New FPGA-based MSX

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By George.rm

Supporter (13)

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17-04-2018, 23:21

Zett, current estimates are at R$700-800 (Brazilian Reais, BRL), no idea about shipping to Europe.

Hardwaremaker, there is no discrete logic on the board save for the dual inverter gate used to run the oscillator

By Rataplan

Master (207)

Rataplan's picture

17-04-2018, 23:56

Nice work, slick pcb! Stupid question maybe, why is MSX2 in the MSX2 compatible logo reversed?

By George.rm

Supporter (13)

George.rm's picture

18-04-2018, 05:29

I didn't want it to officially say MSX on the board itself, as
1) it technically isn't fully compliant to the standard (but close)
2) trademark ownership is cloudy, but definitely not mine, nor am I licensed to use it for commercial purposes, so...

By hardwaremaker

Master (176)

hardwaremaker's picture

18-04-2018, 10:47

George.rm wrote:

Zett, current estimates are at R$700-800 (Brazilian Reais, BRL), no idea about shipping to Europe.

Hardwaremaker, there is no discrete logic on the board save for the dual inverter gate used to run the oscillator

If the components that I asked for, doesn't present in the board. Are they implemented in the FPGA? If this is so, you can't write the OCM firmware directly.

By RetroTechie

Paragon (1445)

RetroTechie's picture

18-04-2018, 17:30

Very nice work indeed! Cool Smile

George.rm wrote:

It will be compatible with KdL's OCM-PLD.

Do you mean the same FPGA pins are used for same function? If so: doesn't that complicate board routing a lot? If not (re-compile of OCM sources needed), then not much of an issue to re-arrange some functions. Like FPGA pin use, or other items where desired.

gdx wrote:

If you can also improve the sound mixing, do not hesitate!

Better yet: include a small 2-channel A/D converter, put cartridge slot audio signals in there with minimum filtering on the input, and do mixing in the FPGA logic. That way it's easier to fix/enhance mixing later. Or make it programmable through some I/O port, provide a hotkey or whatever.

By hardwaremaker

Master (176)

hardwaremaker's picture

18-04-2018, 18:13

OK, sorry, the OCM don't uses the 74HCXX IC's. Only the Zemmix uses them.

By zett

Champion (426)

zett's picture

19-04-2018, 10:40

that is not a bad price for a board like that. what fpga do you use on it? is it the same as all befor or is it a better one? becourse of the possible future?

By Grauw

Enlighted (7321)

Grauw's picture

19-04-2018, 12:14

George.rm wrote:

The first revision uses an EP1C12, but this is quite probably gonna change for future versions.

By George.rm

Supporter (13)

George.rm's picture

19-04-2018, 22:09

In time: BBcode isn't working properly here, so sorry for the sloppilly-written replies.

RetroTechie, yes, pin functions are a 100% duplicate the ones in the OCM for the current version. This'll change if I move to another FPGA, and I'll pass the changes to KdL so he can merge them into the code, should the project ever go this far. As for the routing, it didn't pose a problem. All was done by hand with no autorouting steps, from the component footprints up.

As for the variable mixing thru an A/D, the OCM code already mixes the sound sources implemented in VHDL variably, I guess adding an A/D could be done. My only worry is the amount of pins consumed. I didn't wanna start multiplexing stuff, to be honest.

By RetroTechie

Paragon (1445)

RetroTechie's picture

19-04-2018, 22:46

George.rm wrote:

I guess adding an A/D could be done. My only worry is the amount of pins consumed.

There must be some A/D converters with a serial output. Maybe using a bus like I2C or similar. Which uses like what, 2 signal lines or so? Say you find a 2-channel A/D chip with 16-bit resolution (not that you need that much, really Tongue ), and those channels are sampled at 'CD quality' 44.1 kHz, that gives a 1.4 Mbit/s serial stream (give or take some overhead). Kind of like an MSX-Audio or OPL4 external DAC but in reverse direction. Should be easy to handle by an FPGA, and if resolution/sampling rate is lowered, bitstream could even run at lower rate.

I could do a search for suitable IC's if anyone wants to have a go at that. Main advantage would be that it moves (some) difficulties with analog I/O circuitry into the math / FPGA coding domain where it -most likely- is easier to handle.

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