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I had a friend who mentioned that it was very difficult to get the 64-cores Parallellas with fully-functional Epiphany-IV chips. Are these yield problems going to continue with Epiphany-V or can we expect a full 1024 functional cores per chip?

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It would be a BIG mistake to assume 1024 working cores. If you want to scale your software you should take a look Google/Erlang and others. Not reasonable to demand perfection at 16nm and below...

Not saying we won't have chips with all cores working, just saying you shouldn't count on it.

So what can we count on?

In a tile based CPU error topology matters. A string of broken cores or a broken core at the edges is likely worse than a broken core with all 4 (or 8?) neighbors working.

Impossible to characterize without high volume silicon or accurate yield models. We can say that historically, most failures are in SRAM cells and they are limited to a few bits (core still works!) and that in general only one out of N cores will fail. For arguments sake, let's assume the while network always works, but 1 CPU may be broken. (this is what needs to be confirmed later). Does that help?

Yes, that helps.

It might be easier to work around broken SRAM bits than just skipping a whole core.

That way you could always have same pipeline layout and not need to compute it dynamically.

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