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USB hub status and HUB enumeration process

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Author : PURPLELEC
Update time : 2024-03-11 10:07:03
  USB hubs, like other USB devices, need to be configured when powered on. In the USB protocol, the default endpoint 0 is used. Perform communication during the initial power-on period. In addition to configuring itself, the USB hub also needs to identify other USB devices connected to the downstream port.
USB hubs
  USB hub HUB status
  USB hubs and USB host drivers query the hub's downstream port to determine whether there has been a state change. When a status change is found, the USB hub class is used to request the status and activate the device. The entire process is performed as follows:
  (1) The configuration software queries the status of the USB hub at the end of the time slice and returns the port status transition bitmap.
  (2) If the status change of the USB hub is detected, execute the GetHubStatus request to read the status change of the hub.
  (3) If it is detected that the port status of the USB hub changes, execute the GetPortStatus request to read the changes in port characteristics.
  (4) If after confirming that a USB functional device is connected to the USB port, the configuration software activates the port through the USB hub, the USB device can be used.
  USB hub HUB enumeration process
  The power-on configuration process of the USB hub is as follows:
  The USB hub is connected to the root hub of the USB host.
  The USB host reads the standard descriptor of the device and obtains the device configuration information. It contains the property information of the USB hub.
  The USB host reassigns a USB address to the USB hub device and performs enumeration such as reacquiring device descriptors.
  The USB hub powers on its downstream port.
  The USB hub detects status changes of the downstream port.
  For USB downstream ports with bus activity, read their status information.
  Activate the USB downstream port and operate the USB device connected to the downstream port.