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by exmadscientist 178 days ago
> often, what I actually need is just a little bit of weird logic that's asynchronous

As a concrete example of this: two weeks ago I wanted a 21-input OR gate. It would have been wonderful if I could spend a little bit of money, buy a programmable thing in a 24-pin package, put it down, figure out some way to get the bitstream in (this is never pleasant in medium-volume manufacturing, so it's not like we're going to solve it now), and get my gate function that is literally one line of HDL. One. Line.

As it was, a 21-input OR gate is so much work in 74-series logic that I abandoned that whole thing and we did the bigger-picture job in a different, worse, way.
2 comments
summa_tech 177 days ago
Would a SLG46880 work for you? It has 28 GPIOs, enough LUTs to make a 21-input OR gate, runs off 2.3-5.5V (two VCCIO partitions, but you can tie them together). It costs like a buck in 5k quantities - they used to be much cheaper when you bought them directly from Silego, but now that they've been acquired the price has been _improved_.

https://www.renesas.com/en/products/slg46880

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exmadscientist 174 days ago
The Silego stuff has been really attractive at high volume. This is what I think about when some of the other posters in this thread sniff at my cost expectations: this stuff can get real cheap if you have volume behind it.

It was not a fit for this use case (on this product I am literally counting tenths of pennies, so, no go), and I dread dealing with Renesas in any form, but it's the right fit for something.

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tverbeure 178 days ago
The device that you were looking was not an FPGA but a GAL22V10L.
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exmadscientist 178 days ago
No, it wasn't. Those are mostly available in PLCC and DIP packages and even if you can get the SOIC/TSSOP versions they still cost $1.20 each at 10k volume. That's flat-out unacceptable for 99% of the things I do. The entire rest of the board I was talking about was $4.60. Processor included. $1.20 is not going to fly.
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tverbeure 178 days ago
“Reduces use case and requirements to something impossibly niche and low volume then yells at the clouds.”

Anyway, just tie the output of 21 emitter followers together, add a resistor and - tadaaa - 21 input OR!

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exmadscientist 178 days ago
Hey, that was my problem from last week. And, yes, I agree with you -- it was best solved another way.

But please don't complain when I give concrete examples of things I'd like to do but couldn't. (And please do recognize that there was a lot more context to the mess than just "I need an OR gate", but no one cares about the real gory details.)

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mitthrowaway2 178 days ago
If only someone could make a single part that is very versatile, so that it could get production economies of scale while solving all the thousands of different random problems various people might have, whether they need a 21-input OR or something else. Like an array of gates, but field-programmable!

(That's a pretty steep price target even for a small FPGA though. With 16 pins maybe, but with 25?)

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