PCI Express, the new high-speed version of the venerable PCI personal computer bus, is coming on line in the embedded systems world as it makes inroads in PCs. At the same time, a pair of competing high-speed architectures, Infiniband and Rapid IO, are beginning to see acceptance and noticeable effects in some embedded applications.
The three architectures are expected to make a solid impact in the market this year as silicon becomes more readily available and prices drop. Design engineers will often be able to eliminate bridges by switching to these switched fabric interconnects, simplifying designs in addition to upgrading performance. Implementation in the many fields of the embedded world is likely to vary widely as vendors pick various traits for specific applications.
PCI Express is expected to have solid usage inside system boxes, using serial communications to give engineers up to 8.5 Gbyte/sec in applications that are now getting less than 1 Gbyte/sec with the conventional PCI bus. Though its transmission distances going outside the box are limited compared to Infiniband and Rapid IO, PCI Express will give users the economies of scale linked to the huge volumes of the PC world. "There are dozens of companies coming out with silicon, and all the components for Ethernet, SCSI and other technologies will be compatible" says Larry Chisvin, marketing vice president at PLX Technology, (www.plxtech.com/products/pci_express/default.asp) a Sunnyvale, CA chipmaker in that group.
Infiniband and Rapid IO will often be used to complement PCI Express, providing internal links and connections to external devices. The diverse nature of embedded applications leaves room for plenty of interpretation on where the buses can be deployed. "We don't see Infiniband as an embedded link, but we like it as a link between boxes," says Rich Jaenicke, director of product management at Mercury Computer Systems Inc. (www.mc.com).
A key aspect of success for these architectures will be chip support. Right now, Rapid IO seems to be in second place in that regard, following PCI Express. "Rapid IO has been adopted by many DSP vendors. They're putting the interface in the corner of FPGAs and using it on special processors for security, communications, and other fields," Jaenicke says.
Time-to-market will also play a role in bus selection. PCI Express chips are just beginning to roll out, and Rapid IO systems and chips are available but still somewhat limited. "Infiniband is the only technology widely available today," says Ronnie Sanford, marketing manager at Vmetro Inc. (www.vmetro.com). However, many companies including Vmetro often support more than one bus architecture, giving design engineers more options.
Picking an architecture is something engineers can leave until late in the design process. These serial communication links are often housed on mezzanine cards that plug into the motherboard, making it easy to change the communication architecture.
Comparing Buses: A hierachy of buses, including emerging architectures like PCI Express, address needs for communicating inside a system box and for larger systems that msut link several boxes together.