A flash cartridge downloadable from USB, a few days later.

As I indicated in my previous post, I had almost reached the end of creating my USB downloadable cartridge, but unfortunately, the USB protocol generates periodic activity on the USB bus, which is disrupts operation of my cartridge. This involves unplugging the USB cable once the download is complete. This was not the objective that I had set for myself, namely to leave the cartridge connected to the PC while being used in an MSX computer.

So I had to find a solution. In fact it is very simple, use two processors on the card. The first manages USB communication, the second manages loading the cartridge and providing data to the MSX bus.

Yes, two processors. As the entire software aspect is already developed, all I will have to do is manage the communication between these two processors to finalize the project. As in any case the cost of the additional processor is comparable to that of a DIP FLASH, this solution is not that 'absurd'.

And the result of my thoughts is this:

I must say that the result is quite clean. I still have to check the placement of the notches because on the previous version, I realized that the insertion into the case was slightly forcing.

Ah yes, I also added the possibility of choosing the slot in which this cartridge should operate. Like this, the 'concept' is complete.

A flash cartridge downloadable from USB.

Everyone knows the cartridge system of microcomputers from the 80s. The MSX, a machine from that era, is no exception to the rule.

When you don't know anything about this type of machine, and when you finally get one, the first thing that comes to your mind is to see how it works. And so to do this, insert a cartridge, if possible of games, obviously!

This is when the problems start. How to do today when MSX has been commercially dead for more than 30 years. How to find such cartridges. It is of course possible to find them on the second-hand market. But buying 10 cartridges to test 10 games, well, that's not really viable.

The idea came very quickly to see if it was not possible to have a cartridge that could be refilled on demand, by SD card or USB device.

The Carnivore 2 cartridge, which also offers extras, uses a FLASH card to operate. You have to be able to find a compatible flash card, which is not always easy. I was never able to use the one I bought. The FPGA was poorly soldered and the cartridge quickly became unstable.

Straight into the trash :-(

There is the MegaFlashROM_SCC+_SD. It's the only one I managed to use. But to use it, there is a whole procedure to follow which is boring. And if you don't do this every day, you will have to find the documentation each time to successfully re-initialize the cartridge and copy your new game into it. The least we can say is that this solution is not practical at all. In addition, you have to use utilities that are provided in the cartridge while understanding what you are doing. And when you don't know anything about MSX, it's not engaging!

There is also the solution using a USB device like a key. For this, the rookie-drive-nx cartridge seems ideal. But also, after reading the documentation, I have never been able to get a USB device to be accepted by this cartridge: frustrating.

There is also the SD 512 but given the price of my three previous purchases, I decided I was going to discontinue the charges. So I haven't tested it.

Because, in fact, my goal was to test as easily as possible an MSX board that I had just built, Sergey Kiselev's OMEGA computer.

I had been dying to get my Omega board working for a while now. Because I don't want to spend more on a specific keyboard, I took the time to develop a USB keyboard converter to the OMEGA computer. 

I have also made the result of my work freely available on Github at this address: https://github.com/sillycony/USB-keyboard-to-OMEGA-converter.

So... I was looking for a solution to make this machine execute something in a simple way. This is how the idea of ​​creating a cartridge that can be downloaded via USB came to me.

I don't know if this is the easiest solution at the moment because I'm in the design phase and it's not yet finished despite several previous prototypes.

But I know that once finished, the cartridge will be very easy to use. Simply insert it into the cartridge port of the MSX machine while also connecting it to the USB port of your PC. Dragging and dropping your binary file onto the cartridge, which will be seen as a USB key, will be enough to make the ROM for the MSX available in a few seconds.

If the final solution for my cartridge is not ready yet, I am posting about it now because I have almost achieved what I wanted.

But why is the current beta version not satisfactory?

Well it's very simple: because the USB protocol imposes regular requests from the host to the device to check its proper functioning. And it happens every few seconds.

And? Well, the response process requires the processor on the cartridge to respond ;-). And that takes time. Even if the processor used is fast, while it responds to the USB request, it cannot respond to computer access via the cartridge bus. Result: the MSX computer crashes! But, when the USB cable is unplugged, everything works as expected, as shown in the picture above.

I even planned the automatic RESET of the MSX computer while loading a new binary, so that it then restarts on its own on the new game, or new application. It works very well.

I therefore need to dissociate the USB bus management function from that of the MSX bus management. Because I don't use a FLASH strictly speaking, but the flash contained inside the processor. 'Small capacity' flashes in DIP housing and parallel addressing are becoming more and more difficult to find and more and more expensive. 

So I don't have this problem with a processor equipped with the desired amount of Flash. In addition, it makes routing the printed circuit easier.

The final cartridge diagram looks like this:

I know, it's difficult to read. It's just a screenshot. But we can notice two big circuits there. These are the two processors used. The one on the right is in charge of the USB port, the one on the left is in charge of storing the binary of the cartridge and presenting it to the MSX bus. 

This will cost a little more to produce than expected, but as the two processors are the same models, I will be able to take advantage of the quantity order to reduce the final price.

The software is ready and validated. All I have to do is implement each processor with its part and add a small communication protocol between them. The most 'tricky' part consists of creating a new printed circuit board with more components. But I think I can use the design of the current cartridge to facilitate this new implementation.

I must say that this is now the second project that I have carried out with a professional type process with all that this implies of prototyping, extensive testing taking into consideration a whole bunch of parameters including price, ease of realization, reliability etc etc...

I must say that it is a very enriching experience... When I think of what the type of job I had at the French university was, just a few months ago... What mediocrity!

UTC1122, AUTOMATION, RETRO COMUTING, MINIMAL COMPUTING.

Some improvements to the device's I/O circuit board. I also added a precision clock. I'm thinking of modifying the main clock program to use this precision clock.

GoWin FPGA & the Wichit Sirichote's µPF--1 clone : subject closed

This time, it's said. I close the topic 'µPF--1 clone'

Why? Because it works.

A few years ago, when I set out to attempt to replicate Wichit Sirichote's work in FPGAs, I developed a minimal system based on the sources of Wichit Sirichote. It had already taken me quite a bit of time to translate all the hardware onto a commercial FPGA board, then develop a personal board to accommodate an FPGA module. I found that it would have taken me too long to re-write a complete system based on poor quality of the source provided. 

And then, I wanted to test the GoWin FPGAs. When I say testing, I mean creating an FPGA board and then programming a complete system. That is to say also test the GoWin development tools.

Free advertising ;-)

After seeing that the small computer created 'seems' to work fine. I decided to attack what is the center of interest of such a small computer, namely the operation in step by step.

Until then, I had contented myself with re-writing the source of Wichit Sirichote to allow the manipulation of addresses and data as well as the loading of programs by serial link. So I missed the step by step. In terms of real learning of processor operation, step by step is extremely interesting!

It's quite interesting to be able to modify a program value almost on the fly, then to check the result by immediately restarting the program. That's the whole point of such a computer. 

It's a personal opinion, but I find it much more relevant than working on Arduino modules as a discovery of computing.

The system set up for step by step operation is based on an interrupt triggered after a certain number of pulses of the signal M1. Interesting and very functional system. On this point, Wichit Sirichote's source served me well.

So there you go, I have everything set up except the 'REL' key. I couldn't figure out its usefulness, even studying the provided source well. Regardless, it is now possible to write an entire program by directly entering the processor codes, or more simply by loading the program via the serial link and modifying the code directly on the keyboard, starting then stopping the program to check the content of processor registers etc etc...

Small example of a program loaded via the serial link:

The system is therefore validated. The GoWin FPGA used works perfectly. It is a success. I forgot, the serial link works perfectly, here at 115200 Bauds, and not faulty at 1200 Bauds as on Wichit Sirichote's system ;-)

In terms of FPGA resource usage, this is what it looks like:

Barely more than half of the resources in logic gates. I haven't implemented expansion port management, but it only takes a few dozen logical units. Not bad at all!

What's next?

I will now try to set up an HDMI output based on these Gowin FPGAs. Because I would like to develop a real computer with screen and keyboard on which it would be possible to choose the type of processor wanted.

This kind of machine has already been built, notably by Jeri Ellsworth in 2002. It's been just 20 years. It did not meet with much success while the retro-computing craze started to really emerge from the 2010s.

This machine may have come out too soon...

Stefany Allaire is currently recreating a whole range of computers on the same principle. You can visit his website c256foenix.com particularly with regard to its new C256 FOENIX JUNIOR, based on a 6.29MHz WDC W65C02S processor :

Free advertising ;-)

I am really impressed with the quality of his work...

[ 07-16-2022) Small update : And now the test with the IOM MPF-1P expansion board.

In fact, I knew that testing the connection of my processor board on the IOM board was going to pose a potential problem. simply because a number of signals used to manage the expansion port are also used for the JTAG programming interface. 

In fact it is not that complicated. All that is needed is to dynamically control the FPGA programming management system. Once done, the operation of the external bus is instantaneous. The connection of the IOM is therefore completely normal. I completed my little test program to turn on the diodes on the IOM board. It works without any problem!

GREAT :-)

The 'funniest' part of the story is that while I added some logical ressources to manage the expansion port, the GoWin software summary report tells me a 50% logical resources usage . It was 52% previously:

I could put two systems like this in the used FPGA considering only the logic resources. However, I wouldn't have enough internal memory for that...

[ 07-18-2022) Small update : For fun, I also connected the small printer, here the PRT-1P model to my processor board :

It seems to work. Why do I say 'seems'? Because I don't own thermal paper. So I can not check if the message is printed correctly. All I can say is that the printer responds correctly to requests made through routines present in the ROM integrated onto the printer board.

I have no idea where to get thermal paper for this machine. Occasionally, I'll try to find some...