Touch Input Timing Synchronization to Reduce Display Latency
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Solution Overview
Problem
Interactive devices experience latency due to the time required to process input information and refresh displays, which can only redraw at fixed frequencies, causing a wait period before new information can be displayed, leading to increased system latency.
Innovation Solution
The system synchronizes input capture and processing with display refresh cycles by timing rendering to coincide with the next refresh, ensuring the most recent input events are included, and estimates rendering times based on complexity and system workload to minimize latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the display refreshes at fixed frequencies, then the display system can maintain stable operation, but latency increases due to the wait period before new information can be displayed
Solution Approach 1:
The system performs preliminary actions by capturing input events and pre-processing rendering data before the display refresh cycle begins. The rendering engine prepares graphics frames in advance during the display update period, so that when the refresh occurs, the processed information is ready for immediate display, eliminating the wait period while maintaining fixed refresh frequency stability
Solution Approach 2:
The system dynamically adjusts the timing of input sampling and rendering operations to coincide with display refresh cycles. By synchronizing the rendering engine with the display controller, the system optimizes when processing occurs within each refresh period, reducing latency while preserving the stable fixed-frequency operation of the display hardware
2Loss of time
If the system processes input information quickly, then latency is reduced, but the complexity of coordinating with display refresh cycles increases
Solution Approach 1:
The system implements feedback mechanisms where the rendering engine receives timing information from the display controller about upcoming refresh cycles. This feedback allows the processor to adjust its processing schedule dynamically, completing input sampling and rendering operations just in time for the next refresh, thereby reducing latency while managing complexity through intelligent coordination rather than rigid scheduling
Solution Approach 2:
The system employs periodic action by aligning all input sampling and rendering operations with the display's fixed refresh period. By organizing processing tasks to occur in regular intervals synchronized with refresh cycles, the system simplifies coordination complexity through predictable, periodic timing patterns while maintaining fast response times
3Loss of time
If the display refresh rate is increased, then latency is reduced, but energy consumption increases
Solution Approach 1:
The system performs preliminary rendering and input processing during the display update period before the refresh occurs. By completing as much processing work as possible in advance during the frame buffer update time, the system reduces the need for higher refresh rates to achieve low latency, thereby lowering energy consumption while maintaining fast visual response
Data Source
AI summary
Disclosed are systems and methods for decreasing latency between an acquisition of touch data and processing of an associated rendering task in a touch sensitive device having a touch sensing system capable of producing touch data at a touch sampling rate and having a display system that displays frames at a refresh rate. In an embodiment, the system estimates at least one of (a) a period of time for sampling touch data from the touch sensing system, (b) a period of time for computing touch event data from sampled touch data, and (c) a period of time for rendering of a frame to a frame buffer. The system determines a period of time Tc for (a) sampling touch data from the touch sensing system, (b) computing touch event data from sampled touch data, and (c) rendering of a frame to a frame buffer, based at least in part on the estimate. The system determines a point in time Tr at which the display system will be refreshed from the frame buffer. A sampling start time is computed based at least in part upon Tr and Tc. Sampling of the touch sensing system is initiated to obtain sampled touch data at the sampling start time. Touch event data is computed from the sampled touch data, and a frame that reflects the touch event data is rendered to the frame buffer prior to the time Tr. The display is then refreshed from the frame buffer.