Posted By
Frederick
on 2019-02-04
22:17:05
|  Re: Possible Plus4 successor
@Claude, I think I'd be interested in something like this depending on the final nature of the product and the price it comes in at. I'm less interested in a "better" Plus/4 and more of a truly Plus/4 compatible built using modern hardware, even if internally it's just a high-quality emulation. I'd also be more interested if there were a standard way of using it in its original configuration, i.e. as a computer in a case with a keyboard. Also, a few other thoughts:
If you're thinking of using a DSP for this, have you looked into essentially building a carrier board for an existing off-the-shelf system of the regular ARM variety? Note that The C64 Mini basically ran Vice on an Allwinner ARM SoC and apparently does quite well in terms of emulation performance. I should think we could take YAPE or Plus4emu and do the same on similar hardware. In particular, I might suggest either the Raspberry Pi Compute Module or one of the TI OMAP processors as used in the Beaglebone Black.
The first thing that comes to my mind would be a Raspberry Pi of course (and the Pi1541 seems to prove that you can bit-bang a lot of the IO functionality necessary using GPIO pins, but I also think you'd run out of IO pins if you're going to handle all the different machine ports). There's also the Raspberry Pi Compute Module but you'd have to design your own carrier board for that, I believe.
I might also suggest looking at some of the cheaper Beaglebone boards as they have a large number of GPIOs along with HDMI output, in particular the Beaglebone Black might be something worth looking into at prices of $60 USD per part. If memory serves, the ARM processor from TI used on the various Beagleboards has a programmable real-time unit (PRU) that might be exactly what you're wanting for something like this. There may also be OEM modules that are essentially the same circuitry on a SoM package but it's been a while since I looked into that.
You could also look at the Propeller 2 as it's essentially trying to be somewhere in the "programmable hardware" category, but it's very early in its release cycle at this time. It's a lot more powerful than its predecessor and could probably be a minimalist solution for you, but you'd be getting into some relatively obscure hardware. That said, it might be worth checking out as well. I have a soft spot for the Propeller family of devices as several years ago it was used in a lot of old-school emulations of systems like the ZX Spectrum, and I've found the current Propeller to be a suitable programmable replacement for the equivalent of a low-powered FPGA in retrocomputing projects.
(Disclaimer: I'm also a bit of an electronics hobbyist and briefly sketched out some ideas on how to reimplement a Plus/4 using a 6502 and Propeller 1, but finally gave up on the notion as I don't think the fidelity of the emulation would be nearly accurate enough for the best games, and the Propeller 1's native NTSC and PAL generation doesn't match up well with the TED color palette either. In the end I still ended up working on a 6502-based retrocomputer but gave up on the notion of Plus/4 compatibility rather early on.)
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