USB Aims for Truly Universal

USB is making leaps and bounds to make it a truly universal connector. The mentality of not only advancing current technology, but branching out and re-using IP in new areas has rightly made USB a leader in the industry.

The USB protocol is expanding its application to become a completely universal connection medium. It seems that the USB Implementers Forum (USB-IF) will not stop until the USB cable can be used for any technological connection that one can imagine. USB has pressed forward in the standard protocol by releasing the SuperSpeed USB 3.0, but is also developing specifications to expand the applications of USB. The increased data rate provided by SuperSpeed has greatly increased the possibilities of product extension, and the IF is taking full advantage. The three most relevant specifications to making USB a truly universal transfer protocol are Super Speed Inter-chip (SSIC), USB Power Delivery and USB Audio/Video (A/V).

Super Speed Inter-chip (SSIC) Optimized for Mobile Devices
The USB 3.0 promoters group has teamed up with the MIPI Alliance to define SSIC, a low-power, high-bandwidth chip-to-chip interconnect based on the USB protocol over the MIPI M-PHY. The M-PHY makes use of Reference M-PHY MODULE Interface (RMMI) instead of the USB standard PIPE interface between the link and the physical layer (Figure 1). Because of its low power consumption, SSIC is being optimized for internal use on mobile devices. Using the USB protocol in a chip-to-chip solution is not a new idea all together. Hi- Speed USB utilized this idea as well, using high-speed inter-chip (HSIC) to replace I2C. The newer SSIC will feature much higher data rates and power efficiency.

Figure 1: Example SSIC implementation using minimal topology modification in the link layer and above. All SSIC specifics are contained in the PHY adapter level including the PIPE3 interface to RMMI bridge.

Current chip interconnects have begun to limit the capabilities of smartphones and tablets, but SSIC plans to expand capabilities rather than limit them. The target for per-lane data rate over SSIC starts with 1.2 to 2.9 Gbits/s and will eventually reach 5.8 Gbits/s. On the power threshold, the aim is for between 1 and 5 picojoules per bit per second. In high-speed mode, the power level would amount to an average of approximately 20 milliwatts. These power levels paired with low pin count and high data rates make this technology very attractive to the mobile device industry.

Another advantage of SSIC will be its cost of development. Current competing technology offers its specification to peripheral chip designers for a one-time fee of $100,000. SSIC will be royalty-free to all members of the MIPI Alliance and the USB 3.0 Promoters group that are at the adopter-level when using the technology for “mobile terminals with voice capabilities.” This specification is not the only one that adds a promising power twist to the USB protocol.

USB Power Delivery Boosts Charging Power
The standard USB 3.0 specification constrains the power delivery over a USB cable to a mere 4.5 watts (5 volts, 0.9 amps). USB 2.0 is even lower at 2.5 watts (5 volts, 0.5 amps). These power levels work fine for charging small form factor devices like smartphones and cameras. For larger electronics such as monitors, printers and laptop PCs however, 4.5 watts doesn’t even come close to supplying the required power. Headed by the USB-IF, developers are working on a USB Power Delivery specification that will deliver power levels up to 100 watts (5 volts, 20 amps), an adequate level for many more consumer electronics (Figure 2).

Figure 2: With USB Power Delivery, a much larger range of consumer devices will be able to utilize power over a USB cable. This figure shows some of the added device types as compared to other USB specifications.

Negotiating a device’s voltage and amperage upon connection (already included in the USB specification), along with the new, higher power levels, creates a unique powering situation. Any USB connector will be capable of supplying power to low-power devices like mice and keyboards, high-power 24-inch monitors, and everything in between. More wattage is not the only thing that this new spec will offer. Bidirectional power delivery is also included, allowing one to change power source without touching the cable between two devices. Allowing charge direction to change creates a type of shared power when devices are connected. Whichever connected device has more power could charge the other and, in a way, equalize the power levels. The power delivery should operate on current standard cables and connectors, making for a near seamless transition to this new addition to the USB family.

This development could easily eliminate the need for peripheral devices to have anything more than one USB cable plugged in to operate completely with a host PC. Removing the need for an AC/DC power converter will drive down prices of any USB product that was formerly externally powered as well. Imagine sitting at your desk and having only one clunky power block plugged into your wall, and everything else powered through USB. That mess of wires behind the desk may be seeing its final days. A notebook PC could rely solely on a USB connection for power. With help from USB Power Delivery technology, we can see a scenario where your computer monitor can have one cable connected that supplies not only power, but also audio and video with another one of USBs new specifications, USB A/V.

Promise of Lower Cost High-Definition A/V Delivery
Today, high-definition audio and video delivery only brings to mind HDMI as a technology that can supply true HD video with sound. HDMI is a newer technology that started in the early 21st century that delivers great quality and reliability from my experience. The only downfall that comes with the HDMI cable is the price. A high-quality, one-meter cable can cost anywhere from $20 to $60 at your local electronics store. On the other hand, reliable USB standard cables can be found at the same store for fewer than $10. It is for this reason and many others that there is excitement to see USB A/V hit the market.

USB has already solidified its name in the market as a reliable data-transfer mechanism and is a standard port on every computer on the market. Boasting up to 10x the speeds of Hi-Speed USB 2.0, SuperSpeed USB 3.0 will be amply capable of transferring high-definition audio and video over its established, dependable protocol. The biggest challenge with transferring audio and video comes with achieving continuously correct timing. A small error in an audio stream can be heard by a user and is considered unacceptable. Video on the other hand is a little more lenient. One or two pixels in error are mostly unrecognizable, but missing a whole frame can ruin the user’s experience. Eliminating errors while keeping the audio and video in sync makes an A/V connector difficult to create with quality that we expect from USB. Fresco Logic was able to give a live demo of the A/V technology at Computex 2012 Taipai, boasting full HD over a USB 3.0 cable to a secondary monitor. Although there is no specific date as to when the A/V technology will come to the consumer, the aim is to use it in ultrabooks, tablets, smartphones, pico projectors, HD displays and TVs. It seems as though USB A/V will become a direct competitor with HDMI and boast a much lower price point due to USB’s low cost implementation. Could we see a shift in the audio/video connection market? I guess we will just have to wait and see.

Leaps Toward Universal
USB is making leaps and bounds to make it a truly universal connector. The mentality of not only advancing current technology, but branching out and re-using IP in new areas has rightly made USB a leader in the industry. Seeing all these advances in USB technology makes me think about the future: Today’s computing power of a laptop computer held in the palm of your hand. USB wall sockets throughout your house instead of the standard three-prong outlet that we use today. An entertainment system using only USB cables for data and power. All of these ideas could soon be a reality for the common consumer.

What could be the next? USB connectors throughout a house provide the possibility of having a fully networked “smart house.” An Internet connection could be achieved by simply plugging in a device to be charged. Looking ahead toward the next generation of standard USB, the challenge becomes how far the transfer speed can be pushed without making major changes in the design that USB has used for years. Communication mediums are beginning to test the limitations of the traditional copper wire. Creativity and pioneering are crucial to the continuing development of technologies that are used every day. The possibilities are endless and it’s innovative technologies like USB that are helping to lead the way.

Tim McKee is a hardware/software engineer for Intel I/O Technology and Standards. He is a recent graduate from Oregon State University with a degree in electrical and computer engineering. He currently works on hardware proof-of-concept prototypes and compliance software.