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How would you do a multi-project chip without something like a "management engine"? By the nature of semiconductor fabrication, you have a bunch of identical c
by kragen 2y ago
How would you do a multi-project chip without something like a "management engine"? By the nature of semiconductor fabrication, you have a bunch of identical chips, but you want each contributor to the chip to be able to use it for testing their own contribution. It seems like that means you need some way to dynamically configure which of the many projects on the chip are actually connected to its I/O pins?
To clarify, since unfortunately griefers are flagging your comment to impede the discussion, so I'm not allowed to reply to it: Tiny Tapeout is a multi-project chip, not a multi-project wafer (though it is one chip in a multi-project wafer). Typical minimum die sizes are 0.8mm², which is about 2 million potential transistors in 130nm processes. That's big enough to put many projects on a chip. That's why Tiny Tapeout cost US$300 while MPW prices start at about US$3000 and more typically US$9999+.
- throwaway_3133 2y agoIt's a multi-project wafer not a multi-project chip. They cut the wafer apart into individual chips. There is one project on each chip. This has been going on since the 1970s. It is a very well-understood process.
- throwaway_3133 2y agoAll eFabless designs for the first two years of the program were multi-project wafers with single-project chips. And they still required the management engine. Over the past year they tried an experimental "multi-project chip" (first samples shipped 14 months ago). But the management engine was a requirement long before this happened. GP seems to have edited their comment, but I can't edit mine (even though it is only 8 minutes old)
- immibis 2y agoTiny Tapeout is a multi-project chip not a multi-project wafer.
- Etheryte 2y agoSidenote: On HN you can often get downvoted/flagged not only for what you say, but for the way you say it. I wouldn't really call it griefing, rather a call for more civil discussion. If an account is new or a throwaway it gets held to this standard even stronger because no one really wants to see a HN that's flooded by throwaway accounts writing Reddit style comments.
- throwaway_3133 2y ago[dead]
- kragen 2y agoThe comment in question said, "It's a multi-project wafer not a multi-project chip. They cut the wafer apart into individual chips. There is one project on each chip. This has been going on since the 1970s. It is a very well-understood process." There is absolutely nothing uncivil about that comment, and it clarified that we were talking about slightly different things, thus leading to a resolution of the apparent disagreement and, I think, broader perspective for both of us. The only even slightly uncivil thing about it would be the implication that I didn't know what MPW was, but in fact that was entirely plausible and would have been an important lacuna to correct were it true. It was an exemplary comment, and the people who flagged it so that I could not reply were being a pain in the ass for no reason.
- echoangle 2y agoWhy do you need a management engine for that? Couldn’t you just bond the connections to the ones you want and leave the other disconnected? Basically just have all chips next to each other on the die and only use one?
- danhor 2y agoI/O pads (and their drivers) take up a huge amount of space. For some simpler ICs their die size is determined by their Pads.
- mlyle 2y agoYes, Tiny Tapeout has its own MUXing layer to select which user project should be connected. The Caravel management engine is used for single project chips, but it is innocuous. It just allows debugging and probing signals, and use of common I/O structure for different user projects. You don't have to actively use it. It's hardly hidden, too: you have to instantiate it.