USB

Standards Drive USB Evolution

Ellen Konieczny

Specifications like SuperSpeed USB 3.0 and StackableUSB are being spawned to allow USB technology to fulfill high-speed, rugged, and even wireless applications outside of the PC space.

According to In-Stat, Universal Serial Bus (USB) is the most successful interface in existence. In 2008 alone, over three billion USB devices shipped. USB has been broadly adopted across PCs, PC peripherals, consumer electronics, communications, and automotive devices. Now, the industry is looking to broaden this technology’s reach through standards efforts. USB 3.0—also known as SuperSpeed USB—promises to deliver power efficiency together with speed of 5 Gbits/s—a tenfold improvement over Hi-Speed USB or USB 2.0. At the same time, StackableUSB has emerged to enable USB to be used in more rugged applications. Going forward, these and other specifications will enable USB to support new applications.

According to a recent report from In-Stat (www.in-stat.com) titled, “Wired USB 2009: High-Speed Rules, SuperSpeed On The Way,” the global recession will prompt a slight decline in USB-enabled device shipments this year. Over the next several years, however, USB 3.0 will fuel that market. In-Stat forecasts that SuperSpeed USB will represent over 25% of the USB market by 2013. For PC peripherals, however, the speed of that success depends on how quickly USB 3.0 is integrated into these devices’ application-specific integrated circuits (ASICs) and microcontrollers.

External storage devices are expected to be the first to adopt the SuperSpeed USB standard, due to the excessive time that it takes to currently download or backup large media files over legacy USB or FireWire interfaces. For example, it would take almost 14 hrs. to transfer the contents of a 1-Terabyte drive over USB 2.0 compared to just 1.3 hrs. with USB 3.0. According to Mike Micheletti, LeCroy’s (www.lecroy.com) product marketing manager, “The introduction of USB 3.0 is specifically targeted at storage applications and will feature an enhanced massstorage architecture called USB Attached SCSI (UAS) protocol. This enhanced protocol will allow USB device controllers to implement data streaming and command queuing for improved I/O efficiency. Taking advantage of this new capability will require new drivers for both the host and embedded device stack. While these are generally provided by the I/O or operating-system (OS) software vendor, there will be additional testing needed by USB application developers.”

To support the evolution to USB 3.0, LeCroy already has a number of test options available. Recently, Symwave (www.symwave.com) utilized LeCroy’s Voyager M3 USB host emulation platform for system design validation and specification compliance of its SuperSpeed USB 3.0 to SATA storage device. The LeCroy Voyager M3 USB protocol analyzer with integrated exerciser was used to emulate a USB To support the evolution to USB 3.0, LeCroy already has a number of test options available. Recently, Symwave (www.symwave.com) utilized LeCroy’s Voyager M3 USB host emulation platform for system design validation and specification compliance of its SuperSpeed USB 3.0 to SATA storage device. The LeCroy Voyager M3 USB protocol analyzer with integrated exerciser was used to emulate a USB 3.0 host controller, generate USB 3.0 traffic, and monitor end-to-end data transfers to the Symwave USB 3.0 device controller (see Figure 1). The company’s ReadyLink feature provides full-function link-layer emulation that automates all link-layer handshaking, training, and flow control.

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Figure 1: To accurately capture data at 5 GHz, this analyzer must follow each link state transition and achieve bit lock in under 1 μs when moving from idle to the active state. Any delay in signal lock can cause the analyzer to miss data.

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Figure 2: Shown here is a StackableUSB quarter-size stack. Compared to the 104 form factor, the quarter- and half-size StackableUSB I/O boards better match the space needed to implement simple I/O onto stackable boards.

Although it plans to support USB 3.0 as it evolves, the StackableUSB specification focuses on ruggedness rather than speed. Specifically, it ruggedizes USB into compact form factors to enable the technology to move into harsh environments like military and industrial-control systems. By using USB 2.0 connectors, StackableUSB mates central processing units (CPUs) and I/O boards to eliminate cables, reduce pin count, and provide a smaller connector footprint than traditional interconnect architectures (see Figure 2).

According to Susan Wooley, StackableUSB’s chairperson of the board, “StackableUSB electrically supports five USB root ports on the top side and five on the bottom side of a single-board computer as well as I2C and SPI. The number of USB root ports available to the user is determined by the number of USB ports supported by the single-board computer. Additionally, each USB port provided by the processor can be expanded using a hub interface to provide for an additional four to seven devices.”

Wooley adds, “To ensure mechanical compatibility, StackableUSB defines a new physical form factor to implement smaller, embeddable USB I/O—one that scales down the older, traditional I/O boards to one-fourth the size of previous generations. These smaller, yet more powerful device-side I/O boards measure 1-7/8 x 1-7/8 in. and can be added to a system in a variety of ways. Depending on one’s space constraints and system design, the boards can be stacked together to form a rugged, standalone, brick-like unit. They can be added to a carrier board accommodating up to four StackableUSB devices on any single-board computer. Or each device can be attached to the processor unit via a standard USB connector and cable.”

Despite the obvious benefits of StackableUSB, embedded developers have been frustrated by the inability to easily attach or interface StackableUSB off-the-shelf control products into their systems. To eliminate this problem, Micro/sys (www.embeddedsys.com) recently debuted the USB4364, USB5364, and USB3364 carrier boards. They support, respectively, the Nano-ITX, Pico-ITX, and 104 form factors while giving OEMs a direct connection from their processor board’s PCstyle USB ports to StackableUSB clients. The carrier board, which utilizes the Nano-ITX, Pico-ITX, or 104 form-factor mounting holes, attaches to the single-board computer and creates up to four USB bays per carrier board.

Aside from efforts to have USB serve as a peripheral connection in markets outside of the PC segment, USB development is being driven by an increasing demand for wireless connectivity. According to Bill De Vries, Icron’s product marketing manager, Icron already has products that deliver USB over standard IEEE 802.11g radios. The firm is working on delivering USB connectivity over additional media. De Vries notes, “Finding ways to remove the demand for more wires in the system will be a challenge. Certified Wireless USB was a start, but it hasn’t been proven that the Ultra Wideband (UWB) radio technology is up to the challenge. Established radio solutions, such as IEEE 802.11n, are a natural fit. In addition, providing simple wireless USB connections for the industrial/commercial space along with the consumer space appears to be very lucrative but also a large technical challenge.”

Even if firms are still using legacy, non-USB peripherals, they can begin moving to USB with the help of companies like Future Technology Devices International Ltd. (www.ftdichip.com), which converts such peripherals to USB. The time to transition to USB is now, as emerging standards are enabling the technology to bring its ease of use and plug-and-play advantages to new, exciting markets. For example, Bill De Vries points to the convergence of the PC and TV, which will likely lead to TVs of the future being able to simultaneously operate as PCs. Icron is currently working on a version of the PC-on-TV over Wireless- N, which offers full USB compatibility with all of the USB devices on the market. Innovative homeconnectivity applications like these will be among the drivers that increase the demand for USB-enabled devices in the future.

Ellen Konieczny is a freelance writer who has extensive experience creating manuals and other technical documents for companies. She can be reached at ellen.konieczny@gmail.com.