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Commander X16

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Re: Commander X16

#81

Post by hth313 »

cmrdporcupine wrote: post #74
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.

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.

Segmenting your functions/code block on 64K is not a huge limitation. How big functions do you write? LOL

The 65816 does require more discipline when programming than the 6502.

Yes, they all went 68000 which is no wonder as it was a step up further. The 16 revolution never really happened, we went from 8 to 32 bits computers.

Commodore did go back to modify the 6502 later, that was the Commodore 65. That the C65 project went as far as it did is beyond me. I would have stopped it immediately if I was shown it at the time, both from marketing and technical aspects. Today, I suppose it makes some minor sense to revive it as a curiosity, just for the sake of it.

I wonder how you can find the 65816 odd, when the Mega 65 comes with three altered variants of the 6502. Also considering that some well known 6502 programming idioms no longer works as before, as soon as you move the zero page or the stack. Having studied them all, I find the 65816 puts those 6502 variants to shame.

Re: Commander X16

#82

Post by cmrdporcupine »

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.…

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 compromises. And some awkward ones because the opcode space was all eaten up.

Re: Commander X16

#84

Post by kwdc »

I think this is a good idea. If successful, it will create a stable platform for 8 bit 6502 people to target their creations and talk about as a community. Those involved are making compromises as time goes on as the ideas hit reality. From what I can see the compromises seem appropriate.

I can easily see a small island of activity around this platform. Plenty of scope for wikis, social media, youtube, etc etc.

Re: Commander X16

#85

Post by rzzzt »

codeflo wrote: post #17

Something I’d buy, and that the Raspberry Pi almost might have been, is a computer running a “retro OS” (instantly boots, BASIC-like commands, direct access to hardware) on a semi-modern ARM chip with a few megs of RAM and HDMI out. That would be fun to tinker with and program for. The problem with this is that it’s so incredibly hard to do anything in 8-bit, I can’t imagine many people going to all that trouble if t…

You could boot BMC64 on the Pi: https://github.com/randyrossi/bmc64

Re: Commander X16

#86

Post by rzzzt »

yc-kraln wrote: post #16

I think the lack of USB, as irritating as it is to implement, relegates this to the "curiousity" bin--not for keyboards, per se, but for storage and other connectivity. Still a cool project, though.

There is an SD card slot on it that you can use for storage.

Re: Commander X16

#87

Post by wvenable »

cmrdporcupine wrote: post #49

All these machines end up involving one or more FPGAs -- to varying degrees -- simply because of the requirements and logistics. There's varying types of purism involved ("FPGA only where we would have used a custom chip" or "FPGA but not for the CPU" etc) but once you start down that path the whole thing starts to seem silly as with many of these machines the entire functionality could be done on a single relatively…

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 programming knowledge to the limitations of that era. It's sort of an art project. No matter what, a computer today with an 8Bit CPU isn't practical.

I'm going to have a 6502 CPU, I'm going to try for 1MB of RAM banked, SD card for storage, and I'm thinking of using a Pi Pico as a VGA graphics card. Obviously using a Pi Pico in a project with an 8bit CPU is "silly" but that still satisfies my own goal. Other people working on these types of computers tracking down chips from that era or are building their own TTL-logic basic graphics cards because they have different goals.

Re: Commander X16

#88

Post by wvenable »

mattowen_uk wrote: post #38

When David Murray (8-bit-guy) first announced his 'dream computer' I was quite excited. His early descriptions were akin to something like a C128 but with more colours, faster CPU and modern connections, all in a single case, like the C128(not D) or C64. Plug into a screen or TV and just 'go'. Somewhere along the way serious scope-creep happened, and now we've got something that looks and feels just like a mini-ITX D…

The outside might not give you retro-vibes due due the case/keyboard design but inside it's still pretty retro. It's running an 8bit CPU and Microsoft BASIC.

Nothing is stopping you from buying the board and 3D printing a retro case/keyboard for it.

Re: Commander X16

#89

Post by wvenable »

billpg wrote: post #76

I don't get it. I get building a C64 (or other retro systems) but with HDMI ports and components that can be sourced without dumpster diving. I don't want to replace a bunch of capacitors to play 80s games either. But why would I spend good money on a Commander X16 when I could buy a (say) Raspberry Pi. If I'm going to buy a modern system, then why not buy a modern system?

But it's not a modern system. At it's core is an 8Bit CPU.

Re: Commander X16

#90

Post by chalcolithic »

selfhoster11 wrote: post #27
chalcolithic wrote: post #18

While I love, love, love retrocomputing I don't understand why 99% of it is "retro-next" computing - instead of designing computer from some era people like to design much beefier next-gen machines. 2MB of RAM? 640x480? Why not use Amiga instead? Designing a machine that would beat c64 is insanely appealing to me. Designing a machine that would beat c64 because it came out a decade later and had larger ram chips and…

At a guess, it's harder to get your hands on weaker chips in larger quantities. Larger chips are dirt-cheap, while for weaker ones you'd either have to raid NOS from warehouses, or fab it yourself (which is expensive, and sometimes outright impossible - I don't think we've got the tech to fab a SID chip any more, for instance).

That is totally understandable, but do they have to use the whole chip?
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