Retro Computing via FPGA

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Tom Szolyga

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Oct 8, 2021, 3:13:59 PM10/8/21
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I am interested in retro computing using a FPGA.  The MISTer FPGA project uses the Terasic DE10-Nano board along with several expansion boards.  The FPGA chip is a Cyclone 5 which has 110,000 Logic Elements and two ARM 9 cores.  There are a "zillion" CPU cores to implement microprocessors.  

It seems one could have one board set to implement most any retro microprocessor system by simply loading a different CPU core.  In fact the Cyclone 5 could implement a system with 10 independent Z80 microprocessors.  Such a thing would be hard to build with original chips.

Thoughts?
Tom

Alan Cox

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Oct 8, 2021, 4:14:01 PM10/8/21
to Tom Szolyga, retro-comp
On Fri, 8 Oct 2021 at 20:14, Tom Szolyga <tszo...@pacbell.net> wrote:
I am interested in retro computing using a FPGA.  The MISTer FPGA project uses the Terasic DE10-Nano board along with several expansion boards.  The FPGA chip is a Cyclone 5 which has 110,000 Logic Elements and two ARM 9 cores.  There are a "zillion" CPU cores to implement microprocessors.  

It seems one could have one board set to implement most any retro microprocessor system by simply loading a different CPU core.  In fact the Cyclone 5 could implement a system with 10 independent Z80 microprocessors.  Such a thing would be hard to build with original chips.

I have mixed feelings having come from FPGA to actually building hardware. FPGA does let you build things like physically clock accurate emulations and deal with awkward timing constraints on interfaces very well but software emulation is faster (Will Sowerbutt's SocZ80 FPGA is 120Mhz, Z80Pack on a single core of a modern PC is about 20 times faster than that FPGA) and far far easier to work with. With some of the newer processors that are multi-core and have things like DMA and IO engines it's also no longer the case FPGA has a monopoly on the interface stuff either.

The bigger ones are also a pain to interface as they are 1v8, the smaller are 3v3 which isn't so bad.

There are some interesting systems using it - like MISTer,  ZX-Uno, and the ZX Spectrum Next, as well as hybrids like the ZX Evolution which is a real Z80 processor with FPGA doing the I/O and the other logic so you get an accurate CPU.

Alan

Mark T

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Oct 8, 2021, 5:18:24 PM10/8/21
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It might be worth taking a look at Grant Searle’s multicomp, I think it uses a cyclone IV, but could probably be adapted to any other similar or larger FPGA. I have had it running on a sainsmart development board, not enough internal ram for cpm, but was able to get a simple sdram interface running using the external sdram of the development board.

Dylan Hall

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Oct 8, 2021, 5:29:09 PM10/8/21
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You might want to look at the following:


It’s a 16 core z80 system on a high end FPGA. A fascinating read. 

Dylan 


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c f

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Oct 8, 2021, 7:40:27 PM10/8/21
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I think where FPGAs shine is getting to play 'fantasy computer architect.' As a professional computer architect I'm extremely biased, but I get much more joy out of building things in FPGAs than software simulations. For hobby work the biggest question you're trying to answer is "What is the fun part?" Carefully architecting around the resource constraints to cram a 256-core Z80 into an FPGA (and then trying to see how far you can push the clock speed!) sounds like a great time to me. If you're just in it to finally beat Zork, a software simulator might be way quicker and more fun. It really just depends on what your goal is. 

-Chris


rwd...@gmail.com

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Oct 12, 2021, 1:09:29 PM10/12/21
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I'd love to see an FPGA implementation which fully supports ROMWBW out of the box, and handles at least 4 serial ports. Not sure that Mister is the best option for retro cp/m as it appears to have limited serial port handling.
It would be good to make  it on an rc2014-ish board to support additional rc2014 boards, perhaps to implement memory as well using an existing memory board.

Also you might find the muellerk (Kurt Mueller) version of multicomp a good start as it has the GSX graphics implemented.

Several people have tinkered with multicomp on Mister but I get the impression that interest in development fades before a fully debugged version is available.  I was reading  up about mister but theory only as I have no hw budget yet.

Richard

joseluis...@gmail.com

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Oct 13, 2021, 2:15:36 PM10/13/21
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Hi all, you will find many Multicomp FPGA projects at retrobrewcomputers.org (builderpages section). I recommend Rienk Koolstra´s mc-2g-1024 Z80-CP/M implementation based on the Altera Cyclone II and you can take a look at my own one (Positron) based on a Xilinx Spartan 6. These systems can be easily adapted to handle 4 serial ports.
A suitable Cyclone II or Cyclone IV dev borad can be found at Aliexpress for USD 25 to 35 (the basic ones without displays and switches are preferable as they have more free GPIOs).

Richard, adapting the Multicomp architecture based on Grant Searle´s design and ROM, to run ROMWBW is in my project backlog. I recently opted for an early retirment at my dayjob, so I´ll have more spare time as I finish the wife´s endless list of -critical- home repairs and improvements ;-)

Cheers, Jose Luis.

Tom Szolyga

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Oct 13, 2021, 2:55:14 PM10/13/21
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Land-boards has an adapter that provides all the circuitry Grant Searle suggests to use the Cyclone II EP2C5 board with Multicomp.  
There is an option to order a thru hole or surface mount version of the board.

Richard Deane

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Oct 13, 2021, 6:01:53 PM10/13/21
to Tom Szolyga, retro-comp
Thanks for the update; for us UK/EU people we have problems if the vendor doesn't handle import and VAT - we get hit by extra handling charges. Land-boards doesn't handle it, neither does Tindie. Also the US shipping tariffs are high.

The Land-board designs are not free so I can't send off to JLCPCB in HK where they nicely handle VAT & Import; they and Ali-express for components have low postal rates.

I have the retrobrew Cyclone II and IV boards and a Land-Board  EPC4 kit.

Don't forget to handle both 25MHz and 50MHz  boards (blue and green).

I will happily volunteer to beta test. I have Quartus 13 & 20 on several machines - v20 is quirky - sometimes it finds the usb-blaster, sometimes it doesn't. 13 is for max 7000 and cyclone II, 20 is for cyclone iv.

Richard



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