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USB 3.2 testing is darn hard! We talk compliance test specs, USB 3.2 testing BKMs, and pre-spec silicon. Guest Jit Lim sits down with Mike Hoffman and Daniel Bogdanoff to talk about the new difficulties engineers are facing as they develop USB 3.2 silicon.
Agenda:
In the last electrical engineering podcast, we talked about how USB 3.2 runs in x2 mode (“by two”)
This means there’s a lot of crosstalk. The USB Type C connector is great, but its small size and fast edges means crosstalk is a serious concern.
When we test USB, we want to emulate real-world communications. This means you have to check, connect, and capture signals from four lanes.
For testing Thunderbolt you always have to do this, too.
Early silicon creators and early adopters are already creating IP and chips for a spec that isn’t released yet.
2:00 They’re testing based on the BKM (Best Known Method)
3:30 Jit was just at Keysight World Japan, where many people presented BKMs for current technologies. Waiting for a test spec to be released is not an excuse for starting to work on a technology.
4:50 How many companies are actually developing USB 3.2 products? The answer isn’t straightforward – the ecosystem is very complex and there are multiple vendors for a single system (like a cable).
6:30 Many USB silicon vendors will develop an end-product and get it certified to prove that their silicon will work. They then sell the silicon and IP to other companies for use in their products.
7:50 Daniel listened to an interesting podcast about how Monoprice reverse engineers complex products and sells them for cheaper:
https://www.npr.org/sections/money/2014/11/28/366793693/episode-586-how-stuff-gets-cheaper
9:40 There are some BNC cables at the Keysight Colorado Springs site that were literally wire pulled and built in the building.
10:00 Has anything changed as USB technology advances? There are a lot of new challenges – multiple challenges, retimers, multiple test modes
Testing retimers is nontrivial, they are full receivers and full transmitter.
11:30 When a new spec is developed, what does that look like? How far does the test group go when setting a new spec?
The spec doesn’t look at how to test, it just looks it what it should do.
Then, there’s a compliance test specification (CTS). This is developed by a test group, that looks at how things should be tested.
So, there are two groups. the first asks “what should the spec be?” and the second asks “how do we test that group?”
13:30 How many people are testing USB 3.2? Even though the compliance test specification is not developed yet? There are non being shipped, but there is a lot of activity!
14:30 What are the main challenges? Basics. When you have 10 Gbps over copper on a PCB, people are failing spec! There are issues with some devices passing only intermittently. Especially over long cables and traces.
15:45 Cheap PCBs make things even more tricky. So, there’s very sophisticated transmitter equalization and even moire sophisticated receiver equalization. It’s crucial to keep the low cost PCB material and processes to keep the overall end-product cost low. Using higher end materials would dramatically increase the cost of consumer products.
17:30 The first TV Mike bought was after his internship at Intel. He bought a $30-ish 1080i TV for $1600. Now, you couldn’t give away that TV.
18:30 Stupid questions for Jit:
What is your favorite national park and why?
What is your favorite PCB material and why?
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Just found this podcast! Love the content. Good amount of technical information. Kind of wish the episodes were longer, but appreciate the effort :).
Thanks! Glad you enjoy it!