Electronic – Is an ethernet switch considered as an ASIC

You have an absurd number of possible input sets in your input space. You can't test all of them, period. You have to test a subset of the input sets and use some worthwhile heuristic to choose the sets you do test.

Here's what your testing must do (this is derived from DO-254 test recommendations that my company uses):

• Each output must change at least once
• Each input must change at least once

That's a minimum, not a maximum. In cases like this we perform Minimum Condition Decision Coverage (MCDC) analysis to see which other input sets we need to test. I've always explained it like this:

Pretend your black box is an AND gate with 200 inputs. You can't test every single input set, so you test a subset of the whole input space. First, you follow the rules I gave above - you need to test at least two cases: one which causes the output to be 0/False and another that causes the output to be 1/True. For the AND gate this is easy: all 0/False and all 1/True. That proves your output can change. The next thing you do is to choose input sets such that there is an input set for which each input is the deciding factor in the output. For a 200 input AND gate this gives you 200 different input sets: the first one has all inputs True except for input #1, the second has all inputs True except for #2 and so on. Using this methodology you verify that each input has an independent effect on the output. If any input being False doesn't produce a False output then you know you have a problem.

You said your logic is all combinatorial. This is preferable to a whole lot of latches/flip flops but still not perfect. You have to work backwards from the output to determine input sets for which each individual input has a deciding effect on the output. If you logic is complicated then you'll have a lot of work ahead of you, but this is the quickest and most comprehensive way of testing your logic black box.

As far as the practical aspects you're on your own. The company I work for uses custom hardware to do in-system pin-level black box testing of FPGAs (and theoretically ASICs if you could provide us a part to put on a board) at operational speeds. It's comprehensive and automated but each test fixture is custom for the given project, so using this approach requires a contract and not just buying off the shelf items and combining them yourself.

One of the problems you'll have that is alleviated by our approach is simply connecting all the wires. I guess most people would suggest an obscenely large logic analyzer but you've got thousands of pins so you'd have to test subsets of pins at a time. One of the positive aspects of the approach we use is that it monitors all pins at all times so it lets you seen that the outputs you expect to change do change, but also that the outputs that shouldn't change don't either. You can't get that if you use a logic analyzer with fewer pins that the number of inputs/outputs you have.

We used an ASIC in a number of products where a microcontroller used too much power. It was a fairly simple device, a couple of hundreds gates, and had to consume less than 100 nA static, which for microcontrollers at the time was not possible. Price was comparable to a microcontroller due to high quantities; you'll probably need >100 k/yr.

An FPGA would not only have been overkill, costing a lot more, but would have needed an external code Flash, which added to the already bigger footprint.