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Comment by wmf | Hacker News Reader

They do build prototypes and test them.

Yep, and the highest data rates are only really possible on the best processes (12nm, 7nm, 5nm) , which is a fun chunk of change to spend for a tape out.

...using very, very expensive equipment.

Modern high end serdes have very complex signal mgmt and monitoring tools built in. You can detect the link quality, pull eye diagrams/etc from them.

So a lot of the reason for using some of these high end scopes/analyzers is bypassed by the testing/diagnostics functions on the serdes itself. And then of course there are a ton of signal tuning parameters which get programmed during link training.

Even modern analyzers have problems with this, and I've seen vendors that instead of even trying to reconstruct the signal at the endpoint use virtual transmission models and require one to probe at the source.

This is one of those areas that I bump into every couple years, and its frequently quite educational.

I wonder how flexible the serdes built in test equipment stuff is.

A BNC-to-PCIe-lane board with some signal conditioning would make for a hilarious oscilloscope.

You better make isolation a subpart of 'some signal conditioning' or you'll be looking at some expensive repairs. That's the hard part of making a scope: isolating the source and the scope guts while maintaining signal integrity.

>BNC

This makes me smile. When I left PHY testing a few years ago SMA was no longer keeping up with the > 25 GBaud PAM4 standards coming out.

BNC was useful for PHY development in the 90s.

I suspect it's heavily sampled, and maybe not only on the time axis. They would already have a reconstructed clock available, so it would be straightforward to sync up a time aperture, and the voltage aperture could be swept by adding an offset into the output comparator(s). They could then scan the ranges of both parameters to build up the eye diagram with minimal additional hardware. This would make it a brilliant oscilloscope if you want an eye diagram of a high speed serial bus, but for just about any other task it would be a bit rubbish. There isn't a UXR hiding in every PCIe 5+ lane.

That's likely how it is. It would still be interesting if there was something like a glscopeclient driver for them.

If nothing else it would make hardcore overclockers step up their game and start talking more about signal integrity. :)

Haha, yes, I'd love to see what slathering vaseline on a high speed diff pair does to the eye. Link equalization is the real MVP! It'll be fun to see how this evolves with 32Gbps and PAM4.

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