Amiga custom chips on an FPGA?

[Radertified]

This was mentioned on the Amiga Discord. I think it's an interesting idea.

We can get reproduction motherboards, Kickstarts, keys, cases and PSU's, but when it comes to the custom chips, nothing? Why isn't there FPGA recreations of each of the Amiga's custom chips?

For example, if I wanted to upgrade the Agnus in my Amiga, I could flash the FPGA, remove my original and replace with the new one. Done.

I'm not an electronics person so I don't know if this is a completely insane idea, but from a software point of view, the code for the chips exists as part of Minimig.

Perhaps people already do this and I haven't heard about it

[robinsonb5]

That's the general idea behind this project: https://github.com/nonarkitten/amiga...cement_project
I don't know how far along they are, though.

The biggest problem from a hardware point of view is just that 5v-tolerant FPGAs aren't exactly common, so any particular board would need to include level translators.

Also note that the Indivision ECS scandoubler effectively re-implements Denise in pretty much the way you have in mind.

[Daedalus]

Terrible Fire was working on just such a replacement for Agnus before he gave up his Amiga work.

[Radertified]

Originally Posted by robinsonb5

That's the general idea behind this project: https://github.com/nonarkitten/amiga...cement_project
I don't know how far along they are, though.

The biggest problem from a hardware point of view is just that 5v-tolerant FPGAs aren't exactly common, so any particular board would need to include level translators.

Also note that the Indivision ECS scandoubler effectively re-implements Denise in pretty much the way you have in mind.

I know nonarkitten is getting close with her Buffy Accelerator (Discord) which is a drop-in replacement for the 68000. She's been talking about implementing the code lately and has estimated a few more months before a beta is released.

As I said, I'm not an electronics guy so I didn't know that about the 5v-tolerant FPGAs. Sounds like an obstacle, but what do I know?

The problem with the Indivision, other than availability, is it's not cheap. I would think that a direct replacement for the chips would be significantly cheaper than that.

[robinsonb5]

Originally Posted by Radertified

I know nonarkitten is getting close with her Buffy Accelerator (Discord) which is a drop-in replacement for the 68000.

Ah, I saw that mentioned recently but didn't know who was behind it - cool, thanks for the info

(And why hasn't it been talked about in depth on eab? Did I just miss it?)

As I said, I'm not an electronics guy so I didn't know that about the 5v-tolerant FPGAs. Sounds like an obstacle, but what do I know?

It's not insurmountable, it just makes things messier and increases the component count. See the four chips either side of the main chip on the Buffy? They're there to solve the same problem.

The problem with the Indivision, other than availability, is it's not cheap. I would think that a direct replacement for the chips would be significantly cheaper than that.

Agreed - I mentioned it just to show that no, it's not an insane idea, and there is precedent.

[Radertified]

Originally Posted by Daedalus

Terrible Fire was working on just such a replacement for Agnus before he gave up his Amiga work.

It's a shame to lose developers and projects

Originally Posted by robinsonb5

Ah, I saw that mentioned recently but didn't know who was behind it - cool, thanks for the info

(And why hasn't it been talked about in depth on eab? Did I just miss it?)

It's not insurmountable, it just makes things messier and increases the component count. See the four chips either side of the main chip on the Buffy? They're there to solve the same problem.

Agreed - I mentioned it just to show that no, it's not an insane idea, and there is precedent.

I haven't heard of Buffy being talked about at all here, but maybe I just missed it too. I heard about it via the Amiga discord where nonarkitten used to frequent.

Glad I'm not talking insane talk I've got my fingers crossed the Amiga's future is in cheap, easily reproducable (and maybe even upgradeable) chips.

[S0ulA55a551n]

Are FPGAs not kind of expensive to be drop in replacements for these chips?

At one point I believe Jens was working on something kind of similar, not sure if was going to be drop in replacements for existing machines though

[Daedalus]

Custom chips are only getting more expensive as they're a finite resource and demand is increasing. The Agnus variant from the A3000 in particular is tricky to get hold of, and often commands a high price as a result. Since these sorts of hobby projects rarely cover development costs in terms of labour, the cost of such a replacement won't be all that huge. IIRC, the FPGA that TerribleFire was using for his Agnus replacement was only £5. Other chips may require more expensive FPGAs, but it's not really *that* crazy money-wise, considering Analogic sell NOS Alice chips for £65 each, for example, and the more common A500+ Agnus chip for £45.

[torsti76]

Originally Posted by S0ulA55a551n

Are FPGAs not kind of expensive to be drop in replacements for these chips?



At one point I believe Jens was working on something kind of similar, not sure if was going to be drop in replacements for existing machines though

Jens is working with Dave Haynie to create an updated "Buster 12". This project aims not only at making new Busters but also at fixing the remaining bugs, e.g. with multiple busmasters.

The new buster, while FPGA based, according to Jens will be a drop in replacement that fits the PLCC socket.

As for the cost, there are two things worth considering:

- Stock is not endless. For Buster and Alice in particular, it's hard to find a seller now. And because reserves are low and demand is high, prices go through the roof. A well-known UK store is meanwhile charging GBP 60 + shipping for a NOS Buster 11. For this kind of money you can buy 2 large FPGAs which brings me to the second point

- Amiga custom chips are primitive by today's standards. Most of the AGA chips would fit comfortably in a decent CPLD. Some, like Alice, are more demanding and would need a FPGA instead. Also, with the more complex ones you have to consider possible timing problems, existing support circuitry etc.

One of the main culprits in doing all this is that many of the original documentation is long lost. Thus you need very skilled and knowledgeable people to recreate the chips. And that is the most expensive part of the undertaking in my opinion...

[S0ulA55a551n]

Originally Posted by Daedalus

Custom chips are only getting more expensive as they're a finite resource and demand is increasing. The Agnus variant from the A3000 in particular is tricky to get hold of, and often commands a high price as a result. Since these sorts of hobby projects rarely cover development costs in terms of labour, the cost of such a replacement won't be all that huge. IIRC, the FPGA that TerribleFire was using for his Agnus replacement was only £5. Other chips may require more expensive FPGAs, but it's not really *that* crazy money-wise, considering Analogic sell NOS Alice chips for £65 each, for example, and the more common A500+ Agnus chip for £45.

Interesting, didn't realise they had got so cheap. I guess you only need pretty small number of gates to replicate just a single chip

[eXeler0]

Originally Posted by Radertified

This was mentioned on the Amiga Discord. I think it's an interesting idea.

We can get reproduction motherboards, Kickstarts, keys, cases and PSU's, but when it comes to the custom chips, nothing? Why isn't there FPGA recreations of each of the Amiga's custom chips?

For example, if I wanted to upgrade the Agnus in my Amiga, I could flash the FPGA, remove my original and replace with the new one. Done.

I'm not an electronics person so I don't know if this is a completely insane idea, but from a software point of view, the code for the chips exists as part of Minimig.

Perhaps people already do this and I haven't heard about it

I hear you.. in fact.. check this thread started by me ;-)
http://eab.abime.net/showthread.php?t=105107
..and its not really a novel idea. I think Jens of iComp looked at this alot when he first started planning the 1200 reloaded. Some AGA chips are easy to find others are not.. so to have a product that can be produced in volume there needs to be a plan for how to handle potential custom chip shortages.. so FPGA re-implementations were considered. Buuuuut... the economics need to make sense too.. as long as actual replacement chips are available they will be used instead..
But speaking of Jens, there was some news recently about Dave Haynie helping Jens develop a Buster replacement in FPGA, so..

at some point in the future I wouldn't be surprised if this happens.. but it will be "because why not" instead it being a wise and cost effective solution.
As you can see, the FPGA used in Vampires can fit a lot in one FPGA and at the same time get rid of a lot of the architectural bottlenecks.. and being one FPGA, it makes more sense economically..

That being said.. I'm a big fan of odd "because why not" projects, so I too hope we see this some day ;-)

[idrougge]

Jens has been working on this for several years with his CloneA chipset. I think the Indivision ECS is an offshoot of that project.

[NovaCoder]

Originally Posted by idrougge

Jens has been working on this for several years with his CloneA chipset. I think the Indivision ECS is an offshoot of that project.

Clone A was finished years ago and even demonstrated, it was just canned like so many projects.

My ideal Amiga replacement motherboard would feature a real 68K CPU and an FPGA to replicate the custom chips. You could actually design a replacement A1200 motherboard that used an FPGA and modern electronics with a processor slot that was compatible with existing 68K accelerators. This approach would result in a very cost effective way to build a modern A1200 replacement system. We already have new cases and keyboards.

If you also recreate the CPU in FPGA you have a MiSTer (which is what I'm using!)

The original MiniMig project got it right!

[dreadnought]

Far as I know, Minimig is not a 1:1 perfect recreation.

[AJCopland]

Originally Posted by dreadnought

Far as I know, Minimig is not a 1:1 perfect recreation.

No, but it could be a place to start. Something to build upon so you'd get a mostly working system to begin with.

[AJCopland]

There's the A1200+ project which could be used to put each of the custom chips onto swappabale daughter boards. http://www.amigaclub.be/projects/amiga1200plus

You'd put all of the custom chips in, then repalce one of them with FPGA, implement the design for the chip. Then move onto the next chip.