Please note that the artifacts you see on the screen in some parts of the gameplay are due to the use of the board in a FPGA based MSX (I use one of those for development to avoid any damage to real vintage hardware).
If you are using ROM to test, you MUST use MGLOCM from KdL 3.6.1 delivery, newer versions of MGLOCM causes artifacts on V9990. Kim / ToughKidCst is the one responsible for that software but never had time to talk to him to debug this, perhaps you have, in the meantime, use older MGLOCM from 3.6.1 release of OCM-PLD, even if using with newer firmwares (3.7/3.8/3.9) it works fine
My SX-1 is from Oct 2018, so, it was produced about the same time as KdL 3.6.2. Hard to say what 8bits4ever installed for MGLOCM firmware. The Zemmix FPGA and SX-2 will almost certainly have the artifact unless I change the MGLOCM firmware.
MGLOCM isn't a firmware but a rom loader. You can use the one that was sent along KdL OCM 3.6.1 distribution with any firmware (i.e. 3.9.1) and then v9990 rom games work without artifacts 
My SX-1 is from Oct 2018, so, it was produced about the same time as KdL 3.6.2. Hard to say what 8bits4ever installed for MGLOCM firmware. The Zemmix FPGA and SX-2 will almost certainly have the artifact unless I change the MGLOCM firmware.
MGLOCM isn't a firmware but a rom loader. You can use the one that was sent along KdL OCM 3.6.1 distribution with any firmware (i.e. 3.9.1) and then v9990 rom games work without artifacts
Cool. Here's hoping these carts go up for sale soon.
I have the pleasure to say that the superimpose feature is now working on my prototype. However due to the challenges I had to make it work, and the differences in how RGB signals are exposed in the variety of MSX computers, I decided to release two versions of the board on GitHub: TRH9000 and TRH9000S
Great! I have noticed how requested this function is, so it's really good that you have managed to implement it. 
Also, good idea btw, I shall rename my variation to TRH9000D - for doomnoob.
The biggest challenge I had was due to some MSX computers not exposing the YS sync signal that is required to control the superimpose feature on the V9990. There are ways to derive the required signal for the computers that don't explicitly offer it on the connector, but as some computers do that and some not, the complexity to research and find out if your computer offers the signal, change/make cables, etc is not just for the normal MSX user.
You can understand more just looking for the YS signal on multiple MSX computers exposing RGB on the wiki article
https://www.msx.org/wiki/RGB_(8-pin_DIN_45326)]RGB 8-pin DIN 45326 - MSX Wiki
You will see that some offer it, some not, some offer in different pins, together with other signals, etc
Ah... yes, I noticed this early on while researching the fabled Passthrough as well - so I just simply opted to only go with adopting the official RGB din-8 connector, from the MSX2+ standard, and ignore the rest. You make me think about how to circumvent the issue though! ^^ By creating daughtercards for the daughtercard, haha! LOL! With the right design, we can decouple the Din-8 connector from the graphics-card, onto a socketable mini-board that contains the plug and some support-components, which will then have to be altered for a couple of different variations of the RGB-input.
That's a ton more work of course... but it would offload the worst thinking for the end-users - they would just have to keep check of which MSX-model they have, and get the corresponding daughter-daughter-card for their machine.
An added bonus, is that it would improve the durability of the Din-8, since that part can be unsocketed while inserting the cable - the smaller pcb in the user's hand will make it easier to control the insertion-force.
Then, the TRH9000 will have just one DB15 VGA/RGB 15Khz connector and will provide basically the same features of the traditional GFX9000. Important to mention that the new board is not using the Sony CXA2075 RGB encoder but a more modern Texas Instruments LMH1980 sync separator to form the RGB signal from the V9990 VDP. That change makes the board simpler and offers better video quality.
Hmm... that would not have been my preference - I feel that it's importsnt to offer something more, however small, when compared to the GFX9000 - otherwise, why choose the TRH over that?
That's why I put both a DB-15 and a SCART-output on the TRH9000D.
(Side-note: perhaps it's less confusing for the users if instead of letter-revisions at the end of the name, that we use number-increases? So, TRH9000, 9001, 9002, etc.)
The TRH9000S will feature two connectors. A DIN8 connector to receive RGB from the MSX computer connected and a DB15 VGA/RGB connector to output the resultant superimposed signal. Of course, there will be a way to allow MSX RGB passthrough or disable the MSX RGB input thus making the board behave like the conventional TRH9000.
So, there will be two versions on the GitHub moving forward.
A good idea. :)
Question - where you inspired by my implementation, with the Din-8 as a secondary/third connector, or was it just one of those no-brainers that people come up with when working on the same thing?
TRH9000 Status
I just updated the repository with the v1.0 revision (first release). I’ve been using the board for the past several weeks and the video quality improved a lot from the initial prototypes, but of course it can be improved. I tried to isolate digital from analogic, separate the oscillators from the rest of the components, use shorter video traces on the board, etc but there is still room for improvement.
If you are curious to see the v0.3 prototype in action, please check this video of a bad player (me) playing Life on Earth TRH9000 - The Yamaha V9990 based open-source video card for the MSX - YouTube
In parallel to the effort to improve video quality, I’m also working to fit the board into a conventional MSX cartridge case. We have access down here in Brazil to factory quality ABS cases and I’ve been using a laser to create cardboard simulations before making improvements on the real board and order real PCBs.
Some pictures below
TRH9000S Status
My initial effort to implement the superimpose feature was using a LT1675 specialized RGB mux from Linear Technology. That chip is great, but requires +/- 5V, something we haven’t planned initially on the board (we have just +5V). That forced me to use ICL7660 to generate the right voltages, plus another LMH1980 to separate the sync signals from the RGB coming from the MSX… you can imagine the board would never fit a standard cartridge with so many ICs…
Then Doomn00b had the idea to use a SN74CBT3257 mux from TI. Well… results were the same with both, but the board is just a lot simpler with just that chip that with the collection of ICs I was using.
For the TRH9000S I have ordered the second batch of prototype PCBs to play with the signals. The video quality is also dependent on the developments made with the simpler version. I tested my prototype in an Omega MSX2 with success, but still need to see it working on my FPGA MSX (even changing the output to 15Khz I couldn’t see the superimposed image).
To fit that version into a conventional cartridge I think I’m already touching the limits of what is possible with routing in such a small work surface. ????
Well, that is it for today… I’ll keep you posted.
Eyyy, glad to hear I had a positive impact! ^^
I've been thinking about the size... although I agree with keeping it as compact as possible (it's just so darn cool!) - I think we should accept that we're already breaking the standard by even doing openings in the casing for the connectors, to begin with.
If what it takes to make a good product is a bigger board, then we should do that - remember, engineering is the art of using compromises to solve a given problem.
Hi friends, boards arrived from JLCPCB and during tests I noticed a weird behavior when superimposing the image. As you can see on the picture below, I'm getting a weird noise on the image generated when superimpose is activated. The board is working ok, but the image just don't have the quality expected. I've changed the capacitor values hoping it is something with them, but that doesn't seem to affect the horizontal noise bars on the image.
Strange is that in some games that is almost not noticed, but with Battle Bomb for example it is very evident. Also it is located towards the bottom part of the image. The TRH9000 (without superimpose feature) also has that, but it is very subtle and changing the resistance we have for each color we can alleviate that easily.
Anybody with experience in video to shed some light?
