*** M E M O R U M ***

See anything different about the MFX board in the photos?

You haven't a hope in hell of getting the case back together?

Let's recap the clues:

You have a custom ROM that does away with Retro mode.
There's an FPGA dev board plugged into it that has a ribbon cable coming out of it, but I don't see where it connects.

Going to need more to go on, Martin, as this Sherlock is struggling.

Video Ram chip is missing?

gunrock wrote: ↑05 Mar 2024 06:47 Let's recap the clues:

You have a custom ROM that does away with Retro mode.
There's an FPGA dev board plugged into it that has a ribbon cable coming out of it, but I don't see where it connects.

Going to need more to go on, Martin, as this Sherlock is struggling.

Accurate, but nothing really of note there . . . .

The “custom ROM” is the latest firmware, as noted on the Firmware page
http://www.primrosebank.net/computers/ ... mfx_fw.htm

The changes to the boot menu and Retro mode are described in the corresponding manual update (1.2j
http://www.primrosebank.net/computers/ ... _usage.htm

The ribbon cable just connects to a USB Blaster for origramming the FPGA

acsi wrote: ↑05 Mar 2024 07:08 Video Ram chip is missing?

Now, that’s more interesting

So.... larger FPGA with more on-board RAM leading to a full TMS99xx emulation in the FPGA?

It is indeed a larger FPGA, it's a Cyclone 4 device EP4C6E which has 30k of onboard ram. That's compared to 13k ram on the Cyclone 2 EP2C5.

The original build MFX used the internal ram for the 80 column board memory, plus buffers for the sprite rendering on the VDP. The external chip was used for the 16k VDP memory. The other 16k external memory was connected, but not actually used for anything.

Bill then re-wrote all the video handling for the January release, that introduces all sorts of goodies including the USER VGA 2 mode 80 x 48 text screen and the 320x240 bitmap modes that make full use of the 32k vram. Since 8k of internal ram is also being used, the current MFX builds are using up to 40k for video ram

Building the January release code for the cyclone 4 board revealed a REALLY nasty surprise. The VGA display was awful**. It looked just like the original VDP output on the composite. There were VERY visible hum bars, no need for retro mode on THIS board!

As a potential FPGA alternate board for the MFX it was a non-starter.

However, not wanting to give up on it enturely ...

I tried removing the external ram and taking a step back to the original 2 mode video design which used just 24k I have got that running using the internal memory and the display is just as crisp as the original. And while it sort of works with the new rom, it's not really useable for anything other than VDP mode. Using the 80 column display requires the original 167 rom.

As a proof of concept, it worked. As a 2nd source board for MFX it's a step backwards



** The guy that designed it uses it in pinball machines, so it's never been used to output VGA until now. I tried a few simple board mods like adding more power regulation but that didn't help.

gunrock wrote: ↑05 Mar 2024 06:34 You haven't a hope in hell of getting the case back together?

Absolutely not.

That's where the PS2 keyboard interfacre really comes in to it's own That MTX is one Memotech altered in the factory to use eprom instead of mask rom. So I have an alternate set of eproms fitted** that has the keyboard tables patched to use the PS2 keybaord in Basic, as well as CPM, without needing the installable ptach.




* did you notce the non standard roms on the MTX ?

And why look at a different FPGA board?

Down to me I’m afraid . . . . .

I’ve had lots of problems with procuring the Cyclone Ii boards. There were shortages on the back of the Covid thing, but availability is improving. The biggest issue though is the variable quality of the boards from the Chinese vendors. Many of them have problems - mainly down to poor quality soldering of the FPGA onto the PCB.

I thought that as so many vendors had them listed that the board must have been Open Source at some point, so I tried to find the design files with a view to getting some fabricated myself. I couldn’t find those files, but did come across a guy (Ralf Thelen) who had cloned the design for his Pinball machine projects after having similar supply issues as myself.

Ralf took it a step further and added the Cyclone IV FPGA. Since the Cyclone II is prettty much EOL, I thought that I’d get a test run of boards made (in Memotech Red ) with a view to using them in MFX and sent one each to Bill and Martin for them to play with too.

Needless to say, the video issues were a disappointing surprise, but all is not yet lost . . . . . .