Vision & Sensors: USB 3.0 Interface: USB 3.0 Is Here!
Nowhere was this more evident than at the recent 2011 VISION show in Stuttgart, Germany. Camera vendors were busy flogging their wares, ranging from the invisible (“due to come out sometime in 2012”) to the real (“in production and shipping now”). The Automated Imaging Association was actively promoting a new interface standard. And users were asking a single, very important question: what does USB 3.0 mean to me? Here, we try to answer some of the common questions being asked, from the most basic (“What is USB 3.0?”) to the more difficult (“Which is better: USB 3.0 or GigE?”).
A New Bandwidth King?The effective bandwidth available via the bulk transfer method is around 400 MB/s. This is approximately 10 times the bandwidth available with USB 2.0 and 5 times that of 1394b (FireWire) and Gigabit Ethernet. While Camera Link is still the bandwidth leader at approximately 680 MB/s with a full eight-tap configuration, many customers may choose to sacrifice some pixels or frames per second in exchange for the easier to use and more cost-effective USB 3.0 alternative.
CPUs Rejoice: No More Polling!The USB 3.0 specification was created with the goal of building on the strengths of USB 2.0 while addressing many of its limitations. USB 2.0 employs a host-directed (aka, master-slave) architecture where every transaction either goes to or comes from the master (the host computer). Communication is half-duplex, allowing data to flow in only a single direction at a time. USB 3.0, which has an architecture more similar to PCI Express (PCIe) and FireWire, utilizes a unicast dual-simplex data interface that allows data to flow in two directions at the same time. This is an improvement over USB 2.0’s unidirectional communication model. USB 3.0 also supports direct memory access (DMA), which allows data to be read from/written to main memory without going through the CPU.
Although USB 3.0 is still a hosted device protocol, it now uses asynchronous signaling, which allows a device to notify the host when it is ready for data transfer. This significantly reduces system overhead and CPU usage compared to the polling mechanism in USB 2.0. In one streaming test, 280 MB/s of image data were processed and displayed on a monitor by an Intel i7 PC, with CPU usage between 1 and 2%.
More Power, and Backwards Compatibility, Too...USB 3.0 provides more efficient power management and increased power delivery over USB 2.0. The amount of current draw for USB 3.0 devices operating in SuperSpeed mode is now 900 mA, resulting in an increase in total power delivery from 2.5 W to 4.5 W (at 5 V). The USB Battery Charging 1.2 specification allows up to 7.5 W, giving USB 3.0 even more potential to power cameras equipped with some of the high-speed, high-resolution CCD image sensors on the market today. In addition to increased power, USB 3.0 offers an improved mechanism for entering and exiting low-power states, depending on whether a device is active or not, and eliminates power-consuming polling.
Although the USB 3.0 cable contains five new wires, it is still backward-compatible with USB 2.0, allowing users to plug their existing USB 2.0 camera into a USB 3.0-enabled computer. A USB 3.0 camera plugged into a USB 2.0 port will also work, provided enough power is provided.
What Operating Systems Support USB 3.0?While Windows 7 does not provide native USB 3.0 support, Microsoft has stated that Windows 8 will support USB 3.0. Apple has not announced specific plans to support USB 3.0 natively in their operating systems. Linux started supporting it in the September 2009 release of the 2.6.31 Linux kernel, but the current implementation does not adequately support video streaming applications. However, the Linux open source community is working on a suitable implementation and anticipates kernel-level support to come in the first half of 2012.
To address lack of USB 3.0 support in these popular operating systems, USB 3.0 host controller chipset manufacturers have created their own xHCI drivers. When evaluating USB 3.0 camera vendors, ask whether they rely on these drivers or whether they provide their own low-level xHCI driver, which may provide better performance and bus diagnostics and allow them to resolve issues faster
Who Are the Key USB 3.0 Players?The silicon required to provide low-level connectivity for USB 3.0 devices is readily available from companies like Renesas (formerly NEC), Fresco Logic, Etron, ASMedia, and Texas Instruments. These host controllers are being found on a wide variety of desktop and laptop motherboards, add-in interface cards and hubs. Market forecasts are calling for USB 3.0 to be on every PC by 2014.
USB 3.0 hubs and repeaters are already in production from companies like Diamond and IOI, and industrial cables with screw-locking connectors are readily available from companies like Alysium-Tech. Other USB 3.0 products made their debut at VISION, including the FireNEX-uLINK from Newnex Technology, one of the world’s first USB 3.0 active repeater capable of extending USB 3.0 signals up to 16 meters in length.
Is There a USB 3.0 Standard Like GigE Vision?The USB3 Vision standard is being developed specifically to provide a common camera control interface for USB 3.0 cameras. The USB3 Vision standard is hosted by the Automated Imaging Association (AIA), the global trade association for the vision and imaging industry, and is targeted for release in 2012. Like GigE Vision, the standard will enable compatibility between USB3 Vision-compliant software and imaging devices. The architecture of the standard is based on existing consumer hardware and draws from widely adopted vision standards, such as GenICam. USB3 Vision does not focus camera functionality, but instead four basic operations: device discovery, device control, event handling, and streaming data.
USB 3.0/GigE is Not a VHS/Betamax Story...When compared to the existing lineup of digital interfaces, USB 3.0 has its strengths and limitations. It offers increased 400 MB/s throughput and, like FireWire, provides cost-effective power and data over a single cable. However, while USB 3.0 is almost 10 times as fast as GigE, GigE can provide more power (15 W with Power over Ethernet) and its maximum cable length is superior. What is clear is that the two interfaces will co-exist as the predominant interface choices for industrial, scientific and traffic applications.
Reliability: Avoid the LemonsReliability is a function of the entire system, from the camera to the host computer. First look at what features are provided by the camera to maximize reliability. Features like screw-lock connectors that minimize disconnects; a frame buffer for image retransmission; on-camera power, temperature, and status monitoring; and in-field updatable firmware contribute to overall reliability.
The components that make up the image pipeline are also important. USB 3.0 interface cards are readily available at local electronics stores, but most aren’t intended for industrial applications. Ask the camera vendor whether they design and manufacture their own interface card. Also determine whether they rely on chipset manufacturer drivers or whether they provide their own low-level xHCI driver, which may provide better performance and bus diagnostics and allow them to resolve issues faster.
And finally, ask what hardware configurations the camera vendor has tested and found to work. If they know their stuff they’ll be able to tell you which motherboard/CPU/USB 3.0 host controller combinations work, and which may cause problems. Some Intel motherboards, for example, limit the PCIe Gen 2.0 x1 interface to Gen 1.0 speeds (2.5 GB/s instead of 5GB/s).
In SummaryWhen compared to the existing lineup of digital interfaces, USB 3.0 sits at the intersection of high data rate, power/data transmission over a single cable, ease-of-use, and cost-effectiveness. USB 3.0 promises to open up new applications in machine and computer vision, as well as non-industrial markets where USB 2.0 already has widespread acceptance. V&S
Tech TipsThe effective bandwidth available via the bulk transfer method is around 400 MB/s, approximately 10 times the bandwidth available with USB 2.0 and 5 times that of 1394b (FireWire) and Gigabit Ethernet.
The amount of current draw for USB 3.0 devices operating in SuperSpeed mode is now 900 mA, resulting in an increase in total power delivery from 2.5 W to 4.5 W (at 5 V).
While USB 3.0 is almost 10 times as fast as GigE, GigE can provide more power and its maximum cable length is superior.