If you ever thought that a faster hub with a faster uplink would fix your USB 2 device speed problems – USB-IF engineers, apparently, thought differently and you might have to find a workaround for your “many cheap SDRs and Pi 4 in a box” setup.Īs a fun party trick, since USB 3 device enumeration only uses USB 2 as fallback, you can, in theory, connect eight devices to a four-port USB 3 hub – four USB 2 devices and four USB 3 devices.
Even if you have a USB 3 hub plugged into a USB 3 port, multiple USB 2 devices plugged into it still cannot break through the USB 2 uplink limit of 480 MBps. There’s many implications to this that are counterintuitive if you simply take “USB 3.0” for “faster backwards-compatible USB”, and they have painful consequences.įor instance, USB 3 hub ICs have two separate hub entities inside – one for USB 3 and one for USB 2. USB 3 uses two single-directional differential pairs, akin to PCI-E, whereas USB 2 uses a single bidirectional one, and the two interfaces on a blue connector operate basically independently of each other. When you see a blue “3.0” port, it’s actually USB 2 and USB 3 - two separate interfaces joined into a single connector. It might be puzzling – why is this even needed? It’s about the little-known dark secret of USB3, that anyone can deduce if they ever have to deal with a 9-pin USB 3.0 connector where one of the three differential pairs doesn’t quite make contact. If you have a USB 2.0 device and a host with only USB 3.0 signals available, this chip is for you. The VL670 is a chip that addresses a surprising problem – converting USB 2.0 signals into USB 3.0. On Twitter, has found and highlighted an intriguing design – a breakout board for the VL670, accompanied by an extensive yet very easy to digest write-up about its usefulness and inner workings.