Understanding USB Descriptors speed

Question

I have several USB devices that are capable of running High Speed 2.0 (480 Mbps) mode but runs Full Speed 1.1 (12 Mbps) instead.

Take for example a USB DAC:

It advertise USB 2.0 compliant and fall back capability to 1.1

 SupportedUsbProtocols    : 0x03
 Usb110                  : 1 (yes)
 Usb200                  : 1 (yes)
 Usb300                  : 0 (no)

But in the device descriptor:

bcdUSB                   : 0x110 (USB Version 1.10)

Means that the manufacturer is using a IC capable of 2.0 but configured to run at 1.1?

This is not an issue but I was wondering what is the goal to run a device capable of running High Speed at lower speed. This create the need of a transaction translator and reduce overall performance.

Answer 1

For many years already, virtually all USB devices have implemented at least USB 2.0 protocol. This does not imply that they implement USB High Speed as it is optional in the USB 2.0 standard. They still profit from other USB 2.0 advances.

Implementing USB High Speed can be quite an effort for simple, inexpensive devices. The data speed cannot be handled by small MCUs. In addition, more effort needs to go into signal quality (impedance matching etc.).

Therefore, USB High Speed comes at a price and is only implemented if the device becomes more useful due to the higher speeds.