On Sat, 29 Feb 2020, James wrote: > On 2020-02-29 11:12 a.m., Alan Stern wrote: > > On Fri, 28 Feb 2020, James wrote: > > > > > >> $ lsusb -t > >> /: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M > >> /: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M > >> |__ Port 1: Dev 6, If 0, Class=Vendor Specific Class, > >> Driver=rtl88x2bu, 480M > >> > >> bcdUSB 2.10 > >> Means it's USB2, right? > > > >> How reliable is this? > > Quite reliable. However, on occasion something goes wrong when a > > USB-3 device is plugged in. For some reason the USB-3 connection > > fails; when this happens the device switches over to the USB-2 > > connection and then communicates at the lower speed. It still works, > > but in a degraded manner. > > > > > If something went wrong would it still say bcdUSB 2.10? A good question. According to the USB-3 specification, it would still say bcdUSB >= 3.00. But some devices might not behave that way. > It's marketed as USB 3 and it is important to have the bandwidth because > it is a network device. The bandwidth is different from the USB version. In any case, the information you want is in the Binary Object Store descriptor. Here's the information you posted originally: > Binary Object Store Descriptor: > bLength 5 > bDescriptorType 15 > wTotalLength 0x0016 > bNumDeviceCaps 2 > USB 2.0 Extension Device Capability: > bLength 7 > bDescriptorType 16 > bDevCapabilityType 2 > bmAttributes 0x00000002 > HIRD Link Power Management (LPM) Supported > SuperSpeed USB Device Capability: > bLength 10 > bDescriptorType 16 > bDevCapabilityType 3 > bmAttributes 0x00 > wSpeedsSupported 0x0006 > Device can operate at Full Speed (12Mbps) > Device can operate at High Speed (480Mbps) > bFunctionalitySupport 1 > Lowest fully-functional device speed is Full Speed (12Mbps) > bU1DevExitLat 10 micro seconds > bU2DevExitLat 1023 micro seconds The wSpeedsSupported bitmap indicates that the device will only communicate at USB-2 speed; it doesn't support SuperSpeed Gen1 (5000 Mbps) or Gen2 (10000 Mbps). FYI, the USB-3.0 specification includes this sentence (section 3.2.6.1): A USB 3.0 peripheral device must provide support for both SuperSpeed and at least one other non-SuperSpeed speed. So the fact that the RealTek doesn't support SuperSpeed operation, combined with the fact that it reports its USB version as 2.10, indicates that it really isn't a USB-3 device. What this says about the bandwidth is for you to judge. Alan Stern
