Media Clock Synchronization Using CRF Frames and PTP Timestamps
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Solution Overview
Problem
Existing time-sensitive networking technologies face challenges in synchronizing multiple talker devices and listener devices, such as microphones and speakers, to ensure precise media playback across automotive and theater applications, as they struggle with varying propagation delays and clock signal synchronization.
Innovation Solution
A network interface device generates and transmits clock reference frames based on IEEE 1588 PTP to synchronize the clock signals of multiple talker devices with a media subsystem, using IEEE 1722 CRF frames, and recovers a media clock for precise media playback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional time synchronization methods are used to synchronize multiple talker devices and listener devices, then clock signal synchronization can be achieved, but varying propagation delays cause imprecision in media playback synchronization
Solution Approach 1:
The patent introduces an intermediary mechanism (timestamp values in CRF frames and phase measurement blocks) that mediates between the grandmaster clock and follower devices. This intermediary allows each device to independently measure and compensate for its specific propagation delay, thereby achieving precise synchronization despite varying delays across the network.
Solution Approach 2:
The patent implements feedback through timestamp measurements and phase comparisons. Follower devices continuously measure the phase difference between received CRF frames and their local clocks, then adjust their clocks accordingly. This closed-loop feedback mechanism enables precise compensation for propagation delays and maintains synchronization accuracy.
2Adaptability or versatility
If packet-based time synchronization is used to synchronize clock signals across multiple devices, then scalability is improved, but device complexity increases due to CRF frame generation and processing
Solution Approach 1:
The CRF frame structure serves multiple functions simultaneously: it carries timestamp information for synchronization, includes phase measurement data for delay compensation, and provides a standardized format compatible with IEEE 1588 PTP. This multi-functionality reduces the need for separate synchronization protocols and simplifies device architecture while maintaining scalability.
Solution Approach 2:
The patent uses timestamp copying from the grandmaster clock to follower devices through CRF frames. Each follower device copies the timestamp values and uses them to reconstruct the grandmaster clock phase locally, eliminating the need for complex real-time clock distribution while achieving accurate synchronization.
3Measurement precision
If clock reference frames are transmitted at high rates to achieve precise synchronization, then phase and frequency synchronization accuracy is improved, but network bandwidth consumption increases
Solution Approach 1:
The patent transmits CRF frames at a moderate rate (e.g., 300 Hz or 1 kHz) rather than at the full media sample rate. This partial action approach provides sufficient synchronization accuracy for most applications while significantly reducing network bandwidth consumption compared to transmitting synchronization data at every audio sample.
Solution Approach 2:
The CRF frames contain preliminary timestamp and phase information that allows follower devices to pre-calculate synchronization adjustments before media playback. This preliminary action enables accurate phase and frequency synchronization without requiring high-rate continuous transmission, as devices can interpolate between CRF frame updates.
Data Source
AI summary
Examples described herein relate to a network interface device comprising: a direct memory access (DMA) circuitry; a device interface; a network interface; and a circuitry to: transmit a clock reference frame to multiple talker devices at a predefined rate to cause the multiple talker devices to synchronize clock signals with a time stamp value in the clock reference frame. In some examples, the circuitry is to synchronize a leading edge of a media clock signal based on the time stamp value and provide the media clock signal to an media processing system.