USB2 vs, USB3

[bjlockie]

I have a COMFAST CF-953AX that I thought was connected as USB3 but when I checked it was USB2.
It is on my Raspberry Pi4.
A USB3 port connects to my USB3 hub which connects to a harddrive and USB3->nvme adapter and my Comfast.
A USB2 port connects to a KVM.

lsusb -t showed the harddrive and nvme were on bus2 which is USB3 but the Comfast was on bus1 which was USB2.

I didn't know a device could change busses ignoring how it is connected.
This is irritating.

I rebooted a couple of times and it is on bus2 now.
Can it change busses without rebooting?
I want it to stay on bus2.

[morrownr]

I guess the planets aligned and USB3 quit working today. I am testing a rtl8812bu based adapter in an x86_64 system and I can't get USB3 working. It has worked in previous tests.

USB3 is not mankind's finest effort. And then there is our good buddy, the USB3 hub chipset in the RasPi4B.

Can it change busses without rebooting?

I got nothing.

[fhteagle]

I was having all kinds of stability issues with CF-953AX making an AP. Per @morrownr 's suggestion, putting it straight into a USB2.0 (black) port of the Rpi4, no hubs, etc in between has improved stability by at least an order of magnitude.

HTH.

[morrownr]

@fhteagle

In the last 4 years, I have seen many USB3 capable wifi adapters have problems on the Pi4B. All signs point to problems in the Pi4B usb subsystem:

• The Pi4B usb subsystem should be able to supply up to 2800 mA of juice per spec but it can only provide 1200 mA. This is just really bad engineering.

• The USB3 hub chipset appears to have one or more bugs and that evidently can't be fixed with software.

If you keep a light load on the usb subsystem and you turn off other uses of electric power, you can see reasonably stable operation. My Alfa ACM can and does operate well on a Pi4B in USB3 mode. I keep scatter gather off but it can feed up to around 400 Mbps on the 5 GHz band.

One of my secrets is that if I am going to run the Pi4B as an AP, then the only adapter will be a USB3 wifi adapter or maybe I will add a WiFi 4 only adapter to a USB2 port but those will be the only items on the USB subsystem. I run my Pi's headless so as to keep any other drain off of the USB subsystem. I also shut down as many other parts of the Pi that I can.

My CF-951AX will and is running stable in the 5 GHz band in a USB3 port. It is how I am testing the beta of the WiFi 6 hostapd.conf file that is shown on the Main Menu. The adapter is the only thing in a USB port. I use a right angle usb adapter to allow it to be vertical to help with range. I turn many other users of electricity in the Pi off. I use the USB3 port that is on the same plane as the motherboard as it is more stable... probably because it is subject to less interference. I run my Pi's upside down as that works better for many reasons but I won't elaborate here.

Overall, the single biggest reasons users have problems with USB on Pi's is that they plug too many things into the usb ports. You have to limit what you do with the usb subsystem to be successful.