Networking and Fieldbus
In the IoT era, embedded systems no longer standalone but rather are required to interconnect and share messages deterministically so that the system of controllers can be optimized. IntervalZero has four different real-time networking solutions that are application-dependent.
- TCP stack for use with the real-time subsystem
- Network Abstraction Layer (NAL)
- Time Sensitive Networks (TSN)
Non-Deterministic Network Application Interface
- Virtual Network (VN)
Network Abstraction Layer (NAL)
The NAL was created to provide engineers with access to modern Ethernet adapter features that are not available through the traditional TCP/IP stack interface. For example, the Intel i210 includes support for Layer 2 protocols, such as IEEE 802.1AS (Time Synchronization) and 802.1Qav (Audio-Video Bridging), as well as hardware support for IEEE 802.1Qat (Stream Reservation Protocol) and IEEE 1588/802.1AS (time stamping). Lead edge adapters also support multiple priority queues which isolate time-sensitive traffic from other traffic at the hardware layer.
TCP Stack for the Real-time Subsystem
The TCP/IP stack for use with the real-time subsystem (RT-TCP/IP) is a separately purchasable feature of RTX64. RT-TCP/IP allows real-time processes to use standard socket API calls for communication. RT-TCP/IP is a deterministic stack based on the Treck Inc., Treck TCP/IP stack, a high-performance TCP/IP protocol suite that is RFC compliant.
The Virtual Network add-on simplifies the integration of the RTX64 real-time processes with an HMI or a Windows process by delivering a point-to-point connection between Windows and RTX64 that emulates a TCP-based local area network connection on a system. This integration simplifies the user experience while providing more versatile options for how an application can be configured.
Fieldbus is an industrial network system for real-time distributed control. In an automation context, a machine controller needs to integrate sensors, actuators, electric motors, console lights, switches, valves, and contactors. In a machine context, traditionally, manufacturers sponsored fieldbus development to support their hardware and examples include Modbus, PROFIBUS, CAN, DeviceNet, Mecharalink, ccLink, and many others. Recently, several digital open standards have evolved that support the use of the CAT 5 Ethernet cable including EtherCAT, Sercos, ProfiNET, Powerlink, and more. EtherCAT has emerged as the de-facto standard. In any event, RTX64 relies on partners to deliver the real-time driver to allow RTX64 applications to deterministically connect to a field bus.
Standard IT network equipment has no concept of “time” and cannot provide synchronization and precision timing. Delivering data reliably is more important than delivering within a specific time, so there are no constraints on delay or synchronization precision. Even if the average hop delay is very low, individual delays can be unacceptably high in a deterministic setting. Time-Sensitive Networking (TSN) is a standard that supports hard real-time communications based on a switch network. This differs from a Fieldbus approach which does not support switched networks. IntervalZero has partners that support this model and also has the ability for customers to build their own with RTX64.