USB Learning Curve Gets a Little Steeper, But Resources Are Out There



Whether you need expert opinion on a schematic, feedback from a certification workshop or want to know more about cryptographic authentication, help isn’t just on the way, it’s here.

Figure 1: (Courtesy Microchip)

Figure 1: (Courtesy Microchip)

For this month’s Round Table Chuck Trefts Director, North American Ops Mobile for Ellisys, Mick Posner, Director of Product Marketing, USB & DisplayPort IP Solutions, Synopsys, and Mark Gordon, Senior Product Marketing Manager for Microchip’s USB and Networking Group, respond to our questions on USB Type-C, USB Power Delivery, and USB 3.1.

EECatalog: What are some hurdles USB adopters must overcome to enable users to take full advantage of USB 3.1 high performance?

headshot_webMark Gordon, Microchip Technology: Signal integrity is probably the biggest concern to USB adopters as they design boards and systems around USB technology. Most Microchip USB and Networking products contain a mix of sensitive analog circuitry, digital core logic, and high speed I/O circuitry. The PCB’s design can either enhance or detract from desired operation. Microchip provides design and layout guidelines (AN26.2) that help with development, but it’s our USBCheck™ services that enable our customers to get to first time success with their specific PCBs. USBCheck allows customers to send in their schematic or layout to Microchip for review prior to execution of PCB manufacturing. By reviewing hundreds and hundreds of designs, the Microchip team provides valuable feedback within 48 hours of receipt.

headshot3_webChuck Trefts, Ellisys: USB 3.1 doubles the link speed to 10 Gbps, so the hurdles are going to relate to the design and testing relative to the lower layers of the specification, specifically the physical and link layers, although there are also significant changes in the protocol layer. Changes also involve the encoding scheme, with the change from 8b/10b encoding to 128b/132b encoding and major changes to the low frequency periodic signaling, now more elaborate due to speed negotiations for connecting a 5-gigabit product to a 10-gigabit product.

To help manage all of this we provide a single hardware/software solution, our USB Explorer 350. It characterizes various USB technologies (including USB 3.1, Type-C, USB Power Delivery and alternate modes) in different ways, including thorough protocol analysis and compliance testing that is sanctioned by the USB-IF and used in USB-IF certification workshops, which take place more or less quarterly. Independent test labs also use this product for certifications outside of the quarterly USB-IF cycles.

Our USB Explorer tools are also used for traffic generation and eye pattern analysis. The eye pattern analysis characterizes the communications scheme for USB Power Delivery at the physical layer; link layer test and analysis, Type-C state machine test and analysis, and all kinds of engineering toys that help bring the latest generation of USB products to market.

headshot2_webMick Posner, Synopsys:
USB 3.1 Gen2 enables 10Gbps data transfers to/from an Application Specific Integrated Circuits (ASIC) or system-on-chip (SoC) to the outside world. The complete design including the hardware (HW) and software (SW) stacks must be optimized for throughput to achieve this goal. Synopsys’ complete DesignWare® USB 3.1 solution consisting of digital controllers, PHYs, verification IP, IP subsystems and IP prototyping kits enable a designer to quickly integrate, validate and accelerate software development for this latest USB standard. In addition, an important challenge typically overlooked is printed circuit board (PCB) routing, which is critical for meeting the USB 3.1 10Gbps tight channel budget. To address this, Synopsys provides models to help designers simulate package and PCB effects, ensuring first time success. By providing a complete, certified solution (Figure 2) for all aspects of a USB 3.1 design, Synopsys enables designers to quickly implement USB 3.1 functionality into their SoC and achieve the maximum USB system throughput.

Figure 2: Synopsys’ Complete USB IP Solution

Figure 2: Synopsys’ Complete USB IP Solution

EECatalog: Are there potential USB 3.1 pitfalls to avoid?

Chuck Trefts, Ellisys: With Type-C and USB power delivery added to the USB mix, there are a steadily increasing number of developers that are new to USB in general. Even some fairly big companies have not had a presence in USB, and they need to learn a whole new set of tools and testing.

With Type-C, USB opens up a communication channel to other communications standards, so we are no longer strictly USB. In an alternate mode environment for USB Type-C, we use the Power Delivery protocol to negotiate what we are going to exchange over the gigabit lane, and that might not be USB. It might very well be, for example, Thunderbolt or DisplayPort. Opening up to communications standards other than just USB invites all kinds of new companies into the mix.

And for these new entrants there is a learning curve. They need to know what kind of tools are out there, which tools are approved, and the difference in test coverage from one tool to the other. As well, they need to understand how the test process works, how the qualification process works, and waiver procedures.

My advice to any USB developer, especially newer entrants, would be to take their time making decisions on which tools are needed and which are not, and understand the overlap between the different tools. Understand which free tools and testing resources are out there, including those available from USB-IF. Also, make sure they are checking with unbiased sources such as USB-IF for information on how compliance testing works.

I also recommend companies prepare their budgets well in advance. The competition out there is very fierce among an expanding base of developers, and I do see more and more of these developers who cannot get products certified by USB-IF despite many attempts to do so, because they don’t test in advance, they don’t test during development at every stage, or they use the wrong tools or incomplete tools.

Mick Posner, Synopsys:
Yes, there are some potential pitfalls but the biggest by far is interoperability. USB 3.1 must interoperate with USB 3.1 Gen 1 (aka USB 3.0) and USB 2.0 devices, meaning hundreds, possibly thousands of interoperability tests are needed. Using IP that has been extensively tested and certified is vital to reducing integration risk and speeding time to market. Synopsys developed early USB 3.1 prototypes and has conducted extensive interoperability testing with other USB designs and products. Synopsys is the first and so far the only IP company to achieve USB 3.1 IP certification from the USB Implementers Forum (USB-IF). To attain certification, Synopsys USB 3.1 controllers and PHYs had to pass all the USB-IF protocol, electrical and interoperability tests for USB 3.1 Gen2, USB 3.1 Gen1, and USB 2.0. Having certification enables designers to have confidence that their products will meet USB-IF criteria and ensures interoperability.

Mark Gordon, Microchip Technology: At 10 Gbps, the new USB 3.1 Gen2 will pose design problems not seen in early versions of USB. One issue in particular will be the recommended cable distance between ports. The 2.0 specification limits the length of a cable between USB 2.0 devices (Full Speed or Hi-Speed) to 5 meters (or about 16 feet and 5 inches).

The 3.0/3.1 specification does not specify a maximum cable length, but there is a recommended length of 3 meters (or about 9 feet and 10 inches). For the new USB 3.1 Gen2, maximum cable length without having an active cable is recommended at 1 meter. This poses a problem for high data rate transfer applications like SSD and high-end cameras. 10 Gbps designs will have very little room for error, requiring very high signal-to-noise ratios to ensure quality signals over 1 meter, putting further emphasis on implementation quality and reliability. Companies, like Microchip, with a long standing history in the USB 3 market are in the best position to ensure the quality needed to meet the requirements of next-generation USB products.

EECatalog: What power distribution, connectivity and security trends are you keeping an eye on and why?

Mick Posner, Synopsys: Synopsys has been an active participant in many of the USB-IF specification groups for more than a decade, so we not only track the trends, we help drive the standard specifications for them. With the new reversible USB Type-C connector comes data, power and audio/video capabilities for almost every type of product. USB products that need these advanced capabilities will benefit from higher charge current, allowing faster charging without complex and/or proprietary circuitry. Security is indeed a ‘hot potato’ as we move towards an ‘everything connected’ society. Snooping of private data, side channel attacks, malware, data breaches and theft are some of the vulnerabilities that we must protect against. Synopsys’ portfolio of Security IP and Software Integrity solutions is uniquely aligned to address these security concerns.

Mark Gordon, Microchip Technology: The new USB-IF Power Delivery specification will change the face of USB over the next five years. We saw this when Battery Charging was released in 2010. Now, almost all portable devices use USB for charging. Power Delivery will be adopted the same way, but now instead of only providing up to 7.5W of power, USB is now poised to provide up to 100W.

Even more important than Power Delivery is the industry’s adoption of the USB Type-C connector. It will completely change the way host systems and devices interface together over time. The interface is smaller, symmetrical, bi-directional and will ultimately be cheaper than the Type A/B connectors presently deployed.

Additionally, the adoption of authentication methodology as part of the USB Type-C spec will initially be used to protect against non-compliant USB chargers, but ultimately it provides a methodology for enabling crypto based authentication right at the USB interface, prior to any data (or power) being provided.

As a USB silicon provider, simplifying the electrical interface around USB Type-C to enable high-speed data along with power and authentication functionality is our #1 goal as a company.

Chuck Trefts, Ellisys: USB Power Delivery and Type-C are expanding the footprint of USB functionality enormously, and they are keeping us quite busy because some of those specs are still moving. We are a very long term USB company, since 2000. So anything USB-related we will watch and likely support—not everything! There have been a couple of attempts out there on the part of USB-IF that didn’t quite fly, or just had sort of a minimal trajectory, but in general most of the things the USB folks attempt are successful. USB Type-C and USB Power Delivery are absolutely spot on and resonate with what’s needed out there.

The cryptographic authentication protocol that many Type-C products, such as chargers, cables, power sources and other various devices, are implementing will help assure that uncertified or otherwise undesirable devices are not allowed to work together at the cable level and the power level.

As soon as two USB devices are attached, the host system can use this protocol as defined in the spec to do some checks of the two devices to make sure the device is certified by the USB-IF. The host device can make decisions about whether to allow transfer of data or whether to limit power.

This goes to safety and security. On security for example, a company could implement a policy on employees’ computers that would disallow connections of non-approved storage devices.

EECatalog: What USB issues may not be getting the attention they deserve and why do we need to pay more attention?

Chuck Trefts, Ellisys: One thing that concerns a lot of folks in our business in general is the coming wave of these uncertified USB products, especially Power Delivery and Type-C products. We are starting to see this. There are always going to be back room companies out there that want to save a few dollars and try to maximize their margins by avoiding the trouble and the expense of testing and certifying their products.

Some consumers will think they are getting a pretty good deal by buying a cheaper or uncertified cable to connect to their very expensive phone or other pricey device. You might save five bucks on a cable that is not certified, you plug it into your nine-hundred dollar phone, and now you have real problems.

The folks driving the USB specifications and the compliance testing are really doing a great job to mitigate those risks, but these threats to safety, security and really the hard-earned brand integrity of USB bear constant attention from the people who write the specs for USB and from companies like us.

Mark Gordon, Microchip Technology: There’s a large push by the computing industry for implementation of 10 Gbps USB (USB 3.1 Gen2), however there’s a very limited application set for that kind of performance. Investment in Power Delivery for 100W and the need for a smaller more cost-effective connector, like USB Type-C, makes sense from a technology perspective. The investment to develop the new USB 3.1 Gen2 specification, however, is quite large, extending the payback for a 10 Gbps interface potentially longer than traditional silicon development investments. Case in point, the majority of the USB deployments remain at USB 2.0 (480 Mbps) data rates. USB 3.0 took five years to reach critical mass. The same is expected (if not longer) for USB 3.1 Gen2.

Mick Posner, Synopsys: USB standards and compliance tests are developed by some of the industry titans to ensure product interoperability. Therefore, it is vital for the continued success of USB that interoperability and compliance testing be performed on all USB IP, chips and products before they enter the marketplace. Synopsys, as the #1 provider of USB IP with more than 3,500 customer tape-outs and 3.6 billion units shipped to date, invests heavily in all aspects of USB from specification contribution through internal and external compliance programs and certification development. Not all USB IP is created equal so choose cautiously. Using IP that has not been tested or certified means not having your design pass compliance and having non-interoperable products on the market. So make sure your USB IP is certified, period.

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