Any requests for an 8-bit computer?

lawrie 2020-07-02 12:07:37 UTC #1

I have been on a bit of an 8-bit bonanza on the Ulx3s ECP5 board and have now implemented the following retro computers and consoles: ZX Spectrum, Vic 20, TRS-80 Model 1 (and Video Genie), MSX 1, ColecoVision, Sega SG-1000, Cosmac Elf, ZX80 (only partly working), Gameboy (only slightly working), Acorn Atom, BBC Micro, CP/M, Jupiter Ace, Apple 1. The platform also has the Apple 2, Orao, Galaksija, NES, TI-99/4A, Ti-99/2 and Altair 8800.

If anyone is keen on having anyone of these or any other 8-bit computers (other than the ones already available), on the Blackice Mx or the Blackice II board, I can have a look at it. Porting to the ECP5 is easier as there is much more BRAM available and it can be dual-ported. On the Blackice boards more use of SRAM or SDRAM is needed.

On the ECP5, for most of these computers and consoles, games can be loaded from the SD card via an on-screen display (OSD). This would be harder on Blackice boards but may be possible with some firmware development.

bytter 2020-07-02 13:12:44 UTC #2

Wow, that's quite a list! I would love to have the MSX1 and Apple 2 working on this board, now that I've done my RGB444 dual PMOD VGA adapter

lawrie 2020-07-02 13:59:34 UTC #3

The Apple ][ implementation of the Ulx3s is in VHDL - https://github.com/emard/apple2fpga, and is currently built with Lattice tools, not the open source toolchain. I don't know if Yosys will now build it with the GHDL plugin - I haven't tried. Also, I am not at all familiar with the source code for this, so porting it to ice40 might be difficult.

MSX 1 has more of a chance, as it is in Verilog and I wrote the top level, and the video code. The top level uses some code from @hoglet's projects. https://github.com/lawrie/ulx3s_msx

I will look at how big a job it is to port this to Blackice boards. It is the Blackice Mx (with SDRAM) that you are interested in?

When MSX is ported, you get the ColecoVision and the Sega SG-1000 consoles practically for free, as they are very similar.

bytter 2020-07-02 14:54:05 UTC #4

Yep, Blackice MX here. If you start the project on GitHub, drop me a message; I will be more than willing to help/debug it out.

bytter 2020-07-02 14:56:49 UTC #5

BTW, noob question here, but AFAIK the HX4K doesn't have a DAC. What do you guys normally use to convert the usual 8bit DOut sound? PWM?

lawrie 2020-07-02 15:48:42 UTC #6

Yes either PWM or PDM (pulse density modulation). See for example - https://www.fpga4fun.com/PWM_DAC.html

The Ulx3s board has a 4-bit DAC. On that board, you can combine, the DAC output with PWM to increase the resolution.

lawrie 2020-07-02 16:01:03 UTC #7

Another article on PWM and PDM - https://zipcpu.com/dsp/2017/09/04/pwm-reinvention.html

PiotrS 2021-01-01 23:43:20 UTC #8

I'd love to run the Beeb on a Blackice MX

lawrie 2021-01-02 10:48:02 UTC #9

I have been slow getting round to porting any 8-bit computers to the Blackice Mx, as it is easier to port them to the Ulx3s. On that board, I have added a few more retro computers, including the QL and the Mac Plus (both 68000 machines), and i am currently working on the Sega Master System.

It is harder to get the Beeb working on the Blackice Mx, than the Acorn Atom, because of the way it uses RAM, but with changes that @hoglet made for other boards, I think it is now possible to use SDRAM on the Blackice Mx and get to HDMI working on the Ulx3s (where my port currently only supports VGA). Doing this is not very high on my priority list, but I might get round to it sometime.

On Blackice boards, I am currently more interesting in using nmigen and in using the n6800 nmigen implementation of the 6800 cpu. Variants of that (such as the 6809 or 6803) are used in computers such as the Tandy Coco, Dragon 32/64, Tandy/alice MC10, etc.

It is a pity that more people are not working on getting retro computers working on a variety of open source boards. @emard, the creator of the Ulx3s board nearly has the C64 working. That board has far more retro computer implementations working on it than any other open source board.

Of course the board with the most retro computer implementations by far is Mister, but that is not an open source board, and does not use the open source toolchain.

It is quite hard to convert Mister implementations to open source boards, as it uses a lot of VHDL, and its host processsor runs Linux and is much more powerful (and more tightly coupled to the FPGA) than the host processor on the Blackice boards. But with the Yosys GHDL plugin, it is becoming easier to convert Mister cores. @daveshah1 got the SNES core at least partially working on the Ulx3s board using GHDL, and @emard is doing the same for the C64. The Blackice boards are probably not powerful enough to run SNES, but a C64 implementation using SDRAM is probably possible.

Another computer I want to work on soon is the Amstrad CPC.

BigEd 2021-01-02 16:42:45 UTC #10

I'm guessing, @lawrie, you've seen Dave's changes for the Spectrum Next, which considerably simplified and improved the clocking? Dave did hope this would make it easier to support SDRAM.