嵌入式裝置於分散式子網路節點之精確時間同步系統

Precision Time Synchronization System of Embedded Devices in Distributed Subnet Network

趙逸群(I-Chung Chao)

指導教授 ： 張帆人

共同指導教授 ： 涂昆源

國立臺灣大學/電機資訊學院/電機工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.02907

摘要

網際網路的蓬勃發展，不僅方便了人們的日常生活，更影響分散式系統的重要性。本論文架構在嵌入式平台遵從IEEE 1588 標準規範，引用不同的控制法則，讓不同主從( Master – Slave )節點的振盪器頻率相同，其亦使主從兩端時間高精度地同步。
IEEE 1588是高精度時間同步協定( Precision Time Protocol, PTP )，適用於分散式網路系統各節點之即時時間同步。時間伺服器是PTP的核心。利用主時鐘( Master Clock )與從時鐘( Slave Clock )的時脈偏差值當作回饋信號，透過控制法則，讓從節點的振盪器頻率緊隨著主節點振盪器，不斷地微幅調整。嵌入式系統強大的客制化及網路能力，受到分散式系統的青睞。本論文分析了計算機與分散式網路之間的相關細節，並整合實作出於分散式嵌入式架構下的同步系統。
本論文使用精確時間協定常駐程式( Precise Time Protocol daemon, PTPd )開放性原始碼，並對其設計雙輸入單輸出之模糊控制器，採用主從端之間的時脈偏差值以及累積時脈偏差值作為其輸入，而輸出為調整Linux核心之系統時間的頻率參數。在分散式的嵌入式主從架構環境下，透過修正型亞倫方差( Modified Allen Deviation )進行模糊控制器與比例積分控制器運行下的頻率穩定度分析，以及時域暫態收斂時間的比較；最後提出交換式控制器( Switching Controller )的概念：整合模糊法則與比例積分法則成為模糊比例積分( Fuzzy Proportional Integral, FPI )交換式控制器。FPI交換式控制器改善了原來的PI控制器之暫態收斂時間過長的缺點，而保留了PI控制器頻率穩定的優點。

關鍵字

時間同步系統 ； 高精度時間同步協定 ； 模糊控制 ； 切換式控制器 ； 分散式嵌入式系統

並列摘要

As the progress of internet, not only people feel convenient but also the distributed systems become popular. The implementation of embedded platforms which are designed according to IEEE 1588 standard for high precision synchronizing systems is investigated in this thesis. Moreover, we improve the performance of system response, that is, the clock offsets from the master to the slaves, by different control schemes.
IEEE 1588, i.e. Precision Time Protocol (PTP), is suitable for distributed network system. The time servo is the core of PTP, in which the clock offsets between the master and the slaves are used to adjust the slave clock so that their oscillators have the same frequency. The powerful embedded systems become more and more important due to their abilities of customizing and networking.
The Precise Time Protocol daemon (PTPd) is used to maintain the synchronized real-time clock system among the nodes of a distributed network. The fuzzy controller in the daemon is proposed. Its two inputs are clock offsets from the master to the slaves and the summation of clock offsets. Its one output is the argument of the system call of Linux operating system for tuning the clock frequency. Within a distributed embedded system, Modified Allen Deviation is used to analyze the stability of clocks. The comparision of stability of clocks between fuzzy controller and PI controller is mentioned. Also, the time responses are discussed. Moreover, the concept of switching controller is proposed. The integrated fuzzy controller and the PI controller are named FPI (Fuzzy Propotional Integrate) controller. The long transient time is reduced in the FPI controller via the operations of fuzzy function. The steady state frequency stability of the FPI controller is reserved via the operations of the PI function.

並列關鍵字

Time Synchronization System ； Precision Time Protocol ； Fuzzy Control ； Switching Controller ； Distributed Embedded System

參考文獻

[1] International Telecommunication Union Telecommunication Standardization Sector (ITU-T), G.811, “Timing characteristics of primary reference clocks”, Sept. 1997.

[3] H. Weibel, “High Precision Clock Synchronization according to IEEE 1588: Implementation and Performance Issues,” in Proc. Embedded World 2005.

[4] IEEE Std 1588-2002, IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems, 8 November 2002.

[7] J. C. Eidson, “IEEE-1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems: Test and Measurement Applications,” Proceedings of the 2005 Conference on IEEE-1588 Standard, Zurich, Oct. 2005.

[12] N. Barendt, K. Correll, “Design Considerations for Software Only Implementations of the IEEE 1588 Precision Time Protocol,” Proceedings of the Conference on IEEE 1588, Zurich, Oct. 2005.