How many angels…

… can dance on the head of a pin?

I have no idea – but I do know how many ZPUFlex processors will fit in a DE1 dev board: 25!  [Edit: I’ve since managed to squeeze in another one – so 26!]

OK, I’m stretching things a little to claim that 25 fully-featured ZPUFlex CPUs will fit on the DE1, because these have a really tiny ROM and very minimal supporting logic, so Quartus can optimise the hell out of the design – but it still seemed like a fun demo.

Source, as always, can be found on GitHub.

[EDIT: The M4K memory blocks on the DE1’s Cyclone II support 32-bit data width, but not in full dual-port mode, where the data width is limited to 16-bit.  This means that no matter how small the ZPU’s ROM/StackRAM, it will occupy a minimum of 2 M4Ks.  If it weren’t for this fact, I think the DE1 could take 3 further ZPUs.  As it is, it’s possible to add just one more instance of the ZPU, and the code on github now reflects this.  The record for the maxmium number of soft CPUs in a single project on the DE1 board is now 26.  Unless you know diffferent!]

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