Electronic Design

USB 3.0 Protocol Analyzer Jumpstarts 4.8-Gbit/s I/O Projects

The USB 3.0 standard is almost upon us, and some of you are waiting to begin your new, faster I/O designs around it. Full ratification isn’t expected until later this year. When that happens, you’ll want to be the first in what appears to be some new markets for this ubiquitous I/O protocol.

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With its promised 4.8-Gbit/s speed, the standard will find its way into some products that heretofore weren’t USB territory, like external storage systems and consumer peripherals using video, photos, and music. The big issue for developers, though, is testing these USB 3.0 products.

It’s a complex protocol, and its 4.8-Gbit/s speed makes it a real challenge. Fortunately, LeCroy Corp. has foreseen your need and created the Voyager USB 3.0 validation system. It’s a protocol analyzer as well as a signal generator/exerciser that meets the most recent version of the 3.0 standard.

The USB interface was designed to replace older serial interfaces like RS-232 and even some parallel interfaces for use in connecting peripheral devices to personal computers. The architecture is basically a bus that can accommodate up to 127 nodes or peripheral devices of virtually any type. In its configuration, one host controller can handle the 127 nodes, usually through a hub.

The early version of USB came out in 1996 and offered a speed of 1.5 Mbits/s. A later update boosted that to 12 Mbits/s. An even faster version called High-Speed USB or version 2.0 boosted the data rate to 480 Mbits/s—that’s 60 Mbytes/s if you think in bytes, not bits. One cool feature of the USB port is that it is hot-pluggable. And, the USB cable carries the dc supply voltage of 5 V at a maximum current rating of 100 mA.

The newest version, known as USB 3.0 or SuperSpeed USB, promises 4.8 Gbits/s over a cable as long as 3 m. The technology is roughly based on the PCI Express Gen 2 specifications for 5-Gbit/s data transfers. It uses 8B10B encoding, linear feedback shift register (LFSR) data scrambling, spread spectrum, and clocking. It also uses lowfrequency periodic signaling (LFPS), dynamic equalization, and training sequences to ensure fast signal locking.

Otherwise, the standard is backwards-compatible with earlier generations of USB. Initial deployments aren’t expected until 2009, but it will definitely change the way we transfer the growing amount of data that business, industry, and consumers want to move.

A key part of the 3.0 version is a new connector and cable. It’s divided into two parts. The first part is the standard four-wire version with two unshielded twisted pair (UTP) data lines plus power and ground. The second part has five connections, including two additional UTPs, one for transmitting and one for receiving, devoted to the high-speed data transfer and a ground. The connector is backward-compatible with older sockets. An optical connector and cable may be available in the future.

LeCroy has announced a cool USB 3.0 test solution that is sure to simplify designs with this new standard. Called the Voyager USB Verification System, it is both a protocol analyzer and an exerciser (Fig. 1). The analyzer is designed to record and analyze USB 3.0 or 2.0 or both concurrently. It features a 1- or 4-Gbyte capture memory. You can get the product with just 2.0 capability with the option of adding the 3.0 test capability later. The product works with an external PC or laptop for processing and display.

To provide accurate data capture at 4.8 Gbits/s, the analyzer follows each link state transition and achieves bit lock in less than 1 µs. Any delay in signal lock causes the analyzer to miss date. The Voyager front end quickly recovers from the electrical idle state and shows all bus and power state transitions for the link under test.

The Voyager analyzer uses the de facto Computer Access Technology Corporation (CATC) Trace display to illustrate the USB 3.0 protocol, and it includes many enhancements to accelerate the testing of USB 3.0 links (Fig. 2). CATC Trace is analysis software used to decode, process, and analyze captured USB traffic. This feature digs deeply into the USB protocol and provides an intuitive and colorful display that highlights errors and problems.

Advanced triggering, hardware filtering, and Spec-View are all designed to help users quickly understand and verify early USB 3.0 protocol behavior. Spec-View software shows header packets in hex or binary. The new Link Tracker view shows raw 10-bit or hex symbols from upstream and downstream links time-aligned in a column format. This feature is invaluable in debugging SuperSpeed traffic, as it provides precise timing context for analyzing link power-management transitions.

Voyager also can detect and flag more than 40 link and protocol errors, including logical link and timing errors. At the lower layers, training sequiences and link commands are automatically verified for proper formatting. Spec-View displays header fields in hex or binary using a 32-bit table format, and it marks errors in red.

The exerciser generator can transmit both USB 2.0 and 3.0 packets, so users can emulate a host of device behaviors with low-level control of headers, payloads, link training, and timing. Also, the exerciser’s error injection and compliance verification lets early adopters get started. The Voyager has native USB connectors at the inputs on the analyzer and separate output connectors for the exerciser as well.

The front panel offers individual differential signal inputs and outputs for data and clock terminated at MMCX to SMA miniature coax connectors to provide access to the individual data and clock signals in testing. Trigger outputs are also provided. A USB host connector and 1-Gbit Ethernet connectors are included on the front panel.

If you’re looking for a way to speed up and simplify design and debug or USB 2.0 or 3.0 products, the Voyager may be a good place to start.

LeCroy www.lecroy.com

TAGS: LeCroy
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