PowerLink

2016-11-08T06:34:56Z

Introduction

After accumulating some experience with other Industrial Networks on FPGA, we converged on retaining only POWERLINK as well as our own Ultra-Low Latency Gigabit ring.

POWERLINK is a fast real-time field bus based on standard Ethernet. openPOWERLINK is an open-source implementation of this protocol, and comes with example designs targeting Intel (previously Altera) FPGAs.

Experience

Our experience with POWERLINK was very successful :

We quickly mastered the POWERLINK Slave Development Kit
We were able to build fully working slaves on very low cost FPGA boards (including the $25 BeMicroMax10 !)
The interaction with the openPOWERLINK maintainers was easy and productive.
B&R offers a serious support for Powerlink adopters.

Take a look at this presentation to find out more details about the systems we implemented.

Ultra Low Latency Network

2016-10-04T17:24:21Z

Introduction

Gigabit Ethernet over copper twisted pairs (1000BASE-T) is an ubiquitous, easy, and extremely reliable Physical Medium.
ALSE has developed a lot of experience around this technology, like the very innovative GEDEK communication kit (processor-less hardware stack) and allowed achieving reliably unprecedented data throughput. This technology has been used in hundreds of systems all over the world.

One of our clients expressed the need to build an architecture with up to more than 20 regulation and control boards interconnected together, and with a requirement that all boards should be updated with the regulation data from ALL OTHER boards during the first half of a single PWM cycle (targeted at 20 kHz). In other words, all the boards should see all the other board's data in no more than 25 micro-seconds.

Another requirement was the ability to implement redundancy.

Quite naturally Gigabit Ethernet comes to mind to implement the inter-boards communication.
However, even under underestimated conditions (20 slaves, 20 kHz, no redundancy), 40 Ethernet frames must circulate in much less than 25 µs. This simple calculation shows that a standard (store-forward) architecture, even with a near zero delay (like GEDEK) would be outperformed by a ratio greater than four !

Are existing solutions available ?

We conducted a careful pre-study and reached the conclusion that NO SOLUTION existed in the market that reached only a fraction of the performance required !

The table below, extracted from a very interesting article about Industrial Ethernet shows the state of the art.

[table]

Industrial Ethernet standards Cycle Time

Our solution

We use completely standard IEEE 802.3-2008 Ethernet frames.

We implement a “circular” bi-directional (dual) ring. Two frames circulate in opposite directions for a full turn, thus already implementing a first redundancy.

We use the Cut-Through Forwarding technology in our own optimized switch to reach an absolute minimal latency.

We use the Summation Frame method (each node adds it's own data in a slot of the circulating frame).

We use a fully Hardware implementation, thus removing any software interaction or limitation to the performance. In Hardware, decisions can be taken in less than 10 nanoseconds (ie practically at each incoming byte in the GbE link), with no jitter.

We re-used (and customized) our optimized and well proven Gigabit-only MAC (Media Access Control).

Note : We have implemented several clever optimizations to further reduce our cut-through switch latency. The details are only available after signing an NDA.

Network Topology

The figure below shows 9 boards connected together, one of which being the Master.

Network (ring) Topology

Test System

We have used 9 DE2-115 FPGA kits attached together mechanically to form a “tower”. See picture below. The DE2-115 (used in some Training courses) was available and it comes with two GBE interfaces (Marvell 88E1111 PHY).

This setup allows to practically measure with great precision the achieved latency in realistic conditions (including the delays in the Marvell Gigabit PHYs). The results were extremely close to our simulations.

Tower of DE2-115

Complementary tools

We have developed an “Embedded Sniffer” : a special version of the Master forwards all (or some) circulating frames to another (3^rd) Ethernet port for analysis with a PC using Wireshark, without disturbing the Ring network.

Conclusion

Our technology (based on an optimized ultra-low latency Gigabit Ethernet cut-through switch) can enable a new range of industrial applications that were not feasible so far.

If your system consists of several boards that need to communicate with each other and exchange data with very small delays and latency, our technology may help you. Do not hesitate to Contact us

A.L.S.E the FPGA Experts

PowerLink

Introduction

Experience

Ultra Low Latency Network

Introduction

Are existing solutions available ?

Our solution

Network Topology

Test System

Complementary tools

Conclusion