Hard Real-Time Communication Protocol Design And Implementation Based On Ethernet

The main requirements of real-time communication systems are predictability of message transmission and operational flexibility. Most of these systems rely on fieldbuses to interconnect the set of nodes. However, there are three major drawbacks in fieldbuses. With an increase in the quantity and functionality of the nodes, and the requirements of dynamic environments, the traditional fieldbuses are pushed to their limits. Ethernet was found to be a good alternative. Ethernet has the advantages of fast speed, low cost, convenience of installation and good compatibility. But by the use of its CSMA/CD and store and forward, it is not suitable to provide time-bounded service.To solve the above problem, this paper presents a hard real-time communication protocol based on shared Ethernet named TTEP. The existing approaches proposed by other people, either require specialized hardware, or provide probabilistic timeliness guarantees, or are inflexible concerning the communication requirements. In the new protocol, there is no need of modifying the hardware of Ethernet. The TTEP protocol utilizes the methods of master/slave transmission, online admission control and online scheduling. It is oriented to message, and provides the guarantee of hard real-time communication. And it schedules not only the transmission but also the production, supports dynamic changes in the communication requirements, and supports of node and stream addition and removal. It converts periodic message into aperiodic message, directly or indirectly.The current TTEP prototype is implemented on an AMD Athlon(tm) 64 machine running Linux-2.6.15. For some of the interrupts such as the APIC timer interrupt and NIC interrupt, interrupt handling procedures are directly set in the interrupt descriptor table, in order to provide deterministic interrupt response time. In order to obtain the precise control of the transmission, Loacl APIC timer is used. Experiments show that this protocol guarantees the timeliness for hard real-time communication, provides high bandwidth utilization, and meets dynamic changes in the communication requirements with guaranteed timeliness, dynamic addition and removal of nodes and messages. However, there are some drawbacks which should be improved. The further related work is how to reduce the jitter of the messages.