One chip MSX improvement project

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By spl

Paragon (1461)

spl's picture

11-03-2016, 14:46

"This listing was ended by the seller because the item is no longer available", http://www.ebay.com/itm/MSX-Bundle-MSX-Turbo-R-Modded-One-Ch... , listing has been cancelled. Good :)

By spl

Paragon (1461)

spl's picture

11-03-2016, 14:50

Anyway, any news on improvements for 1chipMSX? Last version is from 2014.11.24 and last Caro's DE0-DE1 core is from 2013.05.17... oO

By Manuel

Ascended (15600)

Manuel's picture

11-03-2016, 22:45

Um, a turboR in a 1chipMSX?

By hit9918

Prophet (2864)

hit9918's picture

11-03-2016, 23:11

TurboR is what is missing in OCM, the missing link in the OCM MSX3 story.

Quote:

I think the bus clock is 10 MHz (I wonder if that’s healthy for cartridges) but the CPU clock is 8 MHz or so.

how should an 8mhz z80 make the bus signals of a 10mhz z80.
bus = slot = zilog timing diagrams
would only be possible if it had the logic to decouple slot
but then instead slots 10mhz and cpu 8mhz one would make slots 3.57mhz and cpu 21mhz alias the missing TurboR.

I dont know how much cartridges work in practice, but 10.xx Mhz is 3x the compatible slot. and 2x the VDP dotclock.

what is the fpga mhz spec and what max z80 mhz does it make
the wiki doesnt tell. what mhz crystal does it have.
taking that EP1C12Q240C8N id from wiki, a 275MHz spec pops up in google.

By RetroTechie

Paragon (1563)

RetroTechie's picture

12-03-2016, 22:01

Manuel wrote:

Um, a turboR in a 1chipMSX?

IIRC, the Turbo-R hardware timer is already implemented in the 1chipMSX. So apart from a few Turbo-R specific 'quirks', additional ROMs and a much faster Z80, the 1chipMSX is already mostly there.

hit9918 wrote:

what is the fpga mhz spec and what max z80 mhz does it make the wiki doesnt tell. what mhz crystal does it have.

Original 1chipMSX has a 21.48 MHz crystal = nice base frequency for the VDP clock. But modern FPGA's can do internal multiplication of such clocks. Relevant quote from Cyclone device handbook:

Quote:

Cyclone PLLs provide clock synthesis for PLL output ports using m/(n × post scale counter) scaling factors. The input clock is divided by a pre-scale divider, n, and is then multiplied by the m feedback factor. The control loop drives the VCO to match f IN × (m/n).

Also there are many individual timing parameters for an FPGA. So a 275 MHz is just a 'random' number that may refer to the max clock rate of a counter implemented in it, or max rate at which some register can be updated, etc. It only gives a ballpark figure to indicate speed of internal circuitry.

For a Z80 implementation, that's mostly irrelevant. Many Z80 instructions take 4~20 clocks or more to complete. In an FPGA you can do a lot of operations in parallel, pipeline stuff, and do in 1 or 2 clocks what a Z80 needs 20 clocks for. That way an FPGA (like the Cyclone 1) can do a 50MHz+ Z80 equivalent easily (but you may have to sacrifice predictable timing).

Note that this is already done! See OpenCores projects NextZ80, Wishbone high performance Z80, and Y80e.

So it's more a matter of compatibility, or how to switch between 2 CPU's (if you want to keep fully compatible Z80 clone on board), FPGA Logic Elements required, and implementation details / software issues. Personally I'd be fine with a 20MHz+ fully compatible Z80 without any R800 specifics. Those few softwares that 'need' an R800 should be easy to patch.

By AxelStone

Prophet (2663)

AxelStone's picture

12-03-2016, 22:23

RetroTechie wrote:

Those few softwares that 'need' an R800 should be easy to patch.

In fact Illusion City is already patched and runs fine on 1ChipMSX at 10,76Mhz mode.

By spacemoai1973

Expert (96)

spacemoai1973's picture

12-03-2016, 22:33

Xtal is 80MHZ

By hit9918

Prophet (2864)

hit9918's picture

12-03-2016, 23:28

very good.
there is 21Mhz, there is a z80 core.
it looks like it is the usual thing: missing is the logic for turbo z80 + compatible slots.
"the R800 does not fit on the die" - no problem, turbo z80 is ok.

TR = turbo cpu + compatible slot
MSX3 = TR board + gfx 9000
In the OCM MSX3 story is missing just a little piece...

By RetroTechie

Paragon (1563)

RetroTechie's picture

12-03-2016, 23:40

hit9918 wrote:

In the OCM MSX3 story is missing just a little piece...

Yeah - a 'technology refresh': same general idea as 1chipMSX, but newer family & bigger FPGA. One that you can actually buy for a reasonable price. LOL! And USB keyboard / mouse support.

The Arcade Replay Board and Mist FPGA computer come awfully close though. And I'm sure it won't be long until other options like that appear on the market.

By KdL

Paragon (1218)

KdL's picture

26-04-2016, 00:01

Algorythms wrote:

@KdL

Hi, and thank you for all your great work with the OCM core!
A suggestion: Would it be possible to raise the ESE SCC+ ram to 2mb now that a couple of new games use more than 1mb?

only the ASCII 16K emulation could go to 2mb

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