安全关键性分布式系统时钟同步机制及算法研究

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摘要

嵌入式系统在经济和技术方面取得的巨大成功，导致许多应用的计算机系统

部署日趋增多，甚至在计算机失效可能导致严重后果的领域也是如此。FlexRay 线

控转向系统是安全关键性分布式系统，对通信网络要求很高，既要满足常规的控

制要求，又要具有超高可靠性和强实时性。时钟同步作为分布式系统的核心机制

之一，在 FlexRay 网络的实时性方面扮演重要角色，有关它的研究已经成为安全关

键性分布式系统研究的一个重要组成部分。

本文首先分析了 FlexRay 总线协议及其与时钟同步相关的同步帧、时间层次、

通信循环等概念，然后深入研究了 FlexRay 时钟同步过程中在节点间实现本地时间

交换、偏差值计算、收敛函数、相位校正和速率校正的方法。

为了提高时钟同步精度，本文研究了影响分布式时钟同步精度的各种因素，

深入分析了时钟同步过程中的传输延时不确定性和时钟漂移，结合 FlexRay 时钟同

步机制，提出了传输延时测量法和新的速率偏差计算方法。传输延时测量法通过

在节点间互发同步报文，由本地节点获取同步报文到达的时间戳，然后在同步报

文的负载段传输时间戳信息，并给出了 FlexRay 节点根据时间戳计算传输延时的公

式。FlexRay 速率偏差值计算仅依据奇偶循环相位偏差值之差进行计算，具有偶然

性，本文针对这个问题设计了相位偏差趋势方程，其权值即为时钟漂移率，并给

出了利用最小二乘法求解权值的公式和实现程序，以连续时间间隔代替即时时间

间隔，达到提高时钟同步精度的目的。

为了提高 FlexRay 系统的稳定性，本文引入了相位偏差状态图的概念，根据状

态图的权值变化情况，实时、动态地评价同步节点的时钟同步性能及网络的稳定

性，找出性能较差的同步节点，然后对该节点的速率修正值进行调整，使它尽快

与其他同步节点保持同步。

最后，以 FlexRay 线控转向系统作为平台，本文给出了有效提高 FlexRay 线控

转向系统时钟同步精度的节点配置和网络配置方法及实现流程。

关键词：时钟同步 FlexRay 时钟漂移相位偏差状态图

ABSTRACT

With the great success of Embedded systems in in economy and technology, more

and more computer systems are being used for applications, even those field in which if

computer failure occurs, there will lead to serious consequences. Steer-by-wire system

of FlexRay is Safety-Critical system，it has higher requirements on the communication

network. The communication network should not only meet Conventional control

requirements,but also should meet the requirements including high fault-tolerance,

reliability and real-time performance.. Clock synchronization is one of the core

mechanism of Distributed Systems， it play an important role in real time system, and

the research on it has already become an important part of research of Safety-Critical

system.

In this paper, the research of FlexRay protocol are the basis of a detailed study

about the FlexRay clock synchronization frame、time hierarchy communication and so

on Then This paper introduce the ways of nodes how to exchange local time, how to

calculate deviations, how to use the Convergence function and how to handle the phase

correction and rate correction.

Through the research of the factors which influence the clock synchronization

precision,this paper mainly analysis the uncertainty propagation delay and clock drift.

Then combined FlexRay clock synchronization mechanism, this paper propose two

ways to improve FlexRay clock synchronization , they are transmission delay

measurement method and the improved rate deviation calculation method. The

Propagation delay measurements is : synchronization nodes exchange synchronization

frame, nodes abtain the local timestamps of action points, then send t the corresponding

timestamps throuth payload segment of synchronization frame , also give the formula of

transmission delay of FlexRay node according to the time stamp

FlexRay rate deviation calculation is only based on the difference between the

value of the even cycle phase deviation and odd cycle phase deviation ,in this way there

wll have great fluctuations, in order to solve this problem,this paper establish phase

deviation trend equation,,and its weight is the clock drift rate. Then use the least squares

method for solving equations and give the program of achieving the weitht at last ,this

way use continuous time intervals instead of instantaneous time separations to improve

precision of clock synchronization.

In order to inprove the stability of FlexRay system,this paper introduces the

conception of state diagram based on offset difference, in this way synchronization

performance of sync nodes and stability of network can be evaluated instantaneously

and dynamically according to the change of weight coefficients in state diagram Then

find the poor performance node of the synchronization system and improve node rate

correction value to maintain it synchronization with the other synchronization node

synchronization. as soon as possible.

At last,based on the platform of FlexRay steer-by-wire system,this paper give the

effective configuration of synchronization nodes communication network parameters

and implementation process.

Key words: Clock synchronization，FlexRay，Clock drift

Phase deviation state diagram

摘要

ABSTRACT

第一章绪论 ........................................................ 1

1.1 研究背景与意义..................................................................................................................... 1

1.1.1 安全关键系统的概念 ...................................................................................................... 1

1.1.2 分布式系统的由来及优点 .............................................................................................. 4

1.1.3 分布式系统的时钟同步 ................................................................................................. 5

1.2 时钟同步研究现状 ................................................................................................................ 5

1.2.1 时钟同步的国外研究现状 ............................................................................................. 5

1.2.2 时钟同步的国内研究现状 ............................................................................................. 7

1.3 安全关键性分布式系统时钟同步研究基础平台 ................................................................ 8

1.4 本论文所做的主要工作 ........................................................................................................ 9

第二章时钟与时钟同步 ............................................. 10

2.1 时钟 ...................................................................................................................................... 10

2.1.1 物理时钟和参考时钟 ................................................................................................... 10

2.1.2 时钟漂移和时钟失效 ................................................................................................... 10

2.1.3 时钟精密度与时钟准确度 ........................................................................................... 12

2.2 时钟同步 .............................................................................................................................. 12

2.2.1 内部时钟同步............................................................................................................... 13

2.2.2 外部时钟同步............................................................................................................... 13

2.2.3 时钟同步方式............................................................................................................... 14

2.2.4 同步条件 ...................................................................................................................... 15

2.3 时钟同步算法...................................................................................................................... 16

2.3.1 Lamport 逻辑时钟同步算法 ......................................................................................... 16

2.3.2 Cristian 时钟同步算法 .................................................................................................. 18

2.3.3 中央主节点同步算法 ................................................................................................... 19

2.4 时钟同步过程...................................................................................................................... 19

2.4.1 读取时间 ...................................................................................................................... 20

2.4.2 收敛函数 ...................................................................................................................... 21

2.4.3 状态修正与速率修正 ................................................................................................... 21

2.5 本章小结 ............................................................................................................................. 22

第三章线控转向系统 FlexRay 时钟同步机制 ........................... 23

3.1 线控转向系统安全关键性设计 .......................................................................................... 23

3.1.1 线控转向系统硬件冗余 ................................................................................................ 23

3.1.2 线控转向系统可靠性 ................................................................................................... 24

3.2 FlexRay 系统的分布式时钟同步 ........................................................................................ 25

3.2.1 FlexRay 系统的时间等级与时间层次 ......................................................................... 25

3.2.2 FlexRay 系统的全局时间和本地时间 ........................................................................ 26

3.2.3 FlexRay 同步帧配置原则 ............................................................................................ 26

3.3 FlexRay 系统的时钟同步 .................................................................................................... 27

3.3.1 FlexRay 时钟同步进程 ................................................................................................ 27

3.3.2 FlexRay 时钟偏差值测量 ............................................................................................ 29

3.3.3 FlexRay 时钟修正值计算 ............................................................................................ 29

3.3.4 FlexRay 时钟修正 ......................................................................................................... 32

3.3.5 FlexRay 时钟同步程序 ................................................................................................ 32

3.4 本章小节 ............................................................................................................................. 33

第四章 FlexRay 线控转向系统时钟同步算法改进 ....................... 35

4.1 影响时钟同步精度的因素 .................................................................................................. 35

4.1.1 传输延时不确定性 ....................................................................................................... 35

4.1.2 时钟的不稳定性 ........................................................................................................... 36

4.2 传输延时法 FlexRay 时钟同步算法改进 .......................................................................... 37

4.2.1 FlexRay 传输延时配置 ................................................................................................. 37

4.2.2 传输延时改进算法 ....................................................................................................... 39

4.3 时钟漂移率 FlexRay 速率偏差计算改进 .......................................................................... 40

4.4 本章小结 ............................................................................................................................. 43

第五章 FlexRay 时钟同步性能动态检测及实现 ......................... 44

5.1 相位偏差状态图.................................................................................................................. 45

5.1.1 相位偏差曲线............................................................................................................... 45

5.1.2 相位偏差状态图定义 .................................................................................................... 45

5.2 同步节点动态检测法 .......................................................................................................... 46

5.3 线控转向系统时钟同步配置及实现 .................................................................................. 50

5.3.1 节点报文传输配置 ....................................................................................................... 50

5.3.2 网络参数配置................................................................................................................ 51

5.3.3 同步报文发送与接收 ................................................................................................... 53

5.4 本章小结 ............................................................................................................................. 55

第六章结论与展望 .................................................. 56

6.1 课题工作总结...................................................................................................................... 56

6.2 课题研究展望....................................................................................................................... 56

参考文献 ......................................................... 58

在读期间公开发表的论文和承担科研项目及取得成果 .................... 61

致谢 ............................................................ 62

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摘要：

摘要嵌入式系统在经济和技术方面取得的巨大成功，导致许多应用的计算机系统部署日趋增多，甚至在计算机失效可能导致严重后果的领域也是如此。FlexRay线控转向系统是安全关键性分布式系统，对通信网络要求很高，既要满足常规的控制要求，又要具有超高可靠性和强实时性。时钟同步作为分布式系统的核心机制之一，在FlexRay网络的实时性方面扮演重要角色，有关它的研究已经成为安全关键性分布式系统研究的一个重要组成部分。本文首先分析了FlexRay总线协议及其与时钟同步相关的同步帧、时间层次、通信循环等概念，然后深入研究了FlexRay时钟同步过程中在节点间实现本地时间交换、偏差值计算、收敛函数、相位校正和速率校...

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