Sideband Signal Power Management for USB Devices
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Solution Overview
Problem
Portable computers face challenges in implementing aggressive power management for USB devices due to insufficient information exchange between USB devices and power management entities, preventing the CPU from entering low power states when USB devices are attached.
Innovation Solution
The implementation of sideband signals between the computer system and USB devices allows communication and power state management, enabling both systems to enter low power states even when one is in a low power state, with data buffering to ensure seamless data transfer upon returning to normal power states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If USB devices are attached to the host controller, then data exchange functionality is enabled, but the CPU cannot enter low power states
Solution Approach 1:
The patent introduces sideband signals as an intermediary communication channel between USB devices and the host controller. This separate signaling path allows the host controller to monitor USB device activity without requiring the main PCI bus to remain active, enabling the CPU to enter low power states while USB functionality is preserved. The sideband signals act as a mediator that decouples the power state requirements of the CPU from those of the USB subsystem.
2Reliability
If the host controller keeps the PCI bus active for USB devices, then USB communication is maintained, but power consumption increases
Solution Approach 1:
The patent segments the USB communication function into two separate channels: the main USB data bus for actual data transfer and a separate sideband signaling path for presence and activity notification. This segmentation allows the PCI bus to be powered down while USB devices remain detectable through sideband signals, reducing power consumption while maintaining communication reliability when needed.
3Device complexity
If portable computers use USB only interface for power management, then simplicity is maintained, but aggressive power management cannot be implemented
Solution Approach 1:
The patent makes the host controller universal by giving it dual functionality: it handles both traditional USB data communication and power management monitoring through sideband signals. This multi-functionality allows the host controller to implement aggressive power management strategies without requiring separate dedicated hardware interfaces, thus maintaining simplicity while improving power management efficiency.
Data Source
AI summary
In various embodiments, a computer system may include a computer controller to send and/or receive sideband signals to/from a USB device. In some embodiments, the USB device may include a USB controller to send/receive sideband signals to/from the computer controller. The computer controller and USB controller may allow communications between the computer system and the USB device when either of the computer system or USB device is in a low power state. The sideband signal sent between the computer system and the USB device may trigger the other of the computer system or USB device to enter a normal power state. In some embodiments, the computer controller and/or USB controller may be further coupled to a memory to buffer data to be sent to the computer system or USB device after the computer system or USB device returns to a normal power state.