Here's some new Commodore 64 enthusiasm

[Alex Eisenhut]

Let's revel in this nostalgia!

[SiliconWizard]

And this:
https://mega65.org/

[ebastler]

And this:
https://mega65.org/

Named such because releasing it takes 65 months longer than you thought. 

[MK14]

And this:
https://mega65.org/

Named such because releasing it takes 65 months longer than you thought. 

Why does theirs run at x40 via the FPGA, but yours (65C02+) does x100, if I remember correctly ?

[ebastler]

I have not looked at their hardware in detail, but with 384k of RAM I assume that the main memory lives outside of the FPGA. (Maybe with some on-chip caching?) I cheated and used the on-chip 64k only, which helps with the speed. 

[MK14]

I have not looked at their hardware in detail, but with 384k of RAM I assume that the main memory lives outside of the FPGA. (Maybe with some on-chip caching?) I cheated and used the on-chip 64k only, which helps with the speed. 

Good point!

I hadn't thought of it like that. I'd assumed that they were mainly running as a 64K address space, with rare bank switching, setup.

On the other hand, even 384K of RAM, can still fit into bigger and more expensive FPGAs and/or super fast external SRAM, might be options ?

On the other hand, they (bigger FPGAs) can get too pricey and you might be using dual-port memory, to help speed it up.

[ebastler]

I guess most users will end up playing old C-64 video games anyway, which are best consumed at the original speed. 

[MK14]

I guess most users will end up playing old C-64 video games anyway, which are best consumed at the original speed. 

True.

x40 is still a HUGE speedup, compared to the old C64's. It must seem/feel amazing, I guess.

E.g. A Chess game that took 5 minutes a move, drops down to a much more palatable 7.5 seconds.

[SiliconWizard]

I have not looked at their hardware in detail, but with 384k of RAM I assume that the main memory lives outside of the FPGA. (Maybe with some on-chip caching?) I cheated and used the on-chip 64k only, which helps with the speed. 

I don't know about their whole design, so I can't tell for sure how they implemented memory.

But just judging from pictures of the PCB, they have used an Artix-7 100T, which is a pretty BIG fpga for this kind of application. It has a total of 4860 kbits of block RAM, which is almost 600 KBytes. So there's definite room for 384 KBytes of computer RAM in this, and then some for other uses. Yes it embeds that much memory. Oh, and you could use a fraction of the internal logic too for implementing distributed RAM on top of this.

As to clock rate, with such an FPGA, reaching 150 MHz for a 6502 core sounds definitely possible. I'm sure you could even reach 200 MHz+ if carefully designed. Now you could be limited not just by the CPU core but by all the surrounding peripherals, memory access, etc.

Actually I'm not sure why they chose such a big FPGA for this. To make it "future-proof" maybe. You could certainly implement a whole computer system including relatively complex peripherals and a much more powerful CPU too (or actually several!)

Now I'm just thinking that they may have implemented a nice video controller in it, which may take a significant amount of resources and block RAM for its frame buffer.

Also looking at pictures, we can see two chips next to the FPGA, one being an ISSI chip, which is probably either a RAM chip or a Flash chip, can't tell. The other, can't tell the vendor but it also looks like a memory chip of some kind.

But yes in theory, it's certain that with the FPGA they chose, they could have implemented a MUCH faster CPU than they did, along with a fair amount of RAM, with no external memory required. But that's their project, anyone is free to develop their own!