New Acorn 8bit? Should there be one?

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jms2
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Re: New Acorn 8bit? Should there be one?

Postby jms2 » Mon Feb 06, 2017 9:28 pm

BigEd wrote:As a calibration, here are some of the features of the Spectrum Next, which might help us understand why it exists:
- nice new plastic case


What I like about the Spectrum project is that (irrespective of whether or not it's a good idea overall) it undeniably has creative merit. Not only is the hardware custom made, the case is a really nice piece of design - not just new in the sense of being newly made, but new in design terms as well.

Just for fun, this has set me wondering what an equivalent new Acorn 8 bit machine might physically look like... it's not easy because we already have quite a lot of design variety even if you exclude later machines such as the A3000 etc. And the red function keys were very much a BBC (rather than Acorn) feature. So on reflection I reckon a modern Acorn machine should look quite a lot like an Atom, only a bit bigger, with a Master style keyboard - combined with the indefinable (to me anyway) glossy newness that the Spectrum Next has. Although it's tricky to envisage a combination of newness and chocolate brown!

Any industrial designers on the forum?

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Re: New Acorn 8bit? Should there be one?

Postby dgrubb » Mon Feb 06, 2017 9:44 pm

It's a lovely looking piece of kit, which is where a lot of the draw is. What I would pay good money for is an Archimedes-style inspired case, with modern outputs (USB, Ethernet, HDMI etc), into which you could just slot a Raspberry Pi Compute module loaded with the current RISC OS version.

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Re: New Acorn 8bit? Should there be one?

Postby paulv » Mon Feb 06, 2017 9:50 pm

dgrubb wrote:It's a lovely looking piece of kit, which is where a lot of the draw is. What I would pay good money for is an Archimedes-style inspired case, with modern outputs (USB, Ethernet, HDMI etc), into which you could just slot a Raspberry Pi Compute module loaded with the current RISC OS version.


Like this?

http://blog.tynemouthsoftware.co.uk/2016/04/acorn-a3000-usb-keyboard.html

Paul

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Re: New Acorn 8bit? Should there be one?

Postby BigEd » Mon Feb 06, 2017 9:53 pm

It takes very little to fire my beeb-loving neurons. The Beeb-coloured option for the Pi Fuze case is an example:
Image

Now, this is built down to a price. The metal case is fairly basic as a material, the keys are soft low profile type, and the angle is all wrong. But I wonder: how good does a keyboard have to be to meet people's expectations? Must it be full-travel key switches like the Beeb and Master?

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Re: New Acorn 8bit? Should there be one?

Postby BigEd » Mon Feb 06, 2017 9:58 pm



The work Dave does is great, reusing the cases from dead machines. I expect this is the best approach. There are enough for all of today's enthusiasts but I don't know if there are enough to inspire a new generation of bedroom coders.

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Re: New Acorn 8bit? Should there be one?

Postby lazarusr » Mon Feb 06, 2017 10:34 pm

I think it is important to fully understand the market for the Spectrum Next and similar. We have been looking at this from our own perspective and I do not think anyone who has contributed to the thread is representative of the target audience.

The ZX Spectrum sold in the millions. Most of the owners were probably kids who may have dabbled in code and got as far as putting the following on the demo machine in WH Smith:

Code: Select all

10 PRINT "NATALIE GREEN IS SMELLY"
20 GOTO 10

Before using it for what they really wanted – playing games. Then they grew up, lost or binned the Speccy and led lives that, unlike a lot of the hard core enthusiasts on here, had very little to do with computers and electronics.

Now they are in their 40s and having a bit of nostalgia for the games they played as a kid; maybe they want to show their kids what 'proper' games were like. However, these are not the kind of people who are likely to buy 30 year old secondhand electronics from eBay let alone repair or tinker with them. Equally, they are unlikely to want to install and configure emulators. Remember, there are a lot of people out there who do not feel comfortable installing anything on a PC - they just want to use the stock apps it came with. Increasingly, there are families where the only digital device is a phone or tablet.

What they want is something they can buy, that works out of the box and is fully guaranteed. This is what was behind the success of the Spectrum Vega - something which for me, and probably many others on here, is the very antithesis of what is attractive about 8-bit computers.

Which brings us back to the who would buy such a thing based on Acorn computers. There is unlikely to be a market for people who have a nostalgia for the school computer labs and the people who had Beebs at home are likely to include a much large cohort of teccy types like us who would want to tinker with vintage electronics. The real market would have to be former Electron owners - and that is a much smaller group than former Speccy owners.

Oh, and one final thing, Natalie Green was smelly.

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Re: New Acorn 8bit? Should there be one?

Postby lazarusr » Mon Feb 06, 2017 10:40 pm

BTW, in terms of a design for a new Acorn case - I think a move away from the Utilitarian design of the 80s machines is required. It would need to be thin and sleek (much like the Spectrum Next). It MUST have red function keys. But I do not think it should have the full classic 80s cream. It would need to be brought very much into the new millennium. I would suggest a black case (or possibly white if you are Apple inclined) with cream keys and accents.

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Re: New Acorn 8bit? Should there be one?

Postby flynnjs » Mon Feb 06, 2017 11:38 pm

BigEd wrote:As a calibration, here are some of the features of the Spectrum Next, which might help us understand why it exists:


Maybe we should hack these to give them an Acorn personality too :twisted:

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Re: New Acorn 8bit? Should there be one?

Postby 1024MAK » Tue Feb 07, 2017 12:34 am

Well, I think people should be careful when they start pigeon holing.

Will the market for a new Acorn 8 bit be smaller than the Spectrum Next? Likely yes. But if you talk it down, that does not help... [-X

Different people want different things, and the fact that prices on eBay for retro computers generally are rising indicates that there are a lot of people who want working Acorns (mainly BBC B machines). That is part of the possible market for a new machine, not just the regulars on this forum.

Also, you never know, there may be loads of people who loved using BBC B's and Master 128's at school, but back then the cost prevented them ever getting one, nostalgia may well play a part still even for these people.

There were similar comments on the World of Spectrum forums about the Vega and the Vega+. Not quite the same, I grant you, but who would have thought that an 8 bit games machine would have done so well in this age where the mobile "smart" 'phone is also a gaming machine :!:

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Re: New Acorn 8bit? Should there be one?

Postby paulb » Tue Feb 07, 2017 1:06 pm

jms2 wrote:So on reflection I reckon a modern Acorn machine should look quite a lot like an Atom, only a bit bigger, with a Master style keyboard - combined with the indefinable (to me anyway) glossy newness that the Spectrum Next has.


I always liked the look of the Atom, although the ridges must make the case very awkward to dust off. Maybe the Master Compact (keyboard) would be a reasonable starting point, but without the whole "black cardboard" keyboard inlay, going with the uniform moulding of the Electron's keyboard instead (whose grid plus logo decoration I always liked, and is very retro, so might actually be a better inspiration). This Spectrum Next thing might be nicely contoured and looks very shiny, but like the Spectrum+ it presumably follows on from, it still looks like a toy. (I see that they have to point out that the keyboard is not the same.)

dgrubb wrote:What I would pay good money for is an Archimedes-style inspired case, with modern outputs (USB, Ethernet, HDMI etc), into which you could just slot a Raspberry Pi Compute module loaded with the current RISC OS version.


I'm not a big fan of retro repackaging of modern machines, even though RISC OS really would run on the actual hardware in that case. No thanks to that RPi Compute Module, though: it just seems like a very awkward way of putting that hardware in stuff - maybe Broadcom got too good a deal on memory connectors and has to dump them into the market as well - and although anyone using the RPi is unlikely to be bothered by the single-sourcing issue, I'd rather see more open standards for computing modules being used. That said, given the "if you have to ask, you can't afford it" pricing of the RPi Compute Module I/O board, what you suggest could indeed be lucrative.

BigEd wrote:The Beeb-coloured option for the Pi Fuze case is an example


This is the kind of thing that is obviously "just a bit of fun", but it is at the same time also an indictment of the "pretend culture" (I could say "hipster culture") that passes for normal these days. You're right that it was built to price, and I wonder what the margins were for what an unkind person might call a shoddy repackaging of the contents of a bargain bin.

lazarusr wrote:The real market would have to be former Electron owners - and that is a much smaller group than former Speccy owners.


I'm not sure it is limited to that. Some people like to pretend that they liked the Beeb or don't actually hate it - the vocal hate brigade are, of course, not necessarily representative - and you can see this with the Raspberry Pi and the way it was pitched. But as I was speculating about the case (above), I started to think that if one wanted to emphasise "retro", the Electron would be a better starting point: it may be the last Acorn product whose physical characteristics were entirely custom designed or chosen for the purpose; you just need to look at the 8-bit successors to see re-use of the Electron or Beeb parts; the 32-bit products were all increasingly incorporating generic elements.

1024MAK wrote:Different people want different things, and the fact that prices on eBay for retro computers generally are rising indicates that there are a lot of people who want working Acorns (mainly BBC B machines). That is part of the possible market for a new machine, not just the regulars on this forum.


I think that the demand for retro computers exceeds supply, and acquiring machines from eBay isn't really a sustainable or efficient activity, either. Plus you need to have knowledge about them to avoid hazards - Beeb capacitor problems and general component aging - and to actually use them with modern displays and storage. So, while I personally think that it's great to sustain and enhance the actual old machines, I think there's absolutely a demand for newer machines that seek to reproduce the experience.

As I've now said far too often, what interests me more than fantasy remakes is the extrapolation of the old machines in a different direction to that pursued by their manufacturers, which is something that can be done with modern technology in a historically sensitive way, while also delivering a modern, reliable, and hopefully longer-lived product. That last part may be the most important part of all.

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Re: New Acorn 8bit? Should there be one?

Postby RobC » Tue Feb 07, 2017 9:52 pm

1024MAK wrote:Will the market for a new Acorn 8 bit be smaller than the Spectrum Next? Likely yes. But if you talk it down, that does not help... [-X

To be fair, the thread asks whether there should be a new Acorn 8-bit machine so I think that it's reasonable to give honest opinions about the potential market for such a machine.

1024MAK wrote:Also, you never know, there may be loads of people who loved using BBC B's and Master 128's at school, but back then the cost prevented them ever getting one, nostalgia may well play a part still even for these people.

That wasn't my experience as a Beeb-owning kid in the 80s. The vast majority of my classmates thought that their Speccys and C64s were superior as they had better/more games. Yes, a few (more discerning/enlightened individuals!) appreciated the Beeb's superior BASIC and expansion possibilities but I can't say that many were envious of me (with the possible exception of playing Elite when it first came out).

I can see the point of having new hardware to avoid having to constantly repair machines and search for obsolete components but the MIST FPGA board caters for that and has a much bigger potential market than a Beeb-specific machine. (Actually, a MIST FPGA board and one of Sprow's red function key USB keyboards wouldn't be bad as a modern Beeb/Arc :idea: :D. )

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Re: New Acorn 8bit? Should there be one?

Postby JonC » Tue Feb 07, 2017 10:22 pm

Should there be one, well in my view yes...

I agree that we could build it on an FPGA (Atom/Elk/B/Master etc) and attach the right I/O to connect, not only to newer hardware, but at least as importantly, to older hardware.
Keep the old ports that people know so they can still develop hardware and software projects and keep the hardware they have and use already. This is what the beeb was all about in my view expandability and adaptability.

Case-wise; the same general design is important, I think a newr robust keyboard would be best although I don't know how many old keyboards are left. I new robust keyboard would prevent the machine from being limited by old keyboard availability.

Ports: All the old ports should be under the case as currently layed out (possibly with a bit more clearance between them and better cable routing recesses). The back of the machine is the place to put the new ports, the majority of which (HDMI, USB etc) are small so there should be room to fit them.

This is of course, all my own opinion. Yes it will undoubtedly push the price up, but it will make it more accessible for everyone from the guys on the forums who still tinker with the originals, to the guys prowling ebay wanting to relive the 80's on modern screens/tv's for the minimum amount of hassle.

You could potentially have two internal i/o board instead (retro i/o and modern i/o) if combining the two proves too expensive.

Phew... and breath. Ok I'll shut up now! :mrgreen:
Jon
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Re: New Acorn 8bit? Should there be one?

Postby pixelblip » Mon Feb 13, 2017 9:33 am

One thing I like about the BBC is you switch it on and go.....like all old computers....no waiting around. To me hearing that beep and having it come on were the good old days (of course that wasn't just the Beeb)
I've been thinking of this (new Beeb) for a while now.........it's a good idea.

The colours of the keys should remain the same eh! They are so distinctive. How about a backlit keyboard. Are those difficult to do?

Do you think it would be a good idea to put a small tft screen into the unit ( that folds at an angle) ? That might sound like overkill ....but it means it could be an all in one unit you could take anywhere. Like a really durable laptop but with a smaller screen.

It would be good if it featured the original ports....(at least the 1mhz expansion port). Plug in your old AMX mouse :)

This could be so exciting. I might try a design.......that would be a thing, to win a design competition for a new BBC micro.....what an award that would be ...

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Re: New Acorn 8bit? Should there be one?

Postby daveejhitchins » Mon Feb 13, 2017 10:01 am

pixelblip wrote:Do you think it would be a good idea to put a small tft screen into the unit ( that folds at an angle) ? That might sound like overkill ....but it means it could be an all in one unit you could take anywhere. Like a really durable laptop but with a smaller screen.
This could be an option!

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Re: New Acorn 8bit? Should there be one?

Postby Bitstik » Mon Feb 13, 2017 2:08 pm

Hmm this has really got my interest.

IMHO one of the vital things will be a quality keyboard. That will add cost to it so I wonder whether, as a starting point, a quantity of ordinary Cherry USB keyboards could be ordered with red function keys? This, of itself, might help the BBC community if a new keyboard could be "adapted" to work with an old BBC.

That would then allow freedom in design of the case for the machine without having to worry about keyboard ergonomics (something Spectrum never concerned themselves with I believe :twisted: .

Whatever processor is in it I think it should have a tube interface with the same flexibility as the original- allowing processor developments in 30 years to be plugged in but for the moment a space for an internal rpi3 should be made available- perhaps, as with the Spectrum Next, the access to usb ports/hdmi on the pi being made available in the case. The keyboard might even clip into the front of the case for "old-skool" ( as I believe the yoof might say) feel.

The resulting machine could look like a Master Compact/ Viglen-cased BBC perhaps but sleeker.

PORTS:
USER, 1 MHZ bus (with internal connector as well), Disc-drive,TUBE, Printer, Econet, Analogue, HDMI, DIGITAL IN/OUT, HDSD card slot (or use the one on the Rpi? with, perhaps, a number of usb slots on the back to allow inexpensive connection of USB hardware (cheap FDD drives perhaps??), stereo output

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Re: New Acorn 8bit? Should there be one?

Postby dhg2 » Mon Feb 13, 2017 6:37 pm

This is a cool idea.

I was actually thinking of something like this before this thread was posted - I was thinking about how the BBC Micro has been (for me at least) a really good environment for learning about programming, about how computers work, and stuff. Then I thought it was a shame that to get that experience today, you have to buy (and then repair) expensive antique hardware from ebay.

If something like this were made, I'd definitely buy one. And I might also buy another one for my nephew. But at the same time, I can see that the market for this would be pretty small.
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Re: New Acorn 8bit? Should there be one?

Postby pixelblip » Mon Feb 13, 2017 8:26 pm

This render has been produced with the latest state of the art graphics cad software which features real time HDR rendering and realistic volumetric particle algorithms. It was piped to a render farm in Arizona and this mock up was sent back. As you can see from the detail and excellent rendering we have a good idea of what it might now look like. :lol:

There are 5 USB3 ports to the left of the laser etched backlit keyboard for you to plug in usb sticks that act like Roms (ready for the all new 2017 AMX Super Art USB rom that features a brand new Mode 2 palette :lol: ).......also health status led indicators on the right of the keyboard that indicate e.g if you have been playing Frak on the Beeb for more than 2 hours (which has been reported as being detrimental to some users' health in certain circumstances)

The lights also pulse and play in time with the latest incorporated Music 10,000 3d sound chip - it also features the latest state of the art stereo speakers (the large computer case acts as a subwoofer) and a rotatable TFT screen that might possibly feature the latest state of the art OLED Microvitec Cub 2017 panel if we choose to increase our kickfunding goal.

This model ( of a series ) is known as the BBC B squared 2017 and hopefully will be finished before the Bladerunner 2049 release in the summer of 2017 ( else a logo redesign is needed)

We are hoping it won't cost as much as a peak time Bladerunner 2049 3d Imax Saturday night ticket but we can't guarantee at this stage :lol: :D
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Re: New Acorn 8bit? Should there be one?

Postby pixelblip » Thu Feb 23, 2017 12:13 am

BBC Squared
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Re: New Acorn 8bit? Should there be one?

Postby leenew » Thu Feb 23, 2017 8:32 am

He he he... I'd buy it :lol:
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Re: New Acorn 8bit? Should there be one?

Postby finisterre » Mon Feb 27, 2017 1:02 am

I never owned a Spectrum, although I played on those of friends. My path was ZX81, BBC B, Amiga 500. But even I'm excited about the the Spectrum Next and will be backing it when it finally gets on to Kickstarter. I'd do the same for a modern Beeb, but it'd definitely have to look the part.

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Re: New Acorn 8bit? Should there be one?

Postby fwibbler » Wed Mar 01, 2017 7:52 pm

Personally I think the more powerfull you make the machine, the more people you are likely to need to get the most out of it and pretty soon you find you need a whole team of people to produce one game.
Perhaps a better idea would be to build the sort of machine that the Acorn Electron /should/ have been.
Of course, even on that, opinions differ.
My idea for that would be to have a machine using the same graphics and sound chips as the beeb for best backwards compatability.
Extra RAM would be good, but again, I suspect opinion will be divided on how much it should have. Lets face it, I dont think any games used /all/ the available RAM on a BBC Master so fitting more than 128K seems pointless.
Seeing some of the games made in the 8 or 9K left to a beeb in mode 1 or 2 suggests that a 64K machine would have been a games programmers dream, giving about 40K for programming in a similar Mode.
Finally, for a CPU, if a 6502 processor could be made to run at 4mhz (with an option to run it in a slow 2mhz mode for Beeb compatability) then you'd have a pretty powerful machine (by 80s standards) and one which the stereotypical bedroom coder could happily use by himself, rather than needing a team of people.

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Re: New Acorn 8bit? Should there be one?

Postby pstnotpd » Wed Mar 01, 2017 9:06 pm

Coming back to the fold I've been thinking about this as well.

We now have working and evolving emulations.

We could explore the idea of a 65815 as core processor, backwards compatible to the original acorn machines but with improved graphics, sound and perhaps internet connectivity (Sprow's ethernet board)

Just as a brainfart.... mode 0 in 256 colors, a screen mode which faithfully represents the original software graphics mapping, M5000 as standard sound, SID optional.....

As the PI copro seems to take off it can be incorporated, preferable over USB.

Try it out in emulation and if it works in silicon?

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Re: New Acorn 8bit? Should there be one?

Postby fwibbler » Fri Mar 31, 2017 5:41 am

I'm sure that such a machine would be capable of some great looking and sounding games, but you'd still need a team of people to make just one game.
You'd need a dedicated graphics artist for the graphics, a dedicated composer for the music and sound effects and a wizard programmer to tie it together and maybe even another person to oversee the whole project. And all this for a game that would have a very limited audience and never make any kind of profit.

Reading the posts from programmers here who are making (or have recently made) games for the BBC or Electron, it seems that the major limitations for them are a lack of RAM and sometimes also CPU power.

So as I said a few posts back, simply doubling the RAM and CPU speed should make the machine much less restricting to program for and could potentially retain the maximum possible backwards compatability with old software.

I admit that Mode 1 with 8 colours instead of just 4 would be nice, but even that might be possible with 64k RAM to play with and still allow for a larger program than the existing machines do.

It would be interesting to get the views of the current programers about this...

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Re: New Acorn 8bit? Should there be one?

Postby tricky » Fri Mar 31, 2017 7:40 am

For me, the audience is quite small as it is and making it beeb like is probably only going to appeal to a subset of beeb people, so a suit of cheap, easy to fit, backwards compatible add-on would seem to be a better option.

The recent work on an updated ULA is a great example of the sort of thing that is useful already without having to have code written especially for it; just changing the palette before running a game. With the hardware scrolling and blanking, it would make a whole genre of games easier to write for the beeb. The price is probably going to gate adoption and that is a shame.

I would have liked a shadow RAM type option to map the OS ROM as RAM, copy the ROM to RAM and then switch, apart from the memory mapped hardware, it would give even more memory available at one time and make OS upgrades a boot time option.

As I've mentioned before for games, I would like an option to make the screen layout sequential going down the screen in columns, if this were added as an option, it would make most games easier to write and faster to draw.

A blitter or even just a blit instruction in the CPU would be great too. blit src dst bytes would be a 6 byte instruction, having the option to COPY, OR, AND, NAND and even MASK, with either an extra src or interleaved with the src data would be great. This would allow the game to fill in a sequence of these while it was doing game logic and then fire them off during precious v-blank time or timed for when parts of the screen wouldn't be updating.

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Re: New Acorn 8bit? Should there be one?

Postby davidb » Fri Mar 31, 2017 10:33 am

tricky wrote:As I've mentioned before for games, I would like an option to make the screen layout sequential going down the screen in columns, if this were added as an option, it would make most games easier to write and faster to draw.

This would be nice. Just a couple of new modes like this would make things interesting.

tricky wrote:A blitter or even just a blit instruction in the CPU would be great too. blit src dst bytes would be a 6 byte instruction, having the option to COPY, OR, AND, NAND and even MASK, with either an extra src or interleaved with the src data would be great. This would allow the game to fill in a sequence of these while it was doing game logic and then fire them off during precious v-blank time or timed for when parts of the screen wouldn't be updating.

Your suggestion reminded me of an article about a machine that extends the 65C02 with new instructions. From the introduction:
It's a microcomputer that uses a 65C02 cpu teamed up with a coprocessor — ie; microcoded logic capable of interpreting the instruction stream in tandem with the cpu. To the programmer they appear seamlessly as a super-65C02, a new branch on the 65xx tree.

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Re: New Acorn 8bit? Should there be one?

Postby tricky » Fri Mar 31, 2017 11:52 am

I think the arcade game missile command had a mod that made sta (zp,x) write to a different ram than the others, which i believe it did by counting cycles to the write and swapping on the 6 th cycle of there was one.

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Re: New Acorn 8bit? Should there be one?

Postby davidb » Fri Mar 31, 2017 1:29 pm

fwibbler wrote:Reading the posts from programmers here who are making (or have recently made) games for the BBC or Electron, it seems that the major limitations for them are a lack of RAM and sometimes also CPU power.

The main limitation is lack of time - or the lack of time that can be justifiably used for making new games. :)

fwibbler wrote:So as I said a few posts back, simply doubling the RAM and CPU speed should make the machine much less restricting to program for and could potentially retain the maximum possible backwards compatability with old software.

I admit that Mode 1 with 8 colours instead of just 4 would be nice, but even that might be possible with 64k RAM to play with and still allow for a larger program than the existing machines do.

More RAM would be nice, though I think what we have might be enough if we are prepared to put code in ROM or swap out static data and/or code to disk. Perhaps having RAM mapped into the top 32K would be interesting. Having access to 16 colours, maybe choosing them from a wider palette, would also be nice.

Electron fans would also like decent sound capabilities. Perhaps Beeb users would be tempted by dual SN76489 (or other similarly retro) sound chips.

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Re: New Acorn 8bit? Should there be one?

Postby 1024MAK » Fri Mar 31, 2017 2:24 pm

tricky wrote:The recent work on an updated ULA is a great example of the sort of thing that is useful already without having to have code written especially for it; just changing the palette before running a game. With the hardware scrolling and blanking, it would make a whole genre of games easier to write for the beeb. The price is probably going to gate adoption and that is a shame.
The key things here are that the upgrade needs to be an easy thing for non-hardware people to do (so, remove chip, plug-in replacement chip or module); it needs to be reasonably priced; and a "killer app" as in "must have game" (better still, in addition a number of really good games) will be needed to encourage people to buy the hardware. Once the community starts talking about it, word will bring in more users, and hopefully in turn, more games will be written for it. It will however take a while. In the ZX81 community, a easy to use SD card storage & 32k RAM device (ZXpand) is now so popular, the creator has a job keeping up with demand.
tricky wrote:I would have liked a shadow RAM type option to map the OS ROM as RAM, copy the ROM to RAM and then switch, apart from the memory mapped hardware, it would give even more memory available at one time and make OS upgrades a boot time option.
Off the top of my head, I can't see a reason why a plug-in module can't do this. It will require a R/W line and a reset line to be picked up though.
tricky wrote:As I've mentioned before for games, I would like an option to make the screen layout sequential going down the screen in columns, if this were added as an option, it would make most games easier to write and faster to draw.
This requires changing the mapping of the video systems address lines to the RAM. So the 6845 CRTC would need to be replaced.
tricky wrote:A blitter or even just a blit instruction in the CPU would be great too. blit src dst bytes would be a 6 byte instruction, having the option to COPY, OR, AND, NAND and even MASK, with either an extra src or interleaved with the src data would be great. This would allow the game to fill in a sequence of these while it was doing game logic and then fire them off during precious v-blank time or timed for when parts of the screen wouldn't be updating.
So a replacement module in place of the CPU. Again doable. To be honest, this idea of a CPU having block move/copy instructions is not new (the Z80 has some: LDDR, LDIR), the trouble is, no one thought about or wanted to develop a more expensive 8 bit CPU where the CPU did not need to keep re-reading the block move instruction from main memory :-( [the Z80 does M1 instruction fetch cycles as shown by the refresh register (R) incrementing each time it increments/decrements the counter register and compares to see if the count is finished, if not finished, it jumps back to the block move instruction, reads it again and continues {"The R register is a counter that is updated during every Z80 M1 cycle (approximately equivalent to every instruction)"}].

Any new implementation would require 4 x 8 bit (or 2 x 16 bit) registers for start and end addresses, 2 x 8 bit (or 1 x 16 bit) registers for the counter, an operation code and any 8 bit value to be used in ANDing / ORing or X-ORing. Plus suitable instructions to manage these new registers and a "go" command. Also consideration is needed as to what happens if an interrupt occurs during a block operation. Do we just ignore it, or halt the block move/copy and return control to the CPU section?

Mark
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paulb
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Re: New Acorn 8bit? Should there be one?

Postby paulb » Fri Mar 31, 2017 2:44 pm

1024MAK wrote:Plus suitable instructions to manage these new registers and a "go" command. Also consideration is needed as to what happens if an interrupt occurs during a block operation. Do we just ignore it, or halt the block move/copy and return control to the CPU section?


I'm going to keep beating the drum for DMA here, which I think is far more workable than trying to extend the CPU. What I have in mind is a memory-mapped DMA register which initiates a transfer when written to, bringing RDY# low and thus locking the CPU out when it tries to read the next instruction. The DMA engine could actually fetch the transfer descriptor from memory itself.

So you would write the location of a descriptor to the DMA register, maybe something in zero page for even more simplicity. For instance:

Code: Select all

LDA #&70: STA &FC80


Then, the DMA engine would issue reads for the source, destination and length. Finally, it would execute the transfer. It would look like this as pseudo-code:

Code: Select all

source = read(descriptor); descriptor++;      # source stored at &70
destination = read(descriptor); descriptor++; # destination stored at &71
length = read(descriptor)                     # length stored at &72

while (length > 0)
{
    data = read(source);
    write(destination, data);
    length--; destination++; source++;
}


Interrupts wouldn't be serviced during this exercise because RDY# would still be low. However, you could introduce a test for IRQ# or NMI# and suspend any transfer if either signal went low.

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1024MAK
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Re: New Acorn 8bit? Should there be one?

Postby 1024MAK » Fri Mar 31, 2017 2:51 pm

This link explains the Z80 LDDR, LDIR instructions clearly. An extract is here:
cpcwiki wrote:LDIR and LDDR

This is a block copying function, it is used to transfer data from one part of memory to another fast.
  • HL must be pre-loaded with the start address
  • DE must be pre-loaded with the destination address
  • BC must be pre-loaded with the length of data
LDIR

LDIR operation:
  • read byte from memory address pointed to by HL and write it to the memory address pointed to by DE
  • Increment HL by 1
  • Increment DE by 1
  • If BC=0 then increment PC by 2 (otherwise don't increment it)
LDDR

LDDR operation:
  • read byte from memory address pointed to by HL and write it to the memory address pointed to by DE
  • Decrement HL by 1
  • Decrement DE by 1
  • Increment Program counter by 2
  • If BC=0 then increment PC by 2 (otherwise don't increment it)

NOTES
  • An interrupt can occur while a LDIR/LDDR is being executed.
  • If the LDIR/LDDR opcode is overwritten by itself then command execution will stop. Effectively, the LDIR opcode is repeatedly fetched and decoded for each byte fetched from memory.
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