Who doesn't need Ethernet timestamps?
External MAC- or PHY-layer hardware timestamp
Since many legacy products use microcontrollers together with FPGAs, adding the TSU to the FPGA and the remaining modules to a microcontroller can reduce development costs. The FPGA serves as an external hardware timestamp assist to run the higher layer modules in a microcontroller. While this implementation will not match the performance of an integrated hardware timestamp, it is close and sometimes less costly.
For example, laboratory tests of an evaluation board for a Freescale PowerQUICC processor with an FPGA doing the timestamp function gave a timestamp resolution of 40 ns with standard deviation +/- 25 ns and maximum deviation +/- 200 ns.
Similarly, hardware timestamps can be performed in an external PHY to give excellent low-nanosecond resolution. In this case, the PHY is the closest device to the wire, so it can provide accuracies similar to those seen with integrated hardware timestamps solutions.
For example, laboratory tests of an evaluation board for the Freescale MCF5234 ColdFire processor with a National Semiconductor Precision PHYTER® doing the timestamp function gave a timestamp resolution of 8 ns with standard deviation +/- 12 ns and maximum deviation +/- 80 ns.
Hardware timestamps with accuracies better than 500 ns may be considered for applications such as:
• Test and measurement
• Industrial automation for synchronous applications such as machine and motion control, industrial networking, vision and scanning systems
• Electric power monitoring and switching for transmission substation integrated protection, system control and data acquisition. Accurate time synchronization of control systems helps maximize network efficiency and aid in disaster recovery because the network is able to operate closer to capacity and coordination and reporting can be centralized. Outage durations are minimized when faults are diagnosed remotely.
• Equipment monitoring for preventative maintenance of large turbo machinery, nuclear plants and electrical power plants
• Public Safety Answering Points (PSAPs)
• Ethernet-based audio/video bridging (AVB) is a developing standard that specifies the protocol, data encapsulations and procedures used to ensure that audio and video-based end stations can communicate and interoperate using standard lower layer networking services that meet the requirements for time-sensitive applications.
• Laser measurement systems
• Radio frequency identification (RFID)
• Communication satellites require accurate time synchronization to perform direct-to-home digital television and wireless communication
• Planetary spacecraft for low earth orbit (LEO) and geostationary orbit (GEO) satellites
• Printing machinery for time synchronization of machine functions to improve throughput
• Synchronization of sub-sea acoustic sensor networks
Forward momentum
We now recognize how many applications can use Ethernet timestamps to do tasks more effectively. This is creating tremendous momentum to implement clock synchronization and packet timestamps throughout standard Ethernet networks.
As we resolve each technical challenge, it becomes easier to imagine new applications for Ethernet timestamps.
Alexandra Dopplinger, P.Eng., is Freescale Semiconductor's Global Industrial Segment Lead for Factory Automation and Drives. Her special interests include industrial network protocols, motor control and robotics. She graduated with B.Eng. (Electrical) from Memorial University of Newfoundland and holds a patent for a redundant LAN implementation.
Originally educated as an engineer, Bill Seitz has worked in the field of embedded systems for over 30 years specializing in field bus and data communication. Bill is currently the Managing Director of IXXAT for North America.
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