Precision Time Synchronization System of Embedded Devices in Distributed Subnet Network

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.