Pseudo-Synchronous Link Latency Calibration for Fixed Timing
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Solution Overview
Problem
High-speed communication systems face significant latency variations due to clock domain and data path time discrepancies, making simple source synchronous time interfaces impractical, and introducing latency uncertainty with FIFO circuits, which is unacceptable for systems requiring fixed latency at high clock speeds.
Innovation Solution
A communication system and method that determine the maximum data latency, measure actual data path latency, and compensate for the difference during calibration, ensuring a fixed total latency by adjusting subsequent data signals, allowing for pseudo synchronous communications at higher clock rates with fewer communication lines, thus reducing system costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If FIFO circuit is added to compensate for timing variations, then timing synchronization is improved, but latency uncertainty increases
Solution Approach 1:
The patent measures and records the actual data path latency during a calibration phase before normal operation begins. This preliminary measurement establishes a baseline latency value that is stored and used to compensate for timing variations during subsequent data transfers, eliminating the need for FIFO circuits that introduce uncertainty.
Solution Approach 2:
The patent replaces the mechanical/FIFO-based timing compensation mechanism with a software/firmware-based latency measurement and compensation system. By using timestamp recording and calculation rather than physical buffer circuits, the system achieves deterministic latency without the uncertainty introduced by FIFO depth variations.
2Productivity
If clock rate is increased to achieve higher data rates, then productivity is improved, but latency variation increases
Solution Approach 1:
The patent implements a feedback mechanism where the measured actual data path latency is used to adjust and compensate for timing variations in subsequent operations. The system continuously monitors and compensates for latency, allowing high clock rates to be maintained while keeping latency variations within acceptable bounds through active correction.
Solution Approach 2:
The patent changes the approach from trying to maintain fixed latency through conservative clock rate selection to actively measuring and compensating for latency parameters. By recording timestamps and calculating actual latency values, the system can operate at high clock rates while maintaining deterministic latency through parameter-based compensation rather than rate-based conservatism.
3Device complexity
If pseudo synchronous communication is used to reduce cost and simplify interfaces, then device complexity is reduced, but latency control becomes difficult
Solution Approach 1:
The patent performs preliminary latency measurement during a calibration phase before normal pseudo-synchronous communication begins. By establishing the actual data path latency in advance and storing this value for use during operation, the system maintains simple pseudo-synchronous interfaces while achieving deterministic latency control through the pre-measured compensation value.
Data Source
AI summary
A system and method compensate for latency, where the system includes a transmit module and a receive module that implements a DLL in a pseudo synchronous communications link. The method includes determining maximum data latency based on synchronous latencies and analog delays; measuring an actual data path latency by determining a delay in receiving a test pattern transmitted from the transmit module at the receive module using a common synchronization pulse provided the transmit and receive modules simultaneously or with a known fixed latency separation during calibration; determining a latency difference between the determined maximum data latency and the measured data path latency; and compensating for the latency difference for a subsequent data signal transmitted from the transmit module in the pseudo synchronous communications link, such that a total latency of the system with regard to the subsequent data signal is equal to the maximum data latency for the system.