Ethercat packet forwarding with distributed clocking

摘要

An EtherCAT packet forwarding system with distributed clocking is provided. The system comprises a master device and a plurality of slaves. The master comprises a processing port and a forward port for being respectively coupled to the at least two Ethernet ports of the master device in a redundant ring topology. The slaves comprise an internal clock indicating a current time, and a slave memory comprising a processing timestamp variable, a forwarding timestamp variable, a temporary timestamp variable and a copy-direct bit.

主权项

1. A packet forwarding system, the system comprising:
a plurality of slave devices, each slave device comprising
a processing port and a forward port coupled to ports of a master device in a redundant ring topology,an internal clock configured to provide a current time, anda slave memory storing a processing timestamp variable, a forwarding timestamp variable, a temporary timestamp variable and a copy-direct bit, wherein the system is configured togenerate a header of a frame datagram for each slave that comprises a circulating bit indicating whether the redundant ring topology is interrupted,when the frame datagram is received at the forward port of a slave device and the copy-direct bit is set, the current time is copied to the forwarding time stamp variable and the copy-direct bit is reset,when the frame datagram is received at the forward port of the slave device and the copy-direct bit is not set, the current time is copied to the temporary time stamp variable,when the frame datagram is received at the processing port of the slave device, the current time is copied to the processing time stamp variable and if the circulating bit indicates that the redundant ring topology is not interrupted, the copy-direct bit is set, and if the circulating bit indicates that the redundant ring topology is net interrupted, the temporary timestamp variable is copied to the forwarding timestamp variable.