Mega 65 CPC Core Wanted! Will pay in 6128 Pluses!!!

[zhulien]

Hi everyone,

I really really want to have a Mega 65 CPC core - perhaps even a 6128 Plus core.  Ideally with some of the normal CPC modern expansions built in - 4 mb RAM, 32 ROMs, x-mass emulation (m4 would be nice but unlikely possible without additional hardware), MultiPlay, Speak&SID, Digitracker, Playcity, AMDRUM implementations.

For whoever makes a good stable compatible Mega 65 CPC core open sourced (perhaps based on the Mister CPC Core), and lets me and others test it for quality control, I will give you a free working 6128 Plus.  If you implement much of those extra hardware wishlist, I will give you two free working 6128 Pluses.  If you implement the entire lot of my wishlist above, I will give you 3 working 6128 Pluses!!!

(note: just the 6128 Plus computers, with your choice of internal Zaxon USB drives or original floppy drives, no monitors or manuals or PSU etc... and no they are not like brand new, but good condition)

ps... If you earn 2 6128 Pluses - happy for you to choose a working 664 instead if you prefer (no monitor or PSU).

[zhulien]

BTW, I should be more clear the first person that makes such a core, not everyone who makes a core 

[SerErris]

Hi, that looks not like a very big endeavour ... however I would not undertake it without myself having a mega65. 

So i checked on the mega65 and see - regardless of current availability - that it is 800€ ...

So I am not going down this route. It is by far to expensive for the same like a MIST or MISTer. Obviously that is just it is too expensive for me. 

However the Mega65 team has created a bridge tool to port MISTer cores to MEGA65.

Start here:
https://github.com/sy2002/MiSTer2MEGA65/wiki
https://github.com/sy2002/MiSTer2MEGA65

Reading that, it should not be too difficult to create a CPC, however less flexible than the MISTer. So a CPC should not be a problem, an Amiga with AGA support and RAM > 1MB will be a problem.

[SerErris]

Ah, researched the MEGA65 a bit.

One of the main issues of the MEGA65 is, that they do not have SDRAM like the MISTer has. You do have 1.5MB of internal RAM (actually directly in the FPGA) and some 8MB external ram, but with very bad timing - not suitable probably even for the slow CPC demand.

That RAM is not fully available - because ROMs are going into the same space. So we need the RAM (lets assume 128kb for now) and ROMs (lets assume 16x16kb=256kb). So you will be able to emulate 512kb ram expansion, but not 4MB. Even a 1MB would potentially fit.

ROMs.

Here we get into a real problem. ROMs are only supported on the MEGA65 if they are compiled into the code of the core. So you cannot load them from SD-Card for instance, like the MISTer does.

What is the implication?
You need to define a new core for any variant of CPC ROMs you want to have. This is not a problem if you know how to compile the core, but it is not something you want to do every day and if you do not know you cannot put in your own set of ROMs.

So in essence. It should be no big issue to implement a 6128 (maybe even Plus), and even 512kb to 1MB Ram expansion. But flexible ROM selection (e.g. adding your own, exchaning AMSDOS with PARADOS etc), will not be possible with that approach. It would require multiple cores.

[Prodatron]

Maybe that's a stupid question, but can't you just load e.g. a default file with 8x16K as ROM into the internal RAM during booting and keep it read only?
If you want to swap roms, you just change the file and reboot.

[andycadley]

Yeah, that's what I'd have thought. You'd need to be able to dynamically load "ROM" contents to be able to support the Plus, even if you're just faking it with some RAM the system never writes to.

[SerErris]

From what I understand (and that can be still wrong) there is currently no way to load files as ROMs into the MEGA65 at runtime.

This is actually one of the things that is difficult to manage.
The RAM in the FPGA itself cannot be accessed from outside. Only the Core itself can access it. That is also true for the ROM that is just placed into RAM areas and preloaded on core load time. The next issue arrises from the fact, that the Artix7 core has no CPU next to it (e.g. ARM or anything), that can do some work or help interfaceing etc. This is one of the main differences of the MEGA65 to the MISTer. MISTer is using a Cyclone V core that has two ARM cores right next to the FPGA matrix, So you have both running. The FPGA runs just the core, where the CPU runs the MISTER system and all the stuff around.

So you cannot load anything from the SD card that is actually a ROM itself. The reason is, that the core would need to execute it and the cure is actually a 6502 CPU or a Z80 CPU that has no clue on how to do that.

To be clear the System still can access SD cards as floppies or such things, but that is the system internally getting an emulated "floppy" and then useing the sdcard for it. But that is a different thing than loading dynamical ROMs from the SD card at startup time.

I cannot see how they want to overcome that limitation of the Mega65 design.

[SerErris]

BTW if you want to have something like the mister, look at this:
https://github.com/ChinaQMTECH/QMTECH_Cyclone_V_SoC_KFB_With_Dual_SDRAM
https://www.aliexpress.us/item/3256807184157012.html?gatewayAdapt=glo2usa4itemAdapt

This comes at a price of $131 and already includes 128MB SDRAM, that you need for most cores.
This will be fully sufficient to run any MISTer Core and with the additional analog board you will get all the required output options. Add a USB board and you have the full MISTer experience.

All of that place into a new AMIGA case or an old one and put in a normal USB Keyboard and you are ready to go. 

I am not saying that the MEGA65 is a bad project. But it seems to be really focussed on the C64 series of computers. They did not have the ROM issue and that is fine. However esp. with the large collection of ROMs on the CPC, that is not very flexible and at the same point in time comes with a hefty price tag.