Low-Overhead Memory Timing Adjustment with Monotonic DQ Delays
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Solution Overview
Problem
Modern DDR memory systems face increased challenges in maintaining stable throughput bandwidth due to voltage or temperature drift, leading to frequent recalibration needs during operation, which introduces undesirable overhead and increases the likelihood of errors.
Innovation Solution
Implement low-overhead periodic adjustment for memory timing by using monotonically increasing delays for individual DQ lanes, allowing for efficient data eye training with reduced overhead, aligning DQ lanes with memory IO clock, and minimizing skew through read and write leveling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequent recalibration is performed to maintain memory timing stability, then memory reliability is improved, but system overhead increases and productivity decreases
Solution Approach 1:
The system performs preliminary calibration of DQ lanes during initialization, establishing baseline timing parameters before operation begins. This preliminary action reduces the need for frequent recalibration during runtime, as the initial calibration provides a stable reference that maintains timing accuracy without requiring continuous adjustment
Solution Approach 2:
Instead of continuous recalibration, the system implements periodic adjustment mechanisms that update timing parameters at predetermined intervals or based on specific triggers. This periodic approach maintains memory timing stability while minimizing the frequency of recalibration operations, thereby reducing overhead and preserving system throughput
2Reliability
If comprehensive data eye training is performed for all DQ lanes, then data integrity is improved, but calibration overhead increases
Solution Approach 1:
The calibration process is segmented into individual DQ lane adjustments rather than treating all lanes uniformly. Each DQ lane is calibrated independently using its specific timing parameters, allowing the system to focus calibration efforts only where needed and reduce overall calibration time while maintaining data integrity for each lane
Solution Approach 2:
The system applies local quality by using individual timing parameters for each DQ lane based on their specific characteristics and positions. Rather than applying a uniform calibration approach to all lanes, each lane receives customized timing adjustments tailored to its local requirements, improving data integrity while minimizing unnecessary calibration overhead
3Manufacturing precision
If monotonically increasing delays are applied to individual DQ lanes, then skew is reduced and data eye training efficiency is improved, but system complexity increases
Solution Approach 1:
The system changes timing parameters by applying monotonically increasing delays to individual DQ lanes based on their position and characteristics. This parameter adjustment approach systematically compensates for skew without requiring complex control logic, as the monotonic progression of delay values provides a predictable and manageable method for achieving precise timing alignment
Data Source
AI summary
In an implementation, a memory subsystem may include input/output (I/O) circuitry having a data signal (DQ) group, the DQ group having multiple DQ lanes and a read data strobe, and one or more controllers coupled to the I/O circuitry, the one or more controllers being configured to assign, respectively to multiple DQ lanes of the DQ group, multiple read test delays that monotonically increase with respect to a read eye edge, read a read test value one time, using the DQ group, with the multiple read test delays respectively for each DQ lane in the DQ group, and update the read eye edge by adding a first read test delay, corresponding to a first DQ lane of the DQ lanes from the read test value that does not match a read eye training pattern, to the read eye edge to calculate a trained read eye edge.