(new title): Hard decision, but the answer is pretty clear.

Chat about anything CX16 related that doesn't fit elsewhere
Scott Robison
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(new title): Hard decision, but the answer is pretty clear.

Post by Scott Robison »



1 hour ago, Carl Gundel said:




It's a serial port, right?  Could be used for lots of things.



Sure, it could. A recent demo where it was used to generate video proves that. But it was never designed as a general purpose IO port. Maybe someone would repurpose it, but a more general purpose solution seems like it would be better than recreating IEC for the sake of nostalgia.

BruceMcF
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(new title): Hard decision, but the answer is pretty clear.

Post by BruceMcF »



37 minutes ago, Scott Robison said:




Sure, it could. A recent demo where it was used to generate video proves that. But it was never designed as a general purpose IO port. Maybe someone would repurpose it, but a more general purpose solution seems like it would be better than recreating IEC for the sake of nostalgia.



Though whatever that more general purpose solution runs the risk of being denounced as "feature creep".

One thing it would have been would have been pretty cheap and easy to include, since IEC handling code would have been in the original KERNAL source that they licensed. Unless I get a clone of a 1581, the only things I can see using it for is sneaker-netting things between a C64 and a CX16 using an IEC2SD, and seeing if some IEC emulation code for a modern microcontroller plugged into the user port as a server of some sort can be used to allow the CX16 to load the client side installation routine direct from the microcontroller.

Lasagna
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(new title): Hard decision, but the answer is pretty clear.

Post by Lasagna »


Lurker here! Hello all. 

The X8 is great, but if you look at the open source ZX-UNO (which has been forked with a VGA version), you get everything the X8 has plus you get real game ports, 512K of SRAM, PS/2 port, and an expansion port!

It would probably be trivial to change the game ports on the UNO to SNES style controllers if that is what David wants.

To me the X8 feels like a design constrained by the skills of the FPGA designer - someone knows the X16 FPGA (I forget is it Xilinx? Lattice?) and that specific FPGA toolchain really well and is shoehorning the design into that FPGA when we could have all the things we want, memory, real ports, and expansion, going with a ZX-UNO forked solution.

And the cost would likely end up about the same.

I will buy an X8 as soon as it is released if David chooses to release it, but I will always be annoyed by the fact the design was unnecessarily constrained by the selection of the FPGA and there were plenty of templates that the X8 could have been built off of (ZX-UNO, etc.)

 

BruceMcF
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(new title): Hard decision, but the answer is pretty clear.

Post by BruceMcF »



8 hours ago, Lasagna said:




Lurker here! Hello all. 



The X8 is great, but if you look at the open source ZX-UNO (which has been forked with a VGA version), you get everything the X8 has plus you get real game ports, 512K of SRAM, PS/2 port, and an expansion port!



In other words, you get the X16e, except with a different processor family, a different video system, and a different audio system. The various prices of ZX Uno board builds I see in a quick google are €100-€150, which subtracting VAT and doing the exchange is about $100-$150.


8 hours ago, Lasagna said:




To me the X8 feels like a design constrained by the skills of the FPGA designer - someone knows the X16 FPGA (I forget is it Xilinx? Lattice?) and that specific FPGA toolchain really well and is shoehorning the design into that FPGA when we could have all the things we want, memory, real ports, and expansion, going with a ZX-UNO forked solution.



And the cost would likely end up about the same.



Sure, it might "feel" like that to you, but going with thinking it through instead, the idea that it was designed the way it was because the designer was not sufficiently skilled to design a CX16e is not really that likely.

At present, the X16e CANNOT be designed, because the board that it emulates is only in the prototype stage.

So it seems reasonably clear that the X8 was a proof of concept, showing how much of the X16 as it existed could be fit completely into the FPGA that they were using.

Compared your "he tried to do the X16e but he's not skilled enough to succeed" theory, the proof of concept theory is actually plausible. When they came up with the "three phase" approach, they would want to know how much it would cost. Seeing how far the Vega FPGA alone could go would be a valuable piece of information to judge which larger FPGA in the family would be needed.

It also would give them a data point on whether to freeze the Vera feature set, since giving in to clamoring to make it more of a 16/32 bit era video chip would impact the size of the FPGA as well.

As far as the cost ending up the same, no, almost certainly not. If you move from a ZX-Uno or CX16e type system to the X8, the price is going to fall substantially. The 16Xe might be a touch cheaper, since the ZX Uno has a Z80 core, which is a lot bigger than a 65c02 core. But the estimate of the X8 being half the cost of an X16e ... therefore under half the cost of a ZX Uno ... seems reasonable.

Indeed, the ZX-Uno could be seen as one more argument for dropping the ZX-Uno / CX16e type "two chip" device and doing a "one chip" device instead. While not compatible with the CX family, the equivalent of a CX16e has already "been done". The X8 is far more like being breaking fresh ground.

Lasagna
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(new title): Hard decision, but the answer is pretty clear.

Post by Lasagna »



8 hours ago, BruceMcF said:





Quote




In other words, you get the X16e, except with a different processor family, a different video system, and a different audio system. The various prices of ZX Uno board builds I see in a quick google are €100-€150, which subtracting VAT and doing the exchange is about $100-$150.





No the ZX-Uno already has several 6502 cores available that you could build VERA on top of within the FPGA. You would have the same processor, video subsystem, and audio system if an X8/X16 core were built on the ZX-UNO hardware.



No the ZX-Uno is usually around 70 Euros with VAT and would be much cheaper if produced in larger quantities.



https://amigastore.eu/en/650-zx-uno-zx-spectrum-based-on-fpga.html




Quote




Indeed, the ZX-Uno could be seen as one more argument for dropping the ZX-Uno / CX16e type "two chip" device and doing a "one chip" device instead. While not compatible with the CX family, the equivalent of a CX16e has already "been done". The X8 is far more like being breaking fresh ground.





X8 is already a two chip device with an ESP32 for wireless..



 



 

BruceMcF
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(new title): Hard decision, but the answer is pretty clear.

Post by BruceMcF »



1 hour ago, Lasagna said:




No the ZX-Uno is usually around 70 Euros with VAT and would be much cheaper if produced in larger quantities.



X8 is already a two chip device with an ESP32 for wireless..



Well, that's useful. I just clicked on the first two links I got, but since Google is blocked in Beijing, that was on Bing, and it can be iffy as a search engine. As you attempt to persuade the CX16 project to abandon it's project and become a ZX-Uno project instead, that kind of info would be handy.

And it's good news ... that makes it more likely that the CX16e would be on the $70 side of the range than the $100, which is encouraging ... because it implies it is more likely that the X8 would end up on the $35 dollar side of the range than the $50.

Regarding David not knowing what he is talking about when he says the X8 would cost half as much as the X16e? You're not going to convince me on that front.

Regarding the ESP32, are you sure that's intended for the finished board and is not just there for development purposes? I got excited when I saw that, but a cooler head figured it was probably just for system development and wasn't intended as part of the finished product.

picosecond
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(new title): Hard decision, but the answer is pretty clear.

Post by picosecond »



17 hours ago, Lasagna said:




To me the X8 feels like a design constrained by the skills of the FPGA designer - someone knows the X16 FPGA (I forget is it Xilinx? Lattice?) and that specific FPGA toolchain really well and is shoehorning the design into that FPGA when we could have all the things we want, memory, real ports, and expansion, going with a ZX-UNO forked solution.



Consider the possibility that you know much less than the FPGA designer...

Of course it feels like the X8 design is shoehorned into the FPGA.  It was.  I don't know the primary motivation.  It could be cost, desire to reuse hardware or simply the fun challenge of seeing how much function could be crammed into a cheap FPGA.


17 hours ago, Lasagna said:




And the cost would likely end up about the same.



Unlikely.  The ZX-UNO RAM by itself costs about the same as the CX8 FPGA.  Everything else is kinda-sorta similar so the cost delta is dominated by the ZX-UNO FPGA.  That's 20 bucks or so in hobbyist quantities.

It's not surprising that the higher cost external RAM + bigger FPGA design point is higher function than the embedded RAM/smaller FPGA design point.  Spend more, get more.  Both designs have their merits but neither is objectively better.

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Yazwho
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(new title): Hard decision, but the answer is pretty clear.

Post by Yazwho »



45 minutes ago, picosecond said:




Consider the possibility that you know much less than the FPGA designer...



Hey now. If people start doing that there wouldn't be much of the thread left!

BruceMcF
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(new title): Hard decision, but the answer is pretty clear.

Post by BruceMcF »



1 hour ago, picosecond said:




It's not surprising that the higher cost external RAM + bigger FPGA design point is higher function than the embedded RAM/smaller FPGA design point.  Spend more, get more.  Both designs have their merits but neither is objectively better.



What is interesting is, the $35-$50 price point is chock full of little modern microcontroller SBCs, it is unfilled by that "retro FPGA systems", because the retro FPGA systems that emulate an existing system have a hard lower bound on their capabilities.

Since the X8 is an FPGA simulation of a phantom brother to the CX16 family that doesn't exist, so it doesn't have a hard lower floor on what capabilities it can provide. It is free to just provide the capabilities that fit the FPGA.

But it also justifies the reliance on the 65C02, since what is a transistor-saving design in the 70s and 80s has become a logic resource saving core in the 20s.

________________


1 hour ago, picosecond said:




Consider the possibility that you know much less than the FPGA designer...



Oh, I'm confident I know much less than the FPGA designer. That's why my primary focus is resting on one of the older tricks in the "pin saving" book, swapping decoded outputs for encoded outputs with an external decoder.

Since I don't think I can out-clever anybody in hardware design, I don't even try, and instead am just focusing on the simplest and cheapest way to make the X8 expandable, leveraging what it is already able to do.

 

BruceMcF
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(new title): Hard decision, but the answer is pretty clear.

Post by BruceMcF »



1 hour ago, picosecond said:




Of course it feels like the X8 design is shoehorned into the FPGA.  It was.  I don't know the primary motivation.  It could be cost, desire to reuse hardware or simply the fun challenge of seeing how much function could be crammed into a cheap FPGA.



Quite ... since this is a volunteer effort, even if the conversation went, "hey, what if I did a proof of concept", the fun challenge of doing it can easily be the main motivation.

I remember in grad school, some thirty years ago now, a friend of mine was helping a classmate fix a nagging problem with their Toyota pick up. I was around the gang office when the classmate dropped by to thank my friend. His answer was, "Hey, no problem, it gave me a good excuse to buy the metric tools I needed."

I didn't say anything, but it struck me at the time how that represent the "Instinct of Workmanship".

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