RISKY MSX Cart - Proof of concept.

[arkadiusz.makarenko]

I have started working on new project. After series of USB HID devices I had to change domain a little. As thanks to @terriblefire I own TFMSX, I decided to work on something targeting this platform. So I came up with idea to emulate EPROMs using RISC V chips.

RISKYMSXCart.png (117.05 KiB) Viewed 1005 times

Stephen shared with me PCB cart design, which was a basis of my PCB.
I picked up CH32V307V, It is RISC V chip, with 256K of flash and 64k RAM for prototype. General purpose chip with quite nice price tag of £3. I believe that cheaper version for £1.6 (CH32V303V) will be suitable as well.
My main goal was to emulate EPROM in any way possible. I managed to achieve this last night when I managed to load something.
Today I managed to optimise code to a level that I was able to load first 32k game out of it.

My next goal is to enable USB Flash support. Initially hardcoded with fixed filename loading to flash after pressing a button, next I will need to work on two way communication and MSX software to list files from USB flash drive and allow picking up file to copy to cart.

A big thank you to @NYYRIKKI for helping me understand MSX in general and pointed me to C library which will be great basis for my MSX software.

PXL_20241213_002547038.MP.jpg (220.54 KiB) Viewed 1005 times

[Maximilian]

Nice work!!!

[terriblefire]

Outstanding work

[arkadiusz.makarenko]

I can't make USB FS to work, at least in the Host mode. Need to check again if those chips even can work as host without oscillator. I assumed that they can as they are very similar to v203s, but I think I was wong. Or I need to configure clock differently.
Anyway there is still a lot of work I can do on this prototype like writes, memory mappers, SSC and few other things.
It will be at least a month before I will be able to respin new PCB.

[arkadiusz.makarenko]

YEY! It was USB FS clock configuration.
Long story short, V307 clock tree is far more complex, and requires different config for HSE and HSI clocks... If I went for cheap V303 I woudn't have this issue

I have USB working now

[arkadiusz.makarenko]

Next milestone reached.
I can flash rom cart from USB, to chip memory, and run it from the chip.
At the moment only once, but still quite a progress.
Next step: tidy up.

Todo
Figure out how to support writes
Implement Konami MegaROMs without SCC

[arkadiusz.makarenko]

After a little bit of a battle with timings on reads, I managed to implement Konami without SCC ROM mapper.
Next steps:
Control MSX reset
Reconfigure chip to support 288K Flash + 32k RAM, instead of 256K flash + 64RAM
Configure Fash Enhanced Read Mode
Konami with SCC mapper
ASCII 8k mapper
ASCII 16k mapper



MSX software to select cart to flash.
- List files from usb (first 20?)
- request load
- select mapper Abandoned

OR

mapper Autodetection ...
Manual mapper config based on extension

Try to move to IRQ approach. It is to release resources for SCC.

Add support for NEO Mappers.
https://aoineko.org/msxgl/index.php?title=NEO_mapper

New PCB with connected DAC and possibly some control lines moved to different gpio port ( to reduce needed reads from gpio - savings precious nanoseconds) - Some small touches like a button or two and connecting DACs
SCC emulation:
- don't know where even start...

[terriblefire]

SCC emulation:
- don't know where even start...

For SCC emulation i would start by implementing the 32 byte wave buffers and getting the ARM to play them with the DAC. possibly look at what emulators do in terms of interpolating that buffer up to something that the DAC can handle. Dont bother with volume control etc for now just try to get some sound out of it. I would expect it to look very similar to what is in an emulator.

SCC implementation.

https://github.com/libretro/fmsx-libret ... ULib/SCC.c

So really all you need to implement is SetWave (to interpolate/interpret the wave forms to your DAC) and SetSound (set the remaining sound attributes).

[arkadiusz.makarenko]

SCC emulation:
- don't know where even start...

For SCC emulation i would start by implementing the 32 byte wave buffers and getting the ARM to play them with the DAC. possibly look at what emulators do in terms of interpolating that buffer up to something that the DAC can handle. Dont bother with volume control etc for now just try to get some sound out of it. I would expect it to look very similar to what is in an emulator.

SCC implementation.

https://github.com/libretro/fmsx-libret ... ULib/SCC.c

So really all you need to implement is SetWave (to interpolate/interpret the wave forms to your DAC) and SetSound (set the remaining sound attributes).

After reviewing this code, now I am 100% certain that I don't have enough processing power on this chip left to do this level of calculations. Maybe with some kind of additional WAIT states (?) , but impossible in normal write cycle

Saying this, I already started looking at STM32H745
It is £15 dual ARM core 480Mhz. This would manage, but it is far more complex, and would force me to learn new usb lib.
It has massive flash, massive amount of ram, and D/A Converters. I think I have Dev board with this chip, so I can do some tests before designing new PCB.

[terriblefire]

After reviewing this code, now I am 100% certain that I don't have enough processing power on this chip left to do this level of calculations. Maybe with some kind of additional WAIT states (?) , but impossible in normal write cycle

Saying this, I already started looking at STM32H745
It is £15 dual ARM core 480Mhz. This would manage, but it is far more complex, and would force me to learn new usb lib.
It has massive flash, massive amount of ram, and D/A Converters. I think I have Dev board with this chip, so I can do some tests before designing new PCB.

I dont think you need to do these calculations inside a bus cycle. Just be complete by the next or next plus 1 top of frame. Remember this is an audio device and our hearing would never tell the difference.