USB HUB Chip Solution (for Engineers)

[inches]

I've been researching parts and pieces for a build of my own (a topic for another day). Recently, [mention]Kite[/mention] and [mention]Helder[/mention] have been helpful in sharing some of their experiences with me. While talking to [mention]Helder[/mention], I learned of a limitation to the FE1.1s USB chip and I wanted to share what I found through some research.

~~~
TL;DR - Don't use the FE1.1s because multiple USB devices of different speeds mess it up. Use the FE1.1 instead. See Single Transaction Translator(STT) and Multiple Transaction Translator (MTT)
~~~

I found the datasheet for the FE1.1s and a sample schematic from @Helder

(Alt schematic and more discussion here: https://forum.sparkfun.com/viewtopic.php?f=42&t=37320

Then @Helder shared that he was experiencing issues with the hub when a WiFi dongle was used. He explained that when you have a keyboard and mouse along with a WiFi dongle, the devices weren't acting quite right. What he did to get around that was to limit the speed of the WiFi dongle to USB 1.1.

I needed a USB HUB, and this chip didn't seem worth the trouble. So I began to search around for other open source designs. I didn't find anything open source to note, but I did come across the Zero4U USB HUB for the Pi Zero and noticed that it made use of the FE1.1s also!

By chance the product page on Adafruit mentioned that it only works on the PiZeroW with a ferrite ring installed. Hmm..that rings a bell. The PiZeroW has WiFi...could that be related to why @Helder was having issues when a dongle was introduced?

The company has a page up explaining that the WiFi signals were so close to the USB pads that they were causing interference. Their solution was to place a big ferrite ring around the pogo pins attaching it to the Pi, thus reducing the radio interference from the radio.

All these facts lead to one conclusion, that Zero4U is being interfered by the WiFi radiation, and that interference is introduced via the two pogo pins on PP22 and PP23, which are very close to the WiFi antenna on Raspberry Pi Zero W. When there are more network activities, the WiFi radiation becomes stronger, and the two bare pogo pins will work as antenna and receive some high frequency noise, which will make Zero4U unstable and fail.

Was that the issue @Helder was having? I'm not exactly sure, as I'm not testing things out, but I think @Helder said it didn't solve it.

There's something else I discovered while researching the FE1.1s. The seemingly official company product page of the chip lists several variations of it. FE1.1s, FE1.1, FE2.1, and FE4.1.. These are mostly variations on how many USB ports you can expand to, but I was curious about the difference between the FE1.1 and the FE1.1s. The datasheets looked almost exactly the same except for one paragraph that stuck out. One said it was a Single Transaction Translator (STT) and the other Multiple Transaction Translator (MTT).

Off to Google to figure out what the heck that means.
Single Transaction Translator(STT) and Multiple Transaction Translator (MTT)

Question:
what is the difference between Single Transaction Translator(STT) and Multiple Transaction Translator (MTT)

Answer: A USB hub has two choices for organizing Transaction Translators (TTs). A hub can have one TT for all downstream facing ports that have full-/low-speed devices attached ( called Single Transaction Translator---STT) or the hub can have one TT for each downstream facing port ( called Multiple Transaction Translator---MTT) .
[...]
If downstream USB devices are either all high-speed or just a single full-/low-speed device a lower cost, a Single Transaction Translator (STT) hub can be considered. If the application is multiple full-/low-speed devices with a need for bandwidth, a Multiple Transaction Translator (MTT) hub should be used. In the case of consumers connecting full-/low- speed devices with USB 2.0 hubs that use Single Transaction Translator (STT) technology, they are bound to face performance issues when multiple USB devices are used.

So the FE1.1s is bound to face performance issues when multiple USB devices are used, eh? That pretty much sounds exactly like the issues @Helder was having. So just use the more expensive MTT version?

Again, I haven't actually tested any of this out, but it would seem that if anybody is interested in using this USB HUB, they should try using the FE1.1 rather than the FE1.1s. It comes in a QFP package rather than SSOP, and is about twice as expensive (~$1.00 vs ~$0.50). Given that you apparently can't use the STT hub for devices not rated exactly the same as each other it certainly seems worth it. I haven't found a USB chip otherwise that's in the price range. Anybody else?

Additionally, does it sound necessary to add some EMI filters to any traces intended for WiFi to keep the interference indicated by the Zero4U HUB's issues from causing issues?

What do you guys think?

[inches]

Thinking further, it makes sense that it worked for @Helder when he arbitrarily ran his WiFi dongle at USB 1.1. @Helder, was your keyboard USB 1.1? If so, then you effectively made the devices the same speed, which then works fine on STT.

Can you see if the wifi works fine using newer USB 2.0 keyboards?

[abrugsch]

good work!

[Helder]

Thinking further, it makes sense that it worked for @Helder when he arbitrarily ran his WiFi dongle at USB 1.1. @Helder, was your keyboard USB 1.1? If so, then you effectively made the devices the same speed, which then works fine on STT.

Can you see if the wifi works fine using newer USB 2.0 keyboards?

That is the conclusion I came to after we spoke that they were the same speed. My keyboard worked fine in 2.0 speed as well as 1.1 but many people didn't have such luck hence why I had a list of working keyboards on my support thread.

Another thing that might be wise to consider my controller chip the Atmega32u4 is hardwired in to one of the usb ports on the chip and I'm very positive (but could be wrong) that's it's a 2.0 device. The reason I mention this is that before lowering the speed on the pi for this hub chip many people have used the wifi dongle along with usb 2.0 keyboards and still had issues with the wifi working properly.

Maybe EMI interference like you posted the link to on adafruit?