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Pi HAT brings Time-Sensitive Networking (TSN) to Raspberry Pi 4

Aug 18, 2021 — by Jeff Child — 898 views

InnoRoute has launched its “Real-Time HAT” for the Raspberry Pi 4 with support for TSN and other real-time protocols. The Artix-7 FPGA-based HAT supports TSN and PoE through its 3 GbE ports.

InnoRoute has rolled out the Real-Time HAT, a HAT that brings Time-Sensitive Networking (TSN) capability to the Raspberry Pi 4. At the heart of the Real-Time HAT’s functionality is a Xilinx Artix-7 FPGA and three Analog Devices ADIN13007 Gbit Ethernet transceiver PHY chips. The HAT enables precise network timing for real time protocols such as TSN and others. It can do synchronization between HATs, over the network, or with external GPS PPS. Its connectors are set up so that additional HATs can be stacked on top.

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Real-Time HAT (left) and Real-Time HAT on a Raspberry PI 4B
(click images to enlarge)

InnoRoute says it created Real-Time HAT as a low-cost alternative to it high-end industrial Ethernet/TSN router, TrustNode. The company also saw a need for a general-purpose FPGA HAT with Ethernet ports, for network monitoring on a Raspberry PI, and for hardware-accelerated routing and other applications. The Raspberry Pi’s Ethernet connection lacks features useful for many professional networking applications, like time-triggered sending of frames, precise reception timestamping for advanced traffic analysis, and precise and accurate network time synchronization, says the company. Meanwhile, the RPi cannot easily be used in between other network devices, because it provides just one network port. The Real-Time HAT solves these issues, while adding other network-related features.

We’ve covered a steady stream of Raspberry Pi HAT products so far in 2021, including Blinkinlabs’ JTAG HAT, Seeed’s WM1302 HAT with LoRaWAN Gateway Module, Zymbit’s HSM4 security module HAT, and Raspberry Pi Trading’s own PoE+ HAT. This is the first HAT we’ve seen with TSN, although we’ve seen TSN offered on other module and box products such as TQ Embedded’s TQMa65xx module, Vecow’s rSPC-6000 embedded PC, and Adlink’s LEC-iMX8M SMARC module. The Adlink product offers IEEE-1588 compliant PTP (Precision Time Protocol) and optional TSN support.

As shown in the diagram below, the Real-Time HAT has a Xilinx Artik-7 FPGA and two memory chips for optional buffer extension. For networking, GbE port 0 provides IEEE1588/TSN signaling. GbE port 1 links to the Raspberry Pi 4 and GbE port 2 enables PoE without TSN. The board has a standard 40-pin Raspberry Pi header. Other components include JTAG and PMod connectors, 3x LEDs, and an EEPROM for Raspberry Pi HAT compliance.

Real-Time HAT components
(click image to enlarge)

The Real-Time HAT links with the Raspberry PI through two interfaces, as shown in diagram below. Packet transfer is done via a short Gbit Ethernet link, while the Raspberry PI’s GPIO header is used for configuration and status signaling. For throughput, the HAT provides line-rate forwarding at the selected speed (10/100/1000 Mbps per port). Forwarding is limited only by the Raspberry Pi’s GbE interface. For the Raspberry Pi 3B+ and below, throughput is limited by the USB network interface of the Pi mainboard. However, the HAT supports Gbit line-speed, which is important for time-triggered transmission, says InnoRoute.

Interconnect between Raspberry PI and Real-Time HAT in the TSN bridge to standard Ethernet
(click image to enlarge)

TSN technology is used in industrial control applications, automotive control, professional audio/video processing, aerospace/defense on-board networks, and telecommunication/5G networks. These networks consist of TSN switches and TSN endpoints. InnoRoute says a Raspberry Pi with a Real-Time HAT can be used as a TSN endpoint — even a switched TSN endpoint (line topology). The Real-Time HAT is based on InnoRoute’s TrustNode system, a software-defined networking (SDN)/TSN switch.

The company describes several use cases for the HAT: (1) As a Linux-TSN Raspberry Pi endpoint with high precision to inject precisely scheduled Ethernet traffic in a TSN Network; (2) To connect non-deterministic Ethernet services to real-time networks; (3) For time-accurate network device testing; and (4) As an FPGA-based network TAP (test access point). As is pointed out in the Hackaday story that brought this news to our attention, the nuclear research center CERN makes very heavy use of precision time protocols like IEEE1588 for its huge arrays of sensors and control equipment that enable all its LHC experiments.

For the TSN features, InnoRoute provides patches to the network driver of the Raspberry Pi 4. However, for the Raspberry PI 3 the same changes need to be applied. As a result, InnoRoute started with the Raspberry Pi 4 and plans to support the Raspberry Pi 3 at a later time. Meanwhile, users can use the code from its github repository and adapt it to other platforms.

Further Information

Although no pricing is available, InnoRoute is taking pre-orders now for the Real-time HAT, as well as a variant called the Real-Time HAT Automotive. Those pre-orders can be made from the Real-Time HAT’s product page.

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