PCIe Precision Timing Measurement Uncertainty Reduction
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Solution Overview
Problem
Precision Timing Measurement (PTM) uncertainty in PCIe devices arises due to the difference in when time is measured at the components' pins and when it is processed internally, leading to diminished accuracy, especially in interconnect fabric architectures with SRIS mode and small link widths.
Innovation Solution
The PTM manager schedules PTM sequences immediately after sending SKIP ordered sets to reset the elastic buffer to a consistent state, and synchronizes PTM message exchanges with the SSC modulation cycle, ensuring consistent timing and reducing latency variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PTM sequences are processed internally after pins, then device processing capability is utilized, but timing measurement accuracy deteriorates due to processing delay variation
Solution Approach 1:
The patent applies preliminary action by resetting the elastic buffer to a known state (neutral position) before initiating PTM message processing. This is achieved by sending SKIP ordered sets to clear any residual data in the elastic buffer, ensuring that the buffer starts from a predictable state. By doing so, the processing delay becomes consistent and predictable, resolving the accuracy issue while still utilizing internal processing capability.
Solution Approach 2:
The patent changes the timing parameter by synchronizing PTM message transmission with specific phases of the SSC modulation cycle. By aligning PTM messages with particular phases where the elastic buffer is guaranteed to be at neutral position, the processing delay parameter becomes consistent. This phase synchronization approach transforms an unpredictable processing delay into a controlled, repeatable timing characteristic.
2Productivity
If elastic buffer is used for data transmission, then bandwidth efficiency is improved, but timing consistency deteriorates due to buffer depth variation
Solution Approach 1:
The patent uses preliminary action by systematically resetting the elastic buffer to neutral position using SKIP ordered sets before PTM message transmission. This preliminary reset action ensures that regardless of the buffer's previous state or depth, it starts from a known reference point, thereby guaranteeing timing consistency while maintaining the bandwidth efficiency benefits of elastic buffering.
Solution Approach 2:
The patent implements feedback by monitoring the phase of the SSC modulation cycle and using this information to determine when to transmit PTM messages. The system feedback mechanism ensures that PTM messages are only transmitted when the elastic buffer is at neutral position, creating a closed-loop control system that maintains timing consistency while utilizing elastic buffering for efficient data transmission.
3Adaptability or versatility
If PTM messages are sent at arbitrary times, then communication flexibility is improved, but timing uncertainty increases due to elastic buffer state variation
Solution Approach 1:
The patent applies periodic action by synchronizing PTM message transmission with periodic phases of the SSC modulation cycle. Instead of arbitrary timing, PTM messages are sent at regular, predictable intervals corresponding to specific SSC phases where the elastic buffer is guaranteed to be neutral. This periodic synchronization maintains timing precision while preserving communication flexibility within the structured timing framework.
Solution Approach 2:
The patent changes the timing parameter from arbitrary to phase-synchronized by tying PTM message transmission to specific phases of the SSC modulation cycle. This parameter transformation ensures that messages are sent only when timing conditions are optimal (buffer at neutral position), reducing timing uncertainty while maintaining adaptability through the periodic nature of the SSC cycle.
Data Source
AI summary
Techniques for reducing precision timing message uncertainty are described herein. A method includes resetting an elastic buffer of a first device in response to a second device linked with the first device sending SKIP (SKP) ordered sets to the first device. The method also includes initiating a PTM handshake with the second device in response to resetting the elastic buffer. Additionally, the method includes sending PTM messages to the second device immediately after receiving the SKP ordered sets.