Adaptive Control Loop Protection for PCIe Link Recovery
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Solution Overview
Problem
High-speed PCIe link designs face challenges in maintaining robustness due to noisy data during entry and exit from low-power states, leading to link degradation or failure, and increased exit latency, which reduces power and performance benefits.
Innovation Solution
Implementing an early EIOS pattern detection mechanism to freeze control loops speculatively and unfreeze them in a staggered sequence, using a digital Finite State Machine to manage loop states and enable loops only after valid exit detection, thereby preventing error propagation and ensuring stable link recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feedback control loop reacts to noisy data during entry and exit from power states, then the control loop attempts to correct the noisy signals, but this unsettles the loop to values that are not optimal for electrically robust link operation
Solution Approach 1:
The patent extracts the control loop from the noisy data environment by detecting entry into low-power states and suspending control loop updates during this period. This separation prevents the noisy data from affecting the control loop, allowing the loop to maintain stable, optimal values without reacting to transient noise during power state transitions.
Solution Approach 2:
The patent performs preliminary detection of low-power state entry conditions before the actual power state transition occurs. By detecting the entry condition in advance and proactively suspending the control loop, the system prevents noisy data from unsettling the loop before the noise even occurs, maintaining stability throughout the transition.
2Stability of the object's composition
If the control loop is suspended during low-power state entry and exit, then link stability is maintained, but exit latency increases reducing power management benefits
Solution Approach 1:
The patent applies partial suspension of the control loop by selectively disabling only the update mechanism while keeping the control loop structure intact. The loop filter coefficients are frozen rather than fully resetting the loop, allowing for faster recovery compared to complete loop suspension, thus reducing exit latency while maintaining stability.
Solution Approach 2:
The patent changes the operational parameters of the control loop during low-power states by freezing the loop filter coefficients to their current values rather than resetting them. This parameter preservation allows the loop to resume quickly upon exit from low-power state, minimizing latency while preventing noise-induced instability during the transition.
3Productivity
If high data transfer rates are used in PCIe links, then productivity is improved, but signal distortion increases reducing communication reliability
Solution Approach 1:
The patent utilizes feedback from the control loop that continuously monitors signal quality and adjusts equalization parameters. This feedback mechanism compensates for signal distortion at high data transfer rates by dynamically optimizing receiver settings, thereby maintaining communication reliability even as productivity increases through higher speeds.
Solution Approach 2:
The patent implements dynamic adjustment of control loop parameters and equalization settings based on real-time signal conditions. By making the system adaptive rather than static, it can optimize performance for high data transfer rates while automatically compensating for the increased signal distortion that accompanies higher speeds, maintaining reliability across varying operating conditions.
Data Source
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AI summary
Methods and apparatus related to adaptive control loop protection for fast and robust recovery from low-power states in high speed serial I/O applications are described In some embodiments, a first bit pattern is detected, at a first agent, that indicates a speculative entry by a second agent into a low power consumption state and one or more control loops are frozen. A second bit pattern is detected (after entering the low power consumption state) that indicates exit from the low power consumption state by the second agent and the one or more control loops are unfrozen (e.g., in a specific order). Other embodiments are also claimed and/or disclosed.