USB Host Controller Event Ring Synchronization
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Solution Overview
Problem
USB host controllers waste power due to asynchronous events causing irregular updates of the Event Ring, leading to frequent transitions between power saving and normal modes, resulting in increased power consumption.
Innovation Solution
A host controller apparatus that synchronizes the output of event information to the system memory with the timing of interrupt signals to the processor, reducing the frequency of system memory access and minimizing power usage by optimizing the timing of power mode transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the USB host controller updates the Event Ring in system memory upon each event occurrence, then event information is kept current, but power consumption increases due to frequent transitions from power saving mode to normal mode
Solution Approach 1:
The host controller pre-allocates an event ring buffer in system memory and prepares the interrupt mechanism in advance. When events occur, the controller simply writes to the pre-prepared buffer location and triggers a pre-configured interrupt, avoiding the need to dynamically allocate memory or set up complex update routines during event handling, thus reducing the time spent in normal mode.
Solution Approach 2:
Instead of updating the Event Ring continuously or on every single event, the system uses periodic interrupt moderation to batch multiple events together. The interrupt controller accumulates events in the Event Ring and only generates an interrupt to the CPU when a threshold is reached or a time interval expires, allowing the host controller to remain in power saving mode longer while still maintaining event information currency.
2Speed
If the host controller remains in normal mode to quickly access system memory for event updates, then event processing responsiveness is improved, but power consumption increases
Solution Approach 1:
The patent introduces an event ring buffer as an intermediary data structure between the USB host controller and the CPU. The controller writes event information to this buffer in system memory and sets a bit in an event status register, then returns to power saving mode. The CPU is notified via interrupt and processes events from the buffer at its own pace, decoupling the controller's event detection speed from the CPU's processing speed and allowing the controller to stay in low power mode longer.
3Use of energy by moving object
If interrupt moderation time (IMOD) is extended to reduce interrupt frequency, then power consumption decreases, but event processing delay increases
Solution Approach 1:
The system dynamically adjusts the interrupt moderation behavior based on event types and system state. Critical events can trigger immediate interrupts with shorter IMOD periods, while less urgent events are batched with longer IMOD periods. The event ring buffer allows the system to maintain a pool of pending events that can be processed quickly when the CPU becomes available, effectively making the interrupt timing adaptive rather than fixed.
Data Source
AI summary
The present invention aims to provide a host controller apparatus, an information processing apparatus, and an event information output method that are capable of outputting event information to a system memory while achieving power saving. A host controller apparatus according to the present invention includes: an event controller that outputs occurred event information to a system memory; and an interruption controller that outputs an interrupt signal to a CPU executing an event recorded in the system memory, the interrupt signal requesting execution of the event output from the event controller to the system memory. The event controller outputs the occurred event information to the system memory in synchronization with a timing at which the interruption controller outputs the interrupt signal to the CPU.