High-speed serial links are here to stay

January 04, 2013

Bernard Cole-January 04, 2013

There was a time, not more than a decade ago, when parallel buses were king and they were the primary means of moving information between systems, within systems and boards and between components on a printed circuit board in a design.

Now, high speed serial interconnects are dominant in almost every embedded systems design, from consumer and mobile devices to the high end routers and switches that power the wired Internet backbone.

The range of designs that an embedded systems developer must be sure have reliable and high quality signal integrity over such interconnections range from car rear-view camera systems, where the data rate is usually less than 1 Gbps to high-bandwidth Internet optical routers, where data rates are 10Gbps or more.

Fortunately – or unfortunately depending on how you look at the problem - there are a number of different serial interconnect topologies and standard to help you, including SuperSpeed USB (Universal Serial Bus) 3.0, PCIe (Peripheral Component Interconnect Express), XAUI (10-Gbit attachment-unit interface), InfiniBand, RapidIO, and SATA (serial advanced-technology attachment) transmit data and clock signals using differential signals. And common to them all is the ubiquitous and ever useful serializer/deserializer (SERDES) interface that converts data signals back and forth between serial and parallel form.

A commonality amongst such protocols is that the data transmitted embeds the clock, and the receiving system often uses 8b/10b encoding to provide a means of reliable clock extraction. Multilane implementations of these technologies bring further complexities. Four, eight, or more serial lanes carry signal components from transmitters to receivers, all with the goal of higher data throughput.

In such topologies it can become a considerable challenge to hunt down and find even such mundane problems as a clock that intermittently outputs an incorrect duty cycle or a rise time that occasionally fails specifications.

Adding to the challenge of ensuring signal integrity is that many of these complex high-speed serial buses use a variety of CDR (clock-data-recovery) techniques for data transmission or specialized 8b/10b encoding schemes. Adding to the complexity of the problem is the trend toward multilane serial configurations.

Facing such ongoing challenges in such designs requires that embedded developers continually educate themselves in all of the techniques and methodologies available. A good first step is to rely on web site resources such as Embedded.com where we are constantly adding to a knowledge base that has taken us a decade or more to create on the various serial design techniques available.

These resources come in the form of design articles, technical papers and webinars, complemented with a range of relevant news and product stories. Some of the most recent of these are highlighted in the Embedded.com Tech Focus newsletter this week: "Building reliable high-speed interconnects."

To save you the hassle of searching the site with Google or our own internal search engine, a good second step is to make use of our Collections Archive, in which we have gathered many of the articles on serial protocols into a single collection.  Of these many resources, some of my Editor’s Top Picks include:

Verifying serial buses and components in embedded designs
Debugging common serial buses efficiently
Multiband architecture for high-speed SerDes.
Signal integrity analysis techniques for high speed serial links.
Using PCI Express as a fabric for interconnect clustering
Rapid- and full-speed USB .3.0 development on Cortex-M MCUs

A third and final step is attendance at the 2013 DesignCon January 28 to 31 in Santa Clara at which there will be a three-day track of classes devoted to high speed serial interconnect design.

Because high speed serial interconnects will be with us for a long time, the goal on Embedded.com is to continue to provide the most relevant design information available. For that we require your participation as well, in the form of blogs and design articles on serial interconnect design that you submit as well as your suggestions about the kind of content that would be most useful to you. I look forward to hearing from you.

Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. He welcomes your feedback. Send an email to bccole@acm.org, or call 928-525-9087.

See more articles and column like this one on Embedded.com. Sign up for the Embedded.com newsletters. Copyright © 2013 UBM--All rights reserved.

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