Mar 04, 2020 Dr. Design

TSN and Real-Time Operation from Wind River

By Andrei Kholodnyi, Janus Yau, Markus Carlstedt

Time-sensitive networking (TSN) is emerging in all market segments. It can provide the basis for real-time communication for an entirely new type of applications that could not exist before.

For example to decouple control functions from actuation and move those to the edge compute. Next generation automation controllers could process various workloads such as video stream and control traffic in parallel, calculate deep learning algorithms all in one machine, and simultaneously communicate with the other controllers on the factory floor in a timely manner. To guarantee a deterministic behavior in such environment a real-time operating system is needed on both ends.
For the applications that need both time sync (coordinated events) and timeliness (timely events) such as robotic arms, motion controllers or mobile vehicles, it is necessary to use TSN in a combination with VxWorks real-time operating system (RTOS) to synchronize networks of devices for improving the deterministic behavior. Combining TSN with real-time behavior of VxWorks operating system can enable customers to precisely control time-sensitive cycles.

TSN, a set of IEEE* standards, defines the protocols for the transmission of time-sensitive data over Ethernet. Real-time features on VxWorks, including hard real-time scheduler, real-time network stack can help to optimize the processing of data packets. TSN defines rules for time sync and timeliness to optimally transmit data between systems, whereas the VxWorks helps to design a distributed over deterministic network real-time control system.

Ultimately, TSN is an enabling technology to support the convergence of IT (Information Technology) and OT (Operational Technology) over cost effective standard non-proprietary Ethernet network that drives higher productivity and reduction in cost across many industrial use cases. The key to its successful adoption is interoperability.

LNI 4.0 TSN Testbed Plugfest
Wind River recently participated in a TSN Testbed event. At the plugfest Wind River connected two different boards to the TSN network. Both boards were running an early version of the next VxWorks release (SR0640) which includes support for several TSN standards; 802.1AS, 802.1Qbv and 802.1Qbu. The first board was a NXP LS1028ARDB reference platform and the other was an Intel UP2 board with i210 NICs.

The first test in the LNI 4.0 TSN testbed was to verify that the VxWorks implementation of Precision Time Protocol (IEEE1588) was compatible with other devices implementations. At the plugfest the 802.1AS profile was used predominantly. The testing showed that the VxWorks devices interoperate correctly with all other devices that were connected. The VxWorks clock synchronized quickly and the offset to the master clock kept below a few tens of nanoseconds for a direct connection.

Two different boards were used for testing: NXP LS1028ARDB and Intel UP2 with two i210 interfaces

Secondly, the VxWorks devices were configured to transmit packets to the TSN network according to the format defined by the LNI 4.0 TSN testbed talker application. This application transmits Ethernet packets periodically at defined offset into a test cycle running at 1000 microseconds. According to the 802.1Qbv standard, packets can only be transmitted at pre-defined time slots in the cycle in order to guarantee delivery at the receiver. The testing showed that the VxWorks devices successfully transmitted packets with the specified periodicity and with low jitter. In a five-minute test, transmitting 1000 packets per second, all packets reached the receiver at most 40 nanoseconds outside of its nominal time with a jitter of 10 nanoseconds.

LNI 4.0 TSN plugfest group photo. It was such a great opportunity not only for the TSN testing itself but also for networking! Thanks to Dominik Rohrmus and Frank Schuberth for organizing this event

Wind River Alignment with TSN Standards
Wind River is committed and taking a pragmatic approach to enable TSN, working with our hardware partners to leverage the deterministic real-time performance of VxWorks to maximize the TSN hardware capability. Latest VxWorks includes the technology to implement TSN features defined by the following standards across number of TSN capable hardware:
• IEEE standard 802.1AS - a timing and clock synchronization protocol standard that allows all participating devices in TSN network are synchronized to a global time in high precision within nanoseconds. It forms the foundation for the scheduling of traffic queues through each participating network devices.
• IEEE standard 802.1Qbv – a scheduling protocol standard that makes use of multiple queues to queue up device transmitting data, and combines with time gated scheduling control to ensure data transmission delays can be managed deterministically. This allows for the convergence of critical and non-critical data traffic on the same network.

VxWorks are also investing to advance TSN on other areas:
• IEEE standard 802.1Qbu – an enhancement to 802.1Qbv that prevents large non-critical data from using up the network bandwidth and allows critical data to break up the non-critical data to achieve minimal communication delay and optimal bandwidth usage.
• Simplifying Configuration and deployment – looking at opportunities to reduce complexity of TSN configuration, allow ease of debugging, optimization & deployment. Find best ways to interoperate VxWorks in centralized vs distributed TSN network environment.

Wind River is also committed in taking part in industrial consortium and events, working with multiple partners, vendors and customers to ensure maximum interoperability for the markets.

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