Usb hub and control method of usb hub

A USB (Universal Serial Bus) hub comprising:

• an upstream USB port connecting to an upstream device via an upstream USB line;
• a downstream USB port connecting to a downstream device via a downstream USB line;
• a clock generation circuit supplying a clock;
• a clock pin that supplies the clock received from the clock generation circuit for operating the downstream device to the downstream device;
• and
• a hub controller that automatically stops clock supply to the downstream device via the clock generation circuit and the clock pin, both when a connection between the upstream USB port and the upstream device is disconnected and when the hub controller receives a power save mode request to the downstream USB port from the upstream device,
• wherein the hub controller stops the clock supply whenever a stop of the data communication between the upstream device and the downstream device is detected by the hub controller including when the hub controller receives the power save mode request to the downstream USB port from the upstream device to stop the data communication,
• wherein when stopping the clock, the hub controller instructs the clock generation circuit to stop the clock supply and the clock generation circuit stops the clock supply from all the clock pins, and
• wherein the hub controller turns on a power line included in the downstream USB line and starts the clock supply to the downstream device when the upstream USB port and the upstream device are connected.