Power Savings in USB Hubs Through a Proactive Scheduling Strategy

Bikrant Das Sharma1, Abdul Ismail2, Chris Meyers3
1Rice University, 2Intel Corporation, USB Implementers Forum, 3Fresco Logic


USB has been the dominant external I/O in computing systems over the past two decades. With the increased adoption of USB-C with high data rates, USB hubs are becoming more popular. Existing power-saving mechanisms do not save much power in USB hubs when there is a steady bandwidth demand from devices. In this paper, we demonstrate significant power savings with a proactive scheduling policy for hubs. Our approach includes the introduction of a shallow U1/CL1 low-power state, resulting in better overall power savings due to the reduced entry and exit times to U1/CL1. Our results demonstrate greater power savings (on the magnitude of multiple watts) by increasing the scheduling interval up to the minimum latency tolerance across all devices connected to that hub. As USB moves to USB4 and hubs are used to connect to higher bandwidth devices, these power savings will become even more pronounced.