Ruigu Electronic

A USB hub is one of the many standard devices in the USB family, classified under the HubClass standard class. A USB hub must implement the functions defined in the USB specification and has the necessary descriptors to describe its functionality.

A USB hub must implement the functions defined in the USB specification and has the necessary descriptors to describe its functionality.

A hub primarily consists of a signal repeater and a controller. The repeater transmits USB signals in the correct direction, while the controller interprets the protocol and instructs the repeater’s actions.

The hub controller is controlled by the hub through two endpoints. A USB hub uses its standard endpoint 0 for configuration and querying. This configuration pipeline implements most standard control transactions and then proceeds to implement various hub-specific control transactions.

These transactions include: ClearHubFeature, ClearPortFeature, GetBusState, GetHubDescriptor, GetHubStatus, GetPortStatus, SetHubDescriptor, SetHubFeature, SetPortFeature.

The hub has a status change endpoint to notify the host of changes in its downstream ports. If any downstream status changes occur, a port change bit is set: device connected, port enabled, suspended, overcurrent indication, reset, and powered on.

The host queries the USB hub every 255ms to report the status of its downstream devices. If nothing has changed, the hub simply returns NAK.

Status changes include: device connected, port enabled, suspended, overcurrent indication, reset, powered on, and disconnected, etc.