RPi Pico As A Sinclair ZX Spectrum 128K +3

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[@j_bizzel]

Excellent video and excellent development. Thanks for this awesomeness!

[@DevelopIT]

Thank you.

[@syrus3k]

What is this sorcery?! Amazing

[@rootbeer666]

Wait, you're driving VGA with this, which is 60Hz+, depending on the mode. Since Spectrum was not popular (mostly non-existent) in the NTSC regions, most programs you will find are for PAL 50Hz output, meaning the timing will never be right on the 60Hz+ output.

[@DevelopIT]

The ULA in the Spectrum uses DMA to access the memory and display the image. As this is an emulation, it can go into the memory and get the information at any time it wants to.

[@fastbeta]

I made my own ZX Spectrum 128 computer with Beta Disk Interface and VGA output (precise timings) on a RP2040 microcontroller board. Feel free to ask any questions

[@TooSlowTube]

@@fastbeta Is your Spectrum emulator open source? I see there are videos about it on your channel, but there's no context given. I guess those are on a web page somewhere, illustrating it, but seen here on YT, they're a bit of a puzzle. As the last commenter there said... ?? It would be good if you filled in the video descriptions with some hardware details and a link to anything relevant, like a repo or a project page. I'm interested but there's not much to go on, so far.

[@fastbeta]

@@TooSlowTube hi. i have links (telegram groups) in the description of my YT channel. i can answer there. also i can answer on polish speccy pl forum

[@TooSlowTube]

@@fastbeta Thanks. I would not have guessed, even if I'd looked at your channel About page, which I didn't :) I'm not familiar with Telegram. Are the links supposed to work in a web browser? It's not working for me, so far.

[@JulioAndujar]

Any more details in this project? I think is super cool

[@DevelopIT]

I will be getting back to it. I allowed myself to get distracted by a ColecoVision project currently.

[@lumsdot]

Does AY sound work?

[@DevelopIT]

It works on the emulator under Linux. When I get back to the Pico I may have to start looking at assembly code for some features to get the performance. I haven't tried it yet.

[@arnolduk123]

Where are your project pages for these pico emulators ?

[@DevelopIT]

I am hoping to ultimately make PCBs to sell. And the project will run all the emulators I am currently working on with a VT100 terminal built in too. Don't know how long it will take though.

[@presechmax]

А в чём проблема подключить микросхему SPI SRAM?

[@DevelopIT]

Это хороший момент. Я не пробовал и не знаю, как это сделать. А поскольку флэш-память SPI, то это должно быть возможно?

[@b213videoz]

can it read floppy discs ?

[@DevelopIT]

Not yet. It's something I may get back to later.

[@SianaGearz]

Why 77K video? You only need a few lines worth of video output data buffer (circular buffer) that you just generate from Spectrum's video memory image in RAM, no? A few lines at a time, no need to keep the whole frame.

[@DevelopIT]

I'm using DMA to send the whole video frame to the display. So I can use the CPU for emulation without having to handle video output. Which means I can write the emulator code completely in C and not have to go to assembly for speed. The code is easier to move between different systems when it is just C.

[@SianaGearz]

@@DevelopIT You can have an interrupt routine refill the circular buffer every few lines with data to be DMAd, can't you. The rest of the emulator can stay as is.

[@SianaGearz]

I wonder if you can DMA a shuffled version of Spectrum VRAM in display order (with attribute byte interleaved) into the PIO which then generates output signal.

[@DevelopIT]

@@SianaGearz The CPU would then have to take time to service an interrupt the number of segments your suggesting times 50 per second. And at each interrupt decide which lines to render, render them and start the DMA. This also has to happen within one hsync period. Where as I am performing one operation 50 time a second, and that is to render the frame then restart the same DMA as last time. And it can occur any time in the larger hsync period. Which allows me to use C code with no assembly code.

[@nonoyorbusness]

You're a brilliant guy, but your presentation is very difficult to follow, however that's not minimising your achievement which is great.

[@DevelopIT]

I'll see what I can do. I try to keep the length of the videos down so not be too demanding on peoples time.

[@syrus3k]

I thought this was fine.. but then I'm into comp sci, zx spectrums and coding..