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Commander X16

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Re: Commander X16

#111

Post by cmrdporcupine »

hth313 wrote: post #105
cmrdporcupine wrote: post #82

Earlier quoted context omitted.

Yeah the Mega65 is also going to have these oddities. From reading though it does sound like it offers a nifty 32-bit single register from merging A,X,Y,Z. And I believe it also has relocatable direct page. So some tricks borrowed from the 6809. When I was playing with the 816 I did use the technique you describe using the direct page. But I recall there being limits on where I could use that. The 816 is a bunch of c…

I looked at the Mega65 with its three (not quite) 6502 CPU variants and I just found it so weird. Basically no 16 bit operations, instead a couple of 32 bit operations. Z register is no longer 0 and you have to set it non-zero to change bank configuration. Five instructions (nine bytes) to change bank and I do not understand how you can save the previous bank setting in case you want to restore it. If you move the st…

To be clear, the value (to me) of the MEGA65 is not that its CPU is superior. It's that the developers of the project are spending a lot of time on the hard part: cases, keyboards, software, and tooling.

They have GEOS running on it, they have backwards compat with the C64, they have games modified to use its extra capabilities, they have injected molded plastic cases, they have keyboards and keycaps manufactured, they have a version of the Kernal and BASIC ported and expanded, they have a user manual, etc.

And it's a) open source and b) open.

And b) is key because they're also making it possible for their hardware to be used with other FPGA bitstreams, including ones developed for the MiST/MiSTer. They demoed their hardware being used with a GBA core running a GBA game.

Further, they seem to have a CC65 backend -- I don't know of what quality -- but it seems C based software is running on it.

That makes it an interesting and more complete platform and consumer product.

And if I want a better 6502 variant on it, I could do that myself and use one of the various 65xx variant cores out there, or write my own.

EDIT: And, yeah, from my perspective from just casually reading their docs is that the CPU in the MEGA65 is an 8-bit CPU with bank switching and a couple weird 32-bit ops. It's not a 16-bit machine despite.

But the thing about the 816 is that it's only _sort of_ a machine with a 24-bit address bus. It effectively just has a bank switching mechanism, but not external. Mensch really just bolted some stuff onto the front of the 65C02 and widened the accumulator and registers by 8 bits. But the 16-bit registers are a pain. I just wish he'd added some new registers (and a way of combining them) instead of having the mode switch.

Re: Commander X16

#112

Post by cmrdporcupine »

hakfoo wrote: post #107
wvenable wrote: post #87

Earlier quoted context omitted.

I'm building a hobby computer from scratch with a modern 80s era CPU. Anyone doing this kind of thing as a hobby has to decide what kind of project it is, what you want to get out of it, and where you draw the line between modern and old. For me, I had never done electronics before so actually wiring up the components and doing logic at a electrical level was interesting in itself. But also I'm interested applying my…

Why not a 65816? That gives you the 6502 compatibility and a larger address space mode when you want it. In a way, an anemic CPU makes sense if you go back to the old Commodore model of smart peripherlas. You don't need a lot of CPU horsepower, for example, if you can communicate with the mass storage/network card/etc at a high level and it just DMAs into place.

The bus de-multiplexing with the 65816 is a pain for amateur hobby stuff.

A W65C265S is worth looking at, tho it has some annoying masked ROM shipped on it you have to work around. It's basically an 65816 + UARTs + PIA + other stuff all packaged together. It has a boatload of pins which can be programmed to be either GPIO or the full address bus of the 65816 (instead of having demultiplex them like on the real 816).

Comes in PLCC format, which is relatively hobbyist friendly as you can get adapters for breadboard, and it can be done thru-hole. Only downsides I found are the onboard ROM (which you can shortcircuit around I believe) and its maximum bus speed is 8mhz, lower than the 14mhz of the 65816.

Re: Commander X16

#113

Post by TeaDude »

derefr wrote: post #104
karmakaze wrote: post #60

Earlier quoted context omitted.

This sounds like a much better spec. Using the 65c816 keeps the 8-bit vibe but doesn't force you to play the bank switching game to access more than 64K. DVI instead of VGA itself is also enough to give it a much better chance of success.

> Using the 65c816 keeps the 8-bit vibe Given that a 65c816 is what’s in the SNES, I’d say it has a distinctly 16-but vibe. Don’t get me wrong; 16-bit is my favorite! Far too few retro projects targeting early-90s era tech, or its portable early-2000s mirror. (Imagine if you will: a plug-and-play with extended GBA-clone hardware, with a tile-and-sprite PPU that could push 1080p@60 with tons of layered graphics colour…

Don't forget the hardware divider and the DS's sound capabilities!

I don't think retro 3D is a bad idea though. Just do what the DS does (keeping it separate from 2D in the process) and I think it would probably be the greatest console ever made.

Re: Commander X16

#114

Post by karmakaze »

hth313 wrote: post #81
cmrdporcupine wrote: post #74

Earlier quoted context omitted.

It's true you don't have to bank switch... but... the 816 doesn't have 32 bit or even 24-bit registers, so working with memory regions over 64k (such as the video framebuffer) is surprisingly awkward. You end up fiddling with the bank registers a lot, and doing a lot of futzing around. Having screen resolutions that require a framebuffer >64k isn't a good match for it, for example. And the program counter is a 16-bit…

You can work with 24 bit pseudo registers in the direct page using the [dd],y addressing mode, basically scaling up the very useful (dd),y on the 6502 to be 24+16 bits instead of 16+8. I am currently working on a compiler for the 65816 and has taken the approach of avoiding mode shifts as much as possible. I also lock the direct page and bank register to a fixed place while running normally. This simplifies it a lot.…

There was sort-of a 16-bit revolution--it wasn't connected to the 8-bit one. The 68k systems were 16-bit hardware with all new/different operating systems. It was much later we got 68020 32-bit hardware. The IBM PC/AT was 16-bit hardware following the 8-bit 8088 PC. That got us to DOS/16M and Windows/286 and OS/2 v1.3 (good times). On the fun side we got the 16-bit wave of consoles. It was all very semi-business though--I really missed the 8-bit days all through this period. The best times were probably on the Amiga in EU.

Re: Commander X16

#115

Post by derefr »

TeaDude wrote: post #113
derefr wrote: post #104

Earlier quoted context omitted.

> Using the 65c816 keeps the 8-bit vibe Given that a 65c816 is what’s in the SNES, I’d say it has a distinctly 16-but vibe. Don’t get me wrong; 16-bit is my favorite! Far too few retro projects targeting early-90s era tech, or its portable early-2000s mirror. (Imagine if you will: a plug-and-play with extended GBA-clone hardware, with a tile-and-sprite PPU that could push 1080p@60 with tons of layered graphics colour…

Don't forget the hardware divider and the DS's sound capabilities! I don't think retro 3D is a bad idea though. Just do what the DS does (keeping it separate from 2D in the process) and I think it would probably be the greatest console ever made.

It’s not that 3D is un-retro; it’s just a tempting crutch. Give people “free” 3D, even a little, and they’ll use it to the exclusion of interesting 2D effects. You’ll get FF7 instead of Terranigma / Symphony of the Night — still retro, but 1. the wrong era, and 2. not taking any advantage of the distinctive cool stuff the hardware can do, instead looking like every other low-poly 3D game.

Same with bitmap modes: people will use them as a crutch by combining them with software rendering.

(Maybe this could be fixed by putting a hard cap on the 3D frame rate. Maybe even make it so low that all 3D must be precomputed, baked down into a tile map and used through sprites! Under that restriction, it could look arbitrarily good, but the results would still look more SMRPG than Goldeneye.)

And same for sufficiently-good PCM sound. The ideal early-90s sound chip would be something like 128-voice polyphonic MIDI with a huge wavetable (but banked — no playing PCM by walking wavetable samples), passed through an arbitrary FM synth module, with the whole thing being bytecode that can do loops and branching.

Re: Commander X16

#116

Post by ibobev »

aniou wrote: post #13

Speaking of "modern retro computing" there is already a player in the town: C256 Foenix [1]. Based on 65c816, affordable, powerful and - most important - already available and well tested. It definitively deserve for user interest. For curious - there is an emulator available [2] (even one-and-half, because mine [3] is rather limited and created mostly for Forth [6, 7] development). 320x240 (double-pixel), 640x480, 8…

> Speaking of "modern retro computing" there is already a player in the town: C256 Foenix

Is there any community site where I can download software for this machine? It is a very good feature of the other retro projects that there are centralized websites where can be distributed and downloaded software. For ZX Spectrum Next[1], for Commander X16[2] and for Mega65[3].

[1] https://www.specnext.com/software-directory/

[2] https://www.commanderx16.com/forum/index.php?/files/

[3] https://files.mega65.org/html/main.php

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