gGoncçalomb MB >: .compt


Check your connections

2021-03-31T21:21:49+00:00 • goncalomb • usb,rpi

After some time trying to debug why I was getting degraded performance from an HDD connected to my Raspberry Pi 4, I found that it's possible to physically connect USB 3 type A connectors incorrectly...

If not plugged all the way in, there's a chance that only 4 of the contacts meet, and we get USB 2 speeds. This is possible because the extra 5 conductors required for SuperSpeed are on the tip of the plug and are the last to connect, the other 4 are for backward compatibility with USB 2 and power.

Did some extra testing and apparently it's also possible to insert the connector slowly enough that we get USB 2 speeds even with the connector fully inserted. The connection is not 'promoted' to USB 3 after the extra contacts meet. Probably won't surprise anyone that knows the USB protocol.