TOD Clock Oscillator Skew Calibration in Multi-Node Networks
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Solution Overview
Problem
Current systems for synchronizing Time-of-Day (TOD) clocks in IBM z-Series servers lack microsecond-level accuracy and fail to detect oscillator failures, especially in STP configurations without External Time Reference (ETR) connections, and GPS receivers do not provide the necessary precision or failure detection mechanisms.
Innovation Solution
A method that uses Hardware Management Console (HMC) to periodically obtain timestamps from an external time source and a primary-time server, computes the PRT offset, and adjusts the TOD clock by setting a fine steering rate to compensate for oscillator skew, allowing for self-diagnosis and correction of oscillator errors within specified tolerances, even in noisy environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ETR connections are used to synchronize TOD clocks, then synchronization capability is provided, but the system cannot detect oscillator failures and is unavailable in STP-only configurations
Solution Approach 1:
The system performs self-diagnosis by monitoring its own oscillator performance through periodic timestamp comparisons. The TOD clock system automatically detects oscillator failures by analyzing drift patterns without requiring external diagnostic equipment, enabling the system to serve its own calibration and monitoring needs.
Solution Approach 2:
The system implements continuous feedback by periodically comparing timestamps from the TOD clock against expected values and adjusting or flagging oscillator status based on drift analysis. This closed-loop monitoring enables automatic detection of oscillator failures while maintaining compatibility with STP-only configurations.
2Measurement precision
If GPS receivers are used for time synchronization, then external time source capability is provided, but microsecond-level accuracy and failure detection are not achieved
Solution Approach 1:
The system replaces reliance on external GPS hardware with a software-based timestamp comparison mechanism that uses existing system clocks and periodic time queries. This substitution achieves comparable or superior accuracy without requiring additional hardware, while simultaneously enabling oscillator failure detection through drift analysis.
Solution Approach 2:
The system performs preliminary calibration by accumulating timestamp data over multiple intervals before making synchronization adjustments. This preliminary data collection phase enables the system to establish baseline oscillator behavior and detect deviations that indicate failure, achieving both high precision and reliability.
3Measurement precision
If periodic timestamp sampling is performed over long intervals, then oscillator skew detection accuracy is improved, but synchronization response time increases
Solution Approach 1:
The system uses periodic timestamp sampling at optimized intervals that balance accuracy and response time. By systematically querying timestamps at regular intervals and analyzing the progression of drift, the system achieves accurate oscillator skew detection while maintaining timely synchronization response through structured periodic measurement.
Solution Approach 2:
The system performs preliminary accumulation of timestamp data over multiple intervals to build a sufficient data set for accurate skew calculation. This preliminary data gathering enables precise oscillator characterization without requiring excessively long waiting periods, as the system prepares the necessary measurement foundation in advance for rapid analysis when needed.
Data Source
AI summary
A system, method and computer program product for calibrating a Time Of Day (TOD)-clock in a computing system node provided in a multi-node network. The network comprises an infrastructure of computing devices each having a physical clock providing a time base for executing operations that is stepped to a common oscillator. The system implements steps for obtaining samples of timing values of a computing device in the network, the values including a physical clock value maintained at that device and a TOD-offset value; computing an oscillator skew value from the samples; setting a fine steering rate value as equal to the opposite of the computed oscillator skew value; and, utilizing the fine steering rate value to adjust the physical clock value and correct for potential oscillator skew errors occurring in the oscillator crystal at the computing device.