RTC Magazine

Advances in computer technology often seem like a game of juggling bottlenecks. If processor performance seems too slow, the industry comes out with higher-speed CPUs. Then, of course, operating systems and applications see the increased potential and add features, which demand more memory. Then transferring data becomes a hurdle and we get advances in interconnects. These steps are accompanied by tons of white papers, market studies and oceans of PowerPoint slides—but inexorably the world advances.

These periods of intense activity, innovation and hype are usually interspersed with intervals that can informally be referred to as “shake-out” times. That is, when a number of competing approaches have been put forward, engineers, marketers, users and OEMs evaluate, use, experiment, improve and ultimately adopt or reject them. We appear to be in such a period in terms of interconnects.

Remember back several years ago when serial switched fabrics hit the scene? Initially there were over 100 of them thrown up against the wall. Think back now and see if you can name six of them (cue the Jeopardy music). Well, don’t feel bad—you’re only going to need to remember three interconnect technologies for the foreseeable future: Ethernet, PCI Express and USB. The rest are falling by the wayside or crawling into niches to eke out a limited existence.

Ethernet should come as no surprise. It has been ubiquitous for many years, dominates both wired and wireless LANs and connects us all to the Internet. TCP/IP now takes us—via IPv6—from the Web all the way to individual sensors and actuators. Practically every CPU board sold today has at least one Ethernet connection and these are commonly offered as 10, 100 or 1000 Mbit/s speeds. 10 Gigabit Ethernet is now becoming more widespread and higher speeds are in the future. Ethernet connectivity enables embedded Web servers to provide remote monitoring and control of devices large and small and in large numbers. Ethernet is here to stay.

A less obvious but nonetheless solid victory is being achieved by PCI Express (PCIe). At first it seemed an “also ran” among such competitors as Star Fabric, HyperTransport, RapidIO and InfiniBand See? I named four! Its hidden advantage, however, was backward compatibility with the PC-based PCI interconnect and the attendant economies of scale that come with the PC market. Gen2 PCIe is about to break into the world with 5 Gbit/s speeds per lane, and 10 Gbit/s Gen 3 will eventually follow.

It was once a truism to think that PCIe was fine as an interconnect between components and boards “inside the box,” but to go between chassis you needed a different interconnect, most prominently InfiniBand. Now, however, that is changing. PCI Express over cable, pioneered by One Stop Systems, lets systems communicate up to seven meters between chassis. In addition, I/O and clustering using PCIe switches being introduced by Dolphin will enable fiber-optic connections of at least 300 meters between nodes. Not only that, One Stop’s SuperSwitch technology will enable PC-to-PC networking via nontransparent bridging between CPUs on a backplane or among boxes. Why, then, would anyone use InfiniBand when an all-PCIe solution is at hand?

And then there’s USB. USB 2.0 is already finding its way into the embedded space, most recently in the form of Stackable USB developed by PC/104 maker Micro/sys. But it is showing up in other forms as well, driven, again, by economies of scale, low-cost components and software compatibility. Now, Intel, HP, TI and other companies have formed a group to promote USB 3.0, which will have speeds approaching 5 Gbits/s and will significantly reduce power consumption, yet be backward compatible with previous USB specs. Add to this the just-beginning deployment of Certified Wireless USB, and the potential for low-cost, high-speed peripherals, both wired and handheld, takes a quantum leap.

These developments in the world of interconnects also fuel the trend toward the use of small form-factor boards, which are primarily PC-based. This means that most of them incorporate PCIs as well as Ethernet as a matter of course. USB can and will be included as needed, but will perhaps not be as universal. The pervasive growth of embedded PC-compatible small modules can be expected to make the “magic three” interconnect technologies even more common.