Host Controller Queue Head Trimming for USB Power Reduction
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Solution Overview
Problem
Inefficient management of queue heads in USB networks leads to unnecessary bus activity, energy wastage, and missed work opportunities, particularly when inactive queue heads are examined, causing inefficiencies and increased power consumption in battery-powered devices.
Innovation Solution
Implementing a method to trim inactive queue heads from monitoring, allowing only active ones to be polled, and reintroducing inactive queue heads when they become active, using criteria such as inactivity duration or number of monitoring events, to reduce resource consumption and bus activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the host controller examines all queue heads in round robin fashion to ensure fair service, then every queue receives attention, but inactive queues consume unnecessary power and time
Solution Approach 1:
The patent implements dynamic queue management by transitioning queues between active and inactive states based on their activity status. Active queues are monitored and serviced, while inactive queues are placed in a low-power state, allowing the system to adapt its monitoring behavior to actual workload conditions rather than using a static round-robin approach for all queues.
Solution Approach 2:
The patent applies different monitoring strategies to different queues based on their individual activity characteristics. Instead of uniformly examining all queues, the system selectively monitors only those queues that are currently active or likely to be active, applying local optimization to each queue's service pattern rather than a global uniform approach.
2Reliability
If the host controller examines all queue heads including inactive ones, then no queue is missed, but bus bandwidth is wasted on unnecessary transactions
Solution Approach 1:
The patent extracts inactive queues from the active monitoring set, separating them from the queues that require regular examination. By removing inactive queues from the monitoring list, the system eliminates unnecessary bus transactions related to these queues while maintaining the ability to service them when they become active again.
Solution Approach 2:
The patent performs preliminary classification of queues to identify which ones are inactive before the main servicing cycle begins. This preliminary action allows the system to prepare an optimized monitoring list that excludes known inactive queues, preventing wasteful bus transactions before they occur.
3Speed
If the host controller monitors all queue heads frequently, then active queues are serviced promptly, but inactive queues prevent the processor from entering low-power states
Solution Approach 1:
The patent dynamically adjusts the monitoring frequency and processor power state based on queue activity. When queues are inactive, the processor can transition to lower power states since there is no urgent work to be done. When queues become active, the system transitions back to higher-power states to handle the workload, creating a dynamic power management strategy that responds to actual system conditions.
4Reliability
If the host controller examines every queue head in memory, then all potential work is identified, but time is lost on queues with no activity
Solution Approach 1:
The patent extracts inactive queues from the examination process, removing them from the list of queues that require time-consuming memory inspections. This extraction maintains work detection completeness for active queues while eliminating the time waste associated with examining queues that have no pending work.
Solution Approach 2:
The patent applies partial examination action by monitoring only a subset of queues (those that are active or likely active) rather than examining all queues in memory. This partial approach is sufficient to identify all actual work that needs to be done, avoiding the excessive action of examining every single queue regardless of its activity status.
Data Source
AI summary
Methods and apparatus for enhancing efficiency (e.g., reducing power consumption and bus activity) in a data bus. In an exemplary embodiment, methods and apparatus for intelligently trimming (and adding or re-adding) queue heads resident in a host device associated with various client device processes are disclosed. By selectively trimming inactive or dormant queue heads, the host expends less resources and time polling the queue heads during routine operations. Similarly, queue heads which are newly active, or acquired are intelligently added to ensure proper bus operation. Inactive queue heads are brought back into the polling process only when requested, thereby keeping the list of queue heads to be polled or examined as short as possible at all times.