| Very nice, but my first thought was "surely this will not fit in 64k of ram!". And it doesn't. It requires a 16MB REU! To explain for the uninitiated how rare this bit of hardware is. The REU available for the c64 back in the day were 256kB and 512kB. These are most commonly built replicas as there are schematics available for them. Sometime in the late 90s there was also an "expansion" for c64 that contained a completely new CPU (superCPU - 65816) that was code compatible with the original and I believe this device could accommodate up to 16mb. Later reimplementations based purely on fpga popped up including a REU with 16mb. The original SuperCPU schematic was lost to time. Allegedly fpga based expansions are available to buy for few hundred EUR now, but I don't know anyone that attempted to buy one or has one. So, although it is a neat trick(still a cool tech achievement) , saying it runs on c64 is akin to saying I got doom3 running on a 386, but my 386 is actually a pci card in a modern pc... If I can't pull my c64 with hardware available back in the day (or hardware one could realistically built back in the day) I'm not sure saying "runs on c64" is correct. Coming back to the subject of a REU, why has no one published a schematic for one yet? There are cheap SRAM chips floating on ebay. It should be trivial to put one together. Unfortunately it isn't, because the original (Super Cpu) had two components we need a beefy fpga to emulate. The supercpu itself and it's dma controller which was a custom asic I believe. Perhaps as cheap(ER) fpgas or uC with fpga-like functionality become available someone will create an open source "super cpu". As of yet, everyone I ever heard using these, uses emulation. Nothing wrong with that, but I get the most out of my "retro hobby" by running original hardware. Emulation is very useful for dev, but for general use it's a bit "meh" for me. |
A 16MB REU could absolutely have been built in the 80s. It would have been absolutely astronomically expensive, but there’s no technical reason it could not be done. You seem to be confusing the SuperCPU with a plain REU expansion — the REU is just a bunch of RAM and an ASIC that talks to the 64 and allows it to store or retrieve banks of RAM (because obviously a 6502 cannot address more than 64K so instead you have to tell it to swap out system RAM) — there is no CPU on it.
The SuperCPU (65816) can indeed address up to 16MB directly and that is a different thing. The project in the OP runs on a stock C64 on the stock C64 CPU, it just needs a mountain of RAM that would have cost the equivalent of a house back then ;)