tools. While I managed to get decent results with GoWin’s IDE—though with far more effort than I’d have liked—my attempts with Efinix’s IDE ended in outright failure.

My approach was simply foolish, and here’s why. The learning curve and overall usability of Quartus (Altera/Intel’s development software) had been, by far, the smoothest for me. I’d built solid experience with it and gained a strong command of VHDL. And here’s the kicker: VHDL works flawlessly with both GoWin and Efinix FPGAs. See where I’m going with this?

Yep—the much less stupid strategy would have been to develop on Altera’s platform first, validate the project there, and then port it to GoWin or Efinix. At worst, I’d only have needed minor adjustments for the target platform’s IP blocks.

Better Late Than Never

That’s exactly what I’ve decided to do: go back to an "easy" development environment to build my projects, then port them to my final platform of choice.

Luckily, Intel still provides the necessary software for the DE2-70 board—version 13SP1—so I’ve reinstalled it on my PC. And compared to my decade-old machine, my current computer should compile much faster, making this "old" board even more practical to use.

Tackling Video Signal Generation Again

This time, I’m revisiting video signal generation. While the DE2-70 has multiple types of RAM, it unfortunately lacks SRAM. And since I want my FPGA projects to be as portable as possible, I need to avoid platform-specific IP blocks—especially those handling dynamic RAM (DRAM).

Luck Is on My Side

Because over the past ten years, static RAM (SRAM) has improved significantly in capacity, price, and access time, interfacing SRAM with an FPGA is straightforward—aside from the high number of electrical connections, but that’s manageable.

Since I only need a modest video interface (limited pixel depth and color range), I can now get by with just a few SRAM chips while still achieving good resolution and enough colors.

And here's the small expansion board I plan to build to provide the DE2-70 with enough SRAM for video interface purposes. I've attempted similar expansions before, but the results weren't satisfactory in terms of access time. I believe I now understand why - this time, I'm taking a different approach. 

Here's what the physical implementation should look like:

The GPIO connectors obviously won't be implemented on this side since the board needs to be plugged into the DE2-70's connectors. I've also added a small connector to enable SRAM loading from an external processor board - I remember not including this feature last time and struggling immensely when trying to use a Z80 processor embedded in the FPGA itself.

That approach made real-time debugging impossible, preventing me from running code step-by-step to verify the VHDL video interface behavior. Essentially, I had two potentially buggy systems in the same FPGA code - how could I possibly determine which one was causing issues? This time, I'm not repeating that mistake.

 

Drumulator clone with STM32 processors.

There are times, when you truly don’t know which direction to take. At first, I partially replicated the Drumulator's functionality in a GoWin FPGA. Later, I attempted the same adventure with an Efinix FPGA. That’s when I ran into the challenge of completing the machine—specifically, implementing the entire Z80 interrupt system in this Efinix FPGA. I didn’t succeed.

During this process, I realized that developing something "new" in an FPGA isn’t very practical. The reason? Well, there’s no real-time debugger like you’d find on any microcontroller. So, I tried using a processor instead and went with a very interesting RISC-V processor. Unfortunately, as I progressed, I realized I wouldn’t be able to fully achieve my goal this way.

Then, I came across STMicroelectronics' announcement of a new member of the STM32H5xx family. Looking at its specs, I noticed it was very similar to the previous RISC-V processor—but with every feature doubled: RAM, flash memory, and operating frequency. I figured it was worth giving this microcontroller a shot.

Then, after a period where I could no longer get STMicroelectronics' STM32Cube IDE to work properly on my Windows machines (dealing with installation crashes, missing packages, and other issues), I decided to try again with this new processor. I installed CubeIDE and CubeMX - miraculously, it worked perfectly on the first attempt.

So I embarked on this new adventure, building on the various tests I had previously conducted with the RISC-V processor regarding waveform generation. However, I decided to approach this as two separate projects: first developing the analog section for sound generation and processing, and then - if successful - completing the control panel.

After numerous iterations, here's what the analog board should look like.

This is a first draft. I haven't attempted to route this circuit yet. I may need to make some adjustments to the placement of certain component blocks. And even assuming the circuit works as intended, I'll still need to verify the audio quality - particularly how it handles (or fails to handle) the various interference patterns generated by the processor.

I'm not done yet.

The positive aspect is that with this circuit and the tests I conducted while designing my MSX cartridge (which uses the same processor), I should be able to implement waveform switching relatively simply. This approach eliminates the need for larger PCBs containing multiple memory circuits.

Well, having worked on multiple units of the original Drumulator circuit during repairs, I have to admit the final PCB is significantly more compact and uses far fewer components. It's nothing like the board in EMU's machine.

Of course, there's still the control panel to develop. But even that only requires a few additional elements compared to EMU's version - just some LED drivers, two keyboard multiplexing circuits, and that's about it...

UPDATE 08/01/2025

My Experience with EasyEDA Pro:

I tried using EasyEDA Pro to design the analog section of the Drumulator. After spending some time with it, I’ve concluded that this development tool is absolutely not for me—it just doesn’t suit my workflow at all. The limitations and its general behavior ended up frustrating me to no end. As a result, I’m going back to good old KiCad to redesign the board, with a few minor tweaks. The overall concept remains the same, but I’m changing how some components are physically laid out. Normally, I believe that fewer different elements in a system mean easier debugging and better reliability, but this time, I’m doing the opposite—adding more components to simplify things. Surprising, right?

Tech Rant: The State of Software & Forced Bloat :

And speaking of annoyances, I’m getting increasingly fed up with how systems and applications behave these days. The way they push—or rather, force—users to accept commercial nuisances is beyond frustrating. I’ve already stopped using Firefox except for certain sites that require specific resources. Otherwise, I never use Bing, and Opera and Firefox are now limited to just a few websites.

Unfortunately, I’m stuck with Android on my phone for now, but these so-called "updates" are just excuses to bombard users with checkboxes, tricking them into installing bloatware. And even then, some apps can’t be refused upfront—you have to uninstall them afterward. Needless to say, I won’t be switching to Apple. It’s the same nonsense, just worse and more expensive! This trend is spreading to more and more software.

My Solution? Linux + Minimalist Setup:

So, my plan is to set up a small Linux machine and keep my Windows PC strictly for development tasks. On Windows, I even use a portable browser instead of installing one. As for my phone, the only reason I’m still on Android is one essential app. The second I find an alternative, I’m switching back to my trusty Siemens B615! 

MSX FLASH cartridge.

I just received a few prototypes of my new FLASH cartridge for MSX computers.

In the past, I created several prototypes based on the copy/paste file principle under Windows.

This approach caused issues with the low-level connectivity of the USB bus, which meant that after developing the very first cartridge prototype equipped with a processor that handled all the operations, I had to switch to using two processors. That's when I created the second iteration of my cartridge.

With this second prototype, I was able to observe in situ all the transfer issues caused by the asynchronous nature of USB transfers. In particular, it's never possible to know whether a transfer was successful or not. Worse, there's no way to determine if a transfer is complete or not, hence the impossibility of controlling anything.

So, I had to change my approach and opted for a more reliable protocol. I decided to use the Ymodem protocol instead, which allows for full control over the sequence of operations. On Windows, I relied on the Hterm tool, as it provides a stable implementation of the Ymodem protocol.

I also chose a new STM32H5xx-type processor, which has more built-in resources than the RISC-V circuits I used before, greatly simplifying the schematic.

The result of this new design is as follows:

Now that I have the new cartridge in front of me—so much simpler than previous iterations—I have to admit I’m wondering whether I’ll actually manage to implement all the planned functions.

I also need to integrate a software reset system I’ve been designing. This last point is critical because it should allow rebooting the MSX computer without touching the ON/OFF switch.

Moreover, since the very beginning of this cartridge’s development, I’ve absolutely refused to rely on a configuration phase—for example, toggling between programming mode and usage mode by selecting an option at the MSX’s startup.

To me, it’s utterly unbearable to have to press a key within an extremely tight timeframe (inevitably shorter than the LCD screen’s video signal detection delay) just to choose a mode. The result? You have no idea what you’re doing. Frankly, this approach is just idiotic!

Now, the only remaining step is to port my earlier tests from the dev board to this final version. After that, I'll need to confirm the hardware implementation works flawlessly.

STM32 processors, in fact...

I mentioned in a previous post that I wasn't about to use the STM32 family of processors again. I had been testing with an STM32H5xx processor, using the STM32CubeIDE development software and its 'friend', STM32CubeMX, since for the first time in a long time, the software suite was working for me.

It's true that the new STM32H5xx processor family is interesting for several reasons. On the one hand, these processors are fast, they can operate at up to 250 MHz and, above all, some models offer 512 KB of flash memory and more than 272 KB of SRAM memory.

I then thought that this could allow me to develop a new version of the MSX cartridge that could be loaded via the USB port.

In my previous cartridge version, I used the principle of external mass storage. To simplify, the MSX cartridge behaves like a USB flash drive. Subsequently, the file recovered on a FAT12 file system type media, was recovered and copied in RAW format to the cartridge second processor.

This is what the cartridge looked like:

In fact the right processor retrieved the file through the USB port connected directly to a PC. Then sent the retrieved file directly in RAW format to the second processor which 'provided' the data directly to the MSX computer.

This system wasn't easy to develop for a number of reasons. Most importantly, file transfer from a PC is unreliable. Not because the data could be corrupted, but simply because it's completely impossible to know if the entire file has been transferred!

And that's not practical at all!!!

Additionally, the processors used were a bit more modest in terms of Flash and SRAM resources.

So, I wondered if it would not be relevant to try the adventure again on one of these STM32H5xx processors.

However, I had two 'problems' to resolve. The first is that I no longer have to use file transfer in the file system sense, but rather a transfer in the sense of direct byte transmission. So I chose to use a serial file transfer using the YMODEM transfer protocol.

The Ymodem protocol allows you to receive the name and size of the file, which can be interesting, but above all the transfer is done in specific blocks with possible CRC correction, which suits me very well.

The second problem for me is not having to use what seems to be something downright overly complicated on the system provided by STmicro (see my previous post) : the USB function of the STM32 processor. So, I decided to go straight for a small external USB/serial converter circuit.

This last point will also allow me to set up good galvanic isolation between the PC and the MSX computer.

In short, this change of direction should allow me to make the operation of my MSX cartridge more reliable. Because although I have never had any operational problems with my own MSX computer, it has happened that it did not work correctly on other MSX, without me being able to determine the reason for these malfunctions.

Here is what the first prototype of this new study looks like, based not on a RISC-V processor but on an ARM processor from the STM32H5xx family :

To summarize, this new version offers a faster processor, a more secure and controllable file transfer system, and better galvanic isolation.

I have already carried out some preliminary tests on a study board, namely transmission with Ymodem and programming of the internal flash of the processor.

Additionally, I should be able to install a more convenient status indicator system than the two original LEDs.

This new cartridge should also allow me to automatically reboot the MSX computer without using an external system. It should also be able to integrate different mappers for a total of 256KB of memory. Finally, my system should also be able to be updated using the same file transfer mechanism. I have already successfully performed code relocation tests on this new processor.

Transfer times should remain fairly short, given that I chose a speed of around 230Kbauds, which did not cause me any transfer problems during my tests. A full cartridge should therefore be able to be transferred in around ten seconds, plus the writing time in FLASH, which will also remain very low.

And so, I now think of using this processor in my study on the construction of the Drumulator type drum machine...

A few days later...

The request for a prototype PCB has been made. I'll then be able to work directly on a properly assembled circuit. This will already save me a lot of unpleasant surprises, especially those caused by assembling the processor by hand...

Sometimes...

We repair electronic machines for people who are often nice but from whom we don't hear anything once the machine is back on.

And then sometimes we receive a little gratitude indirectly:

https://www.starwaxmag.com/custom-page-detail/125836-tomska

Tomska thanked me in a Facebook post. That's very kind of him : 

The original post is here : Facebook

A thought for Philippe, who looks at my blog from time to time 😉

I love STMicroelectronics :-(

It's been a while since I've looked at this manufacturer's microcontrollers. The reason was simple: over a fairly long period of time, I haven't been able to install their STM32Cube IDE and MX development system without the installation of these tools crashing miserably.

And then recently, I got caught up in an ad promoting the benefits of the STM32H5. It's true: the amount of FLASH and RAM are interesting, as is the maximum operating speed of this circuit.

So, 'for a laugh', I tried installing the IDE and MX. Unbelievably, the installation went smoothly. I was very surprised. But anyway, let's move on...

I wondered if I would be able to produce the classic 'Hello World', namely the flashing of an LED, in less than an hour. To my surprise again, I was able to do so.

At this point you must be wondering where 'the wolf' is hiding?

Well in the USB my friends!

Yes, STMicroelectronics has abandoned the classic USB management, present in the CubeMX graphic configurator, to replace it with the USBx driver.

And what is this thing? Well, a driver that has to do with Microsoft and Azure, and more specifically Azure RTOS. YES!!!

Isn't that fantastic? Microsoft's mess right inside your microcontroller, and for free!!!

And on the ST page, the little explanation of what it is. Without more explanation than that, by the way. Hmm!!! Setting up a 'gas factory', just to implement a 'small' USB communication? I already had the opportunity to implement the MIDI protocol via USB on a small ST processor with the 'standard STmicro driver', a few years ago, with the initialization carried out by CubeMX. Well, all that is finished.

On the ST Github repository, there is also a little explanation that goes well:

Ah, but no, ST doesn't leave you alone in the desert, they provide a package, which cannot be integrated into CubeMX, to "ease developers' life by reducing efforts, time and cost."

I want well to believe them, but in reality, it means more like 'manage on your own' : 

I like it!

It's not today that I'm going to come back to the components of STmicro!!! I think I'll stick with my Chinese RISC-V processors. They're a bit more rugged than the STM32s, but hey, I've already spent a good amount of time working on using the USB port. I don't want to spend months and months on the 'skills upgrade' for the ST microcontrollers...

Well, I still have a blinking LED on my desk, driven by a 250 MHz processor. That's not nothing!

Drumulator : with RISC-V processors.

For now, I'm working on the analog output board of the Drumulator. After testing the feasibility of my concept, with the help of a few off-the-shelf boards, I'm starting to draw up the schematic diagram for the audio section of the Drumulator.

The schematic isn't complete yet, but there are already number of components.

This shouldn't take up too much PCB space, though. One of the dimensions will be dictated by the alignment of the audio connectors.

Drumulator : with RISC-V processors.

And meanwhile, I'm making progress on the subject.

And it doesn't have to be simple! My goal is to make it 'easy' and not too expensive to manufacture. The idea is to design a quality machine that has a good sound.

The options to consider, the best use of available resources, and other considerations mean that it takes a little time to develop. But in the end, I enjoy that moment when, after many development difficulties, I feel that the final solution is taking shape.

Rather than designing a test circuit and then going through the cycle of testing and modifying the circuit, this time I preferred to use already available development boards. Obviously, this makes the development look a bit DIY, but in the end, it goes pretty well.

To facilitate the development of the machine, I opted for a modular design. That is to say that for the moment, I am focusing on the analog part in order to start by producing the audio output board which will be easily connected to the operating core of the machine which will have to copy the operation of the original Drumulator.

So now I'm at the stage of creating the schematic. I'll have to make the board and then run the tests. This is a process that, despite the ease of having electronic equipment made today, still requires a bit of time. But there you go, the subject seems to be off to a good start...

The Cody Computer : processor board assembly

As a reminder, the Cody computer is a small machine that is, in absolute terms, could be considered no more interesting than any other project of this kind.

Over the past twenty years, hundreds of projects like this one, and probably even more technically interesting projects, have seen the light of day. To my knowledge, all of these projects quickly fell into oblivion. I'm thinking in particular of Geoff Graham's Colour Maximite II (https://geoffg.net/maximite.html) project because I followed this project for years, and then, nothing...

All information about Project Cody is available at this address: https://www.codycomputer.org

But then why be interested in Cody?

The main point that caught my attention about this project is the excellent documentation that the author has produced on his machine. 

Beyond the machine's own characteristics, some of which are unsuitable for me, this documentation makes the assembly, use and programming of the machine completely understandable. All the documentation is in a 'small book' pdf that can be downloaded from the project website: https://www.codycomputer.org/TheCodyComputerBook.pdf

Furthermore, Cody comes in the form of an electronic board that could almost fit inside a ZX81 case. But it is of course more powerful than a ZX81. Equipped with a 6502 processor, it would actually look more like a Commodore C64 with less complex electronics. So, I find that it brings together two interesting aspects, the ease of understanding of the machine, and the power of a Commodore 64. Interesting, right?

So I decided to build this small computer to judge how difficult it was to make. My latest experiment in this area concerns the construction of the Omega computer, type MSX, by Sergey Kiselev : (https://github.com/skiselev/omega/blob/master/Mainboard/images/Omega-Keyboard_and_Mainboard-1.1.jpg)

Omega

Assembling this machine is not complicated for someone with experience, but for a first approach, it is still a different 'story' than assembling Coddy's motherboard :

Cody

As you can see, Cody also contains four 'big' integrated circuits like the ZX81 motherboard. Indeed, Cody also contains 3 other small integrated circuits to solder, which does not complicate the machine further, given that there is no HF modulator to install. On Cody, it is a Parallax circuit that manages the video by directly providing the composite video output (CVBS).

In comparison, the ZX81's board :

Cody therefore looks very much like a ZX81 kit to assemble from the time without more difficulty, but with a more interesting result than the ZX81. So to assemble this little computer, I put myself in the mental conditions that were mine when I was a teenager and I didn't know much about electronics.

I obviously had the printed circuit board made at JLCPCB (that wasn't possible at the time) and bought the four main components, namely the two processors, the RAM and the I/O circuit. I already had the EEPROM. The bus driver, a 541 and the CD4051 were taken from my stock of more or less new components...

I assembled the machine, not with the help of the sheet, but by scrupulously following the instructions and the assembly chronology as indicated in the documentation. It takes barely more than an hour of work to achieve this result:

I almost assembled this board in 'brute force' mode. I didn't have the recommended 3.3V regulator. I put another one in CMS version. The resistors for generating the video signal are also not exactly those recommended. There are a few Ohms of difference. I even created one of the resistors by putting in series two resistors that I had, for a result very close to the original desired value. In short, I tried to make a clean assembly, but with certain tolerances of the type that a beginner could make.

I also didn't buy a original 'Prop Plug' to program the Parallax circuit, I figured the FTDI-style USB/Serial adapter would be enough.

After testing the board's power supply, and initially setting up the Parallax circuit and its EPROM that I programmed using the Parallax tools, the machine did not start correctly, or even did not start at all, and displayed some time parasitic characters on the screen: not a good sign and a slight disappointment. I thought it would start without any problem.

First thing, when programming the Parallax circuit with the Propeller Tool software (https://www.parallax.com/propeller-2/programming-tools/), I had a communication error message telling me that the communication was not going correctly with the processor (/RTS used as RESET signal). In fact, and after several tests, I realized that when acknowledging this error, the application was still programming the processor correctly. I was able to verify with the oscilloscope that I was getting a composite video signal at the CVBS output.

The way Cody is built, assuming the Parallax circuit was programmed correctly, and assuming the 65C02 processor was new and should work, all I had to blame was the 74HC541 bus driver circuit. So I replaced it with another circuit, also from my stockpile, and voila!

As you can see, I went into full DIY mode, with a less than rigorous assembly procedure, but still practicing quality welding, and the machine worked almost the first time. The initial malfunction was only due to a defective component in my stock.

This way of doing things, not entirely according to the rules of the art, allowed me to validate the high feasibility of assembling this small machine, even by a relatively inexperienced person. I expected this result, which is why I 'pushed the vice' to really assemble Cody in beginner mode.

Because there's nothing worse than demotivating someone from the start who doesn't know much but is eager to learn. The possibility of error must be present without it leading to an intellectually catastrophic disaster. This is why I particularly appreciate the approach of the author of this little machine.

And now? Cody doesn't have an operating system but programs itself directly in Basic. It's ideal for getting started in the wonderful world of microcomputing. I haven't written a single line of Basic on this machine yet, and for good reason: I haven't built the keyboard.

Personally, I don't find it very useful to build a specific keyboard for this kind of machine. Obviously, the look loses a bit if you use a standard keyboard but hey, that's my opinion. So I'm going to do what I already did for the Omega, I'm going to create a USB interface allowing you to directly connect a standard USB keyboard to Cody, I find it more practical. The user experience is more comfortable, especially if, as a passionate person, you start spending long hours programming on this little machine...

Drumulator : with RISC-V processors.

Well here we are...

First in a long series of iterations on building a Drumulator clone. As a reminder: after trying to create a Drumulator using FPGAs, I gave up following the time wasted on the last used circuits from the Efinix brand.

Additionally, real-time debugging is much easier with microprocessor tools than with FPGA tools. Well, basically, for the type of subject in question here, it ultimately seems much more relevant to me to start on a microprocessor basis than on an FPGA basis.

In addition, this should also allow me to offer more capacity for the machine envisaged, while retaining exactly the same characteristics, including the non-linear 8-bit sampling which gives all its charm to the Drumulator.

To begin this series of micro-developments, I will focus on the sound generator since, ultimately, it is this generator which is the heart of the machine.

On the original machine, it is a whole series of logic circuits associated with static RAM which manages this subject. Moreover, EMU calls this sound generator, a 'sound sequencer'. The goal here being to do the same thing but using the minimum number of circuits and the minimum number of electrical connections, I am therefore going with a converter whose digital data will be supplied by the SPI bus.

In the continuation of this development, I will also try the use of an SPI type wave memory, in order, again, to minimize the need for connections. All this will have the effect of reducing the cost and electromagnetic radiation.

So, for now, my very first test is to set up a reliable SPI link to the digital to analog converter.

I'm not going to detail the whole process here, but basically it involves generating an SPI bus with the characteristics expected by the audio converter. That is to say, the number of bits expected, the different polarities of the signals and the frequency acceptable by the converter, here 10Mbits maximum per second.

So I configured the registers of the processor used to match the needs of the converter. I even made the maximum frequency dynamic to always configure the maximum frequency achievable by the processor according to the configuration of its clocks, but while always remaining less than or equal to 10MBits per second.

The signals seem completely correct and, in any case, present exactly the programmed pattern:

u16  Data = 0x555D;

I will now tackle the generation of interrupts. In fact, the data to be sent to the converter must be sent a certain number of times per second. It seems to me that it is around 22KHz for the Drumulator. I'll look up the actual value later. For the moment, it is a question of generating the same SPI signals not inside an infinite loop in the main() function, but directly by interrupt...

Drumulator : with RISC-V processors?

When you want to recreate an existing machine, is it better to recreate the hardware to install the original software, or to create new hardware but with the need to also recreate the software system?

After years of various tests, I chose: I recreated absolutely everything.

I recreated the Drumulator hardware in a number of FPGAs. Since these circuits are very expensive, I changed FPGAs several times, ending up with GoWin FPGAs in 2021. However, these GoWin FPGAs have increased significantly in price after 2022, making these circuits much less interesting. After further research, I finally found the Efinix brand FPGAs.

It took me some time to get used to these new circuits. But I managed to implement the Drumulator processor core. Unfortunately, if the system seems to work well, a few moments, quickly, the display shows anything. Despite having tested the entire Z80 interrupt management system, I am still unable to understand what is happening. Especially since I took the VHDL source code that allowed me to implement this Drumulator in the Altera and GoWin FPGAs.

Seeing time passing without being able to get out of this impasse, I decided to abandon this way of doing things and recreate the machine from scratch. In fact, and to repeat a remark from a former electronics professor who told me in the early 90s, "you are really a guy from the 80s technos", that is to say that I am rather very comfortable with microprocessors, well I will use one or more small fast RISV-V type processors. They are really not expensive and allow to perform fast tasks, knowing that they are capable of operating at 144MHz.

I have already had the opportunity to make a timer compatible with the TMS1121/1122 in this way. Indeed, it took me a little time to make the software because, contrary to what one might think, it is not at all obvious to move from a type of operation imposed by the programming system of the time, namely assembler, to an advanced language of the C type. It is mainly a problem of structuring the code and data.

But hey, I got there.

Not to mention that the development software allows real-time debugging with display of variable, register and memory values, all in a very dynamic way.

All this is not possible with FPGAs and especially the associated software which are, at least for Efinix, very slow and not practical at all, from my point of view.

In addition, the idea being to create a system as simple as possible, with a printed circuit board as simple as possible. The use of these small RISC-V processors will allow me to synthesize the machine into several parts which will, therefore, be more easily modifiable or even upgradeable.

The heart of the machine being the sound generation sequencer, I will start by recreating this part inside a RISC-V processor.

The operating principle of this sequencer is very simple. A certain number of times per second, the sequencer compares a base register of a sound address, with the value of the end address of the sound considered. As long as these two registers are not equal, the sequencer retrieves the data from the current register, in fact the base one which is incremented at each reading, sends this data to the converter while selecting the assigned physical output, thus increments this register. The operation is repeated as long as the base register has not reached the value of the end of sound register. This is also repeated for the eight outputs in the same period of time. And so on.

The experiment here will consist of checking that I can actually perform all these operations in the allotted time, knowing that I want to use components operating on SPI bus so as not to have to route a large number of tracks on the printed circuit.

This means that I will use an SPI DAC but also an SPI type sound memory. I must therefore perform an initial SPI reading of the memory then an SPI writing in the DAC. This process must be repeated eight times in the same amount of time, all a certain number of thousands of times per second.

Will this be possible?

In principle this should be possible. The SPI buses will be configured at 10Mbits/s due to the characteristics of the SPI components. This will give a transfer possibility of one Mbyte or 500K words (of 16 bits) for each component. Knowing that the sampling frequency is a little more than 20KHz, 22Khz I think, the transfer capacity must be 22,000 * 16 (8 words in SPI reading and 8 words in SPI writing) or a transfer of approximately 352,000 words of 16 bits per second. We are well below 500,000. This should therefore work without problem, knowing that purely processor operations on address pointers are very simple.

To return to the long-overlooked policy of small steps, the first operation consists of configuring the SPI port of a RISC-V processor to allow it to communicate at around 10Mbits with a 12-bit audio converter.

For this I will take an audio board that I developed two years ago now, containing everything necessary for the development of the eight outputs of the Drumulator:

As for the development board, I will use a test board that can be easily found on the Internet:

I have already tried to do this type of operation with the DAC board using an ARM circuit from STmicro. But there is nothing to do, I can't get used to the development environment as well as the different ways of using ST libraries depending on whether you want to work at a low level, i.e. close to the hardware, or at a higher level. I really prefer simple environments and development software that is not too graphical, which requires you to program the necessary registers with full knowledge of the facts without potentially being 'fooled' by the development software. In short, with ARMs, I did not achieve a satisfactory result. I hope to achieve this with this RISC-V processor.

EMU : STOP!

Since my last post about trying to repair the EMU1, I've done a whole bunch of new tests. I also replaced a few integrated circuits. The result is that I haven't progressed one bit.

I still can't load the loading utility from the floppy disk. Whether it's from the actual floppy drive, or whether it's using the HxC emulator.

I now believe that I have carried out all the tests that I could. The problem in this story is that I absolutely don't know the loading program written in the boot EPROM.

It is not impossible, for example, that the motherboard must be correctly mounted in the machine so that information coming, either from the digital/analog conversion boards, or from the control panel, allows the program to exit a loop in order to actually process the data read from the floppy disk.

From what I have done as tests on the motherboard, I know that all the logic for shaping the signals coming from the floppy drive works. As well as serial reception by the SIO/2. Selection by a few PIO output ports also works. Finally, I know that the RAM does not have defective memory.

So I was finally able to test the signals concerning the triggering of DMA when reading floppy disks. And here too, everything seems correct to me. However, the machine obviously tells me that the data coming from the floppy drive is not reliable. I don't understand the reason.

However, the fact remains that the data bus signals are horrible! I also worked on this aspect, managing to obtain very square signals. However that wasn't enough, I always get into a loop trying to read the data without ever getting out.

So, given the time spent doing all these tests and the results obtained, it is high time to stop wasting it like this.

I reassembled the machine. I'm now opting to throw it into scrap metal because in its current state, it's worth absolutely nothing.

No final decision yet...

Regarding the FPGA of a Drumulator, I'll stop there too.

I twice managed to integrate the Drumulator's processor core into two different brands of FPGA. I have been trying the same thing on TRION type FPGAs from Efinix for months now without achieving anything usable.

In fact, right now I know the heart is starting well. It shows me the message 'bAd.' at startup, but immediately, by displaying anything.

This is all the more strange as the interrupt system works well since the message is displayed correctly. But afterwards, the processor seems to go 'I don't know where'. And this is not very easy to test with a standard logic analyzer due to the difficulties in triggering signal sampling.

In addition, I must add that the development software is a bit 'boring': not flexible and above all really very slow. This thing is a real pain, even with a powerful PC. So as in addition, the development tool tends to annoy me a little, and the pseudo-integrated simulation system is not helping the matter, and given the time I have already spent trying to integrate the heart of the Drumulator into this FPGA, I will stop.

Also, I don't know the intricacies of the system of this machine. In fact, it is extremely difficult to move forward when something goes wrong. Indeed, there is virtually no way to know for sure where the problem is coming from. After a while, this type of situation is simply no longer bearable.

The idea was to build a hardware environment compatible with the Drumulator in order to be able to run the machine system there. It seemed 'easier' to do. Observations made, I now say to myself that it would undoubtedly be less complicated to develop everything using equipment that is more practical to use.

I've been working a lot lately on small RISC-V microcontrollers. The development software, which was not very practical a few years ago, has been superbly improved in recent months. And above all, working in this way allows you to carry out debugging in real time. And that’s super interesting.

And as these small microcontrollers operate internally at 144MHz, this provides quite acceptable processing power for this type of machine. And after all, I did this to recreate a programmable clock whose behavior is identical to that proposed in the Texas Instruments TMS1122 of the time!

So I'm still a little sorry for this situation because these two projects made me consume a lot of time without achieving any result. Not to mention the psychological aspect of it, because it is not easy to persevere when there is no sign of improvement. It's even more difficult to abandon a whole job to start again with another method.

But hey, to move forward, you still have to make choices, at some point...

The positive point of all this was to realize that I have lost a progression methodology that I had when I was very young. I know the reasons of this degradation...

EMU1 : no real progress lately :-(

 In fact, I still cannot read the contents of the EMU1 boot disk.

On the other hand, I accumulate the validations of parts that have become or verified functional.

Basically, and following major problems of a really diverse and varied nature, I now know that:

• The SIO/2 serial converter is functional.
• The PIO is also functional on its new circuit support.
• the RAM is free of defects because I can check its operation with the small test program I created.

At this point, I don't know if it's the floppy drive that's the problem. So I put an HXC floppy emulator back into service.

And, good and bad news: the floppy disk still does not read, but, and this is the interesting fact, I obtain exactly the same result as with the 'real' floppy disk drive of the machine.

I was also able to find an image of a system disk for EMU1 on the Internet. I was able to check the content of this image to see that it is indeed an EMU1 image.

I can at least conclude with good confidence that the floppy drive part, real or virtual, is not to be blamed.

How to progress now?

By chance, and passing through Paris, I obtained two replacement integrated circuits which are used to extract the clock and data from the signal coming from the floppy disk drive.

I like to go from time to time to one of the last 'old-fashioned' component resale shops in Paris. Okay, it's not RadioShack but it looks like it:

I have already had the opportunity to talk about this store on my blog. Since then, the window has been somewhat redesigned

On the other hand, the interior has not changed and has remained worthy of the early 80s: a real pleasure!

The goal is to change these components:

I had already studied the signals provided by these two components a little and found nothing to complain about. This was confirmed. Their replacement by two new circuits did not change anything!

As a last resort, I removed the time base establishing resistor needed to separate the clock and data, and replaced it with a potentiometer.

This allowed me to check with the logic analyzer that the signals were correctly recreated, as well as to determine the operating terminals. I placed the value of this potentiometer in the middle of this area. So, from that side, everything seems okay too.

And now the question arises of what can prevent the correct reception of data from the floppy drive. I obviously tested all the signals to and from the floppy drive without detecting anything wrong. Although I noticed a small artifact with the HXC emulator, which should not exist, but I will not dwell on this phenomenon since the behavior observed is identical to that with the real floppy drive.

And there, a new question arises: how does the system recover the data from the floppy drive, to process it? Afterwards?

And yes, because in reality, the boot system does not process data on the fly. It collects them, places them in RAM then executes the program which, if I counted correctly, this time is approximately 8Kb and not the 1Kb contained in the boot ROM.

And this operation is not done by polling. I imagine the processor wouldn't quite be fast enough for that. This entire operation is done by DMA. 

So, assuming now that all the 'mechanics' of managing the floppy drive work and that the correct data is indeed recovered by the system, we must now check that the DMA system places it in RAM.

I had already had the opportunity to discuss the Emulator's DMA system. In fact, there are 8 DMA channels that manage the sending of data to the converter boards for sound generation. However there is a particularity, the first DMA channel is 'usurped' on demand by the floppy disk reading system thanks to the SIORDY signal.

I am now 'imagining' that if this system does not work, the data cannot be placed in RAM, and therefore cannot be executed. If the boot system thinks that things are going well and that it checks the validity of the data in RAM, it will inevitably find that things are not working.

This can be verified by the LEDs on the front panel which remain on or which go off depending on the type of error encountered when reading a floppy disk.

In fact, I have some problems there too. I actually find myself between the following two cases:

And yes, I hear the head moving neither twice per second, nor once every two seconds, but about moving less than two seconds but not twice per second.

But, with the SWAP LED off, I would tend to lean towards case B. 

That would suit me well, because a CRC problem is entirely possible in the event of an absence of data. In any case, I'm going to go with this assumption for now.

The next step is therefore to check if the DMA system is working well and that the data is correctly placed in RAM. I don't know yet how I'm going to carry out these tests. The adventure continues...

EMU1 : it's still progressing...

The last time I posted about the EMU1 motherboard refurbishment, I stopped at the detected problem of the system reset. In fact I was able to see that the new SIO/2 put in place of the original SIO/2 did not start and did not allow me to run my monitor program developed to test the onboard RAM.

While the original SIO/2 port #1 works fine, I realized that the 'new' SIO/2s require a bit more initialization time. So, I studied the RESET system of the board and connected the SIO/2 reset pin directly to the main reset system. This did not allow the SIO/2 to work properly. Obviously, if the system developed by EMU did not provide a slight delay at the processor startup, and this is most certainly the case, the new SIO/2 cannot start. And since it is the SIO/2 port #0 that communicates with the floppy drive, obviously, it can't work.

So I opted for a somewhat 'baroque' solution: I took out the reset pin of the processor in order to generate a manual reset whenever I want. This reset does not reset the other circuits on the board. Therefore, I can start the processor once I am sure that the SIO, the CTC and the PIO are correctly initialized.

The reset button is the left switch. I also added another switch to simulate the 'UPPER' loading switch on the EMU 1 control panel.

And of course, this time I got my monitor program to start correctly. The SIO/2 is therefore correctly initialized and configured. So I will have to study a global reset system a little more sophisticated than the original one implemented by EMU.

Finally, when I say that my monitor can now boot properly on the new SIO/2, it does not mean that the monitor works properly. And yes, since absolutely nothing will be spared on this board, now I sometimes get strange characters on my serial terminal emulator.

Of course, I first suspected a RAM problem. When I launched the DRAM circuit test, I got random errors. I then told myself that this was not credible. I went to look at the PIO. Because this is the circuit that is responsible for bank switching. So obviously if there is a problem on this side, it will inevitably generate problems. I was still a little skeptical because I had to change this circuit once to test another one, nothing more. And until now, I have not had any problems with my monitor. The problems appeared when I modified the processor reset. Another 'bad' lead not to follow?

And indeed, after some tests, I realized that the PIO was simply not powered. A contact problem on the power pin with the effect that the component outputs were navigating in the middle of 'nowhere', generating a totally random RAM bank switch. Well, I changed the circuit support.

Once this socket change was done, my monitor worked properly again. Fortunately I didn't have this problem during my phase of writing the monitor code. With the 'shitty' addressing of the ROM and this bank switch problem in addition, I might not have been able to validate my monitor and, in a fit of extreme anger, I could have thrown this board out the window. It happens!

To recap, the biggest problem with this board initially seemed to be the SIO/2 port #0, which handled communication with the floppy drive, which was no longer working. All my work and all my struggles were 'just' aimed at getting a working port #0 back. What a struggle to get to this point.

It was finally time to test the original code of this board. So I did, and... absolutely nothing happened!
No more unexpected start-ups of the floppy drive motor. Nothing at all happens!

Damn!!! Is this bad news? Well no: 'saved' (for this time) ;-)

I then looked at the machine's user documentation, just to confirm what I had already seen, namely that in fact the machine does nothing at startup, except light up a few LEDs, and waits for a press on either UPPER or LOWER, to start loading the data onto the diskette.

So I followed the EMU 1 schematic and ended up finding (and I guess what I determined is correct) the connections to make on the motherboard of the machine to simulate at least the UPPER switch. The references of the connectors on the front of the machine and the motherboard are different. So, deduction work is required.

So I wired a second switch to the small piece of study PCB, and rebooted the system.

Obviously, it would have been too easy for it to work. Once again, absolutely nothing happens. As I am starting to get used to it now with this machine, I started to check if the system was operational. Using the oscilloscope, I was able to see that the two integrated circuits that manage the multiplexing of the keyboards were correctly addressed. So, a priori, everything is fine on that side.

So I simply continued testing the signal values ​​on the input and output side of the keyboards. And I found something interesting. While the Y9 output of the IC125 circuit is high, 3 inputs on IC121 and IC122 are low. Logically, all the inputs of these two circuits should be high.

I tested all the diodes and found 3 simply cut and a fourth shorted. The result of all this is that overall the system sees a certain number of switches activated. So, I already don't know how the small boot system can react with this type of malfunction.

Well, all I have to do now is change all these diodes and see what happens. But, for once, I feel like I'm moving in the right direction...