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