USB Brings Cost and Connectivity Advantages to Imaging

As published in Quality Magazine
March

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USB is the most prevalent method to connect computers and peripheral devices. Taking a survey of my desk there are a multitude of devices &#; a smartphone, headphones, a camera, mouse and keyboard &#; that rely on a USB connection.

Thanks in large part to its ease-of-use, USB dominates consumer-to-computer connectivity applications and is being rapidly adopted across other markets. For example, home-based medical devices that track general health, or more complex systems that monitor a patient&#;s response to therapy, benefit from the plug-and-play simplicity of USB.

Often these products store data in memory until they are plugged into a PC. Data can be analyzed locally &#; a fitness tracker shames us into moving more &#; or is transferred to a physician&#;s office for evaluation. For the majority of these applications, USB is a simple method to support the bandwidth required to transmit data-intense information. However, there&#;s no real-time requirement for data delivery. The few seconds its takes to transmit data from the device to the computer doesn&#;t impact a patient&#;s or physician&#;s ability to monitor health or a response to treatment.

The same is not true in machine vision, where automated decisions must be made within milliseconds or faster. As a result, the imaging industry was initially slower to adopt USB as an interface option due to its previous transmission limitations. As the USB standard has evolved and bandwidth capabilities have increased, new opportunities for the technology are emerging in the traditional imaging market. More so, as machine vision moves into new markets, USB is a recognizable and easy-to-use interface for less technical end-users.

USB and Machine Vision

While USB interfaces have been widely adopted across other markets, the bandwidth supported by earlier versions of the standard was insufficient for imaging applications requiring uncompressed, raw data for real-time image analysis. This changed with the third major version of the USB standard &#; USB 3.0 or SuperSpeed USB &#; which provides 10 times the bandwidth of USB 2.0.

Backed by this bandwidth boost, the vision industry ratified the USB3 Vision standard in , providing designers with a framework to address performance, cost, and usability requirements in real-time imaging systems. Data is transmitted directly to existing ports on a computer with sustained throughputs approaching 3 Gbps; surpassing the performance of Camera Link Base configurations and rivalling Medium configuration, but without requiring specialized frame grabbers at endpoints to capture data. By eliminating the need for frame grabber cards, designers can choose from a wider range of computing platforms, including laptops, tablets, and single-board or embedded processors.

While the imaging industry adopts USB 3.0, the USB Implementers Forum (USB-IF) is continuing to evolve the technology. As computing devices get thinner, USB-C is now an increasingly common connecter to transmit data and power for new laptops. The USB 3.1 Gen 2 protocol offers 10 Gbps data transfer and 100 watts of power. More recently, the USB-IF announced USB 3.2 with a theoretical maximum data transfer rate of 20 Gbps.

Advantages and Challenges of USB3

While GigE Vision dominates the machine vision interface market, USB 3.0 has quickly reached deployment levels that rival more established solutions (Figure 1).  Bandwidth has been a major driver for the initial adoption of USB3 Vision, but manufacturers shouldn&#;t ignore its cost and design advantages.

The thinner, lighter USB 3.0 cable is easier to route than bulky Camera Link cables and connects with &#;plug-and-play&#; ease, allowing faster setup and teardown of inspection stations. To enhance reliability, the USB3 Vision standard specifies locking connectors for the cables.

Video, control data, and power are transmitted over a single cable, reducing cabling complexity and eliminating the need for an external power supply for cameras, resulting in reduced cost and system footprint. USB 3.0 reduces system overhead and CPU usage by using asynchronous signaling, rather than the polling mechanism of USB 2.0, and direct memory access (DMA) transfers. As a result, more processing power can be dedicated to the vision application.

USB3 Vision is building a strengthening market position in vision applications that value high-bandwidth point-to-point video transmission. While the inherent networking and multicasting of GigE Vision is advantageous in multi-image source and endpoint systems, multiple USB 3.0 cameras can operate in parallel on a single bus by employing an off-the-shelf USB 3.0 hub. In comparison, each Camera Link camera would require its own dedicated cable and frame grabber.

Distance remains the last hurdle for USB 3.0 interfaces. Multiple vendors now provide active cabling solutions that extend the potential distance between imaging sources and processing units far beyond the initial three to five meter range.

USB3 Vision in Imaging Applications

Virtually every camera manufacturer now offers USB 3.0 products, while external frame grabbers are also available that convert images from existing cameras into a USB3 Vision video stream. USB3 imaging devices are being designed into a number of applications that require high resolution and frame rates, including document scanning and print verification.

Barcode print verification systems help lower costs, increase productivity, and reduce errors by providing detailed quality analysis to ensure high read rates in automated quality inspection and warehouse processes. If printing errors are not detected quickly and automated reading systems can&#;t identify the product, barcodes may need to be manually entered into supply chain systems or unverified products must be destroyed. This results in disrupted manufacturing processes and additional costs.

Print verification systems rely on machine vision hardware and software to ensure barcodes meet industry standards for readability in automated processes. USB3 Vision imaging products can help lower the costs of these systems by identifying unreadable barcodes early in the manufacturing processes.

In this application, the portable barcode verification unit employs a CMOS image sensor to capture a high-resolution image of the barcode. The video feed is converted into a USB3 Vision image stream and transmitted over an off-the-shelf USB 3.0 cable directly to a port on a computing platform where barcode readability is verified. By eliminating the need for a PCIe frame grabber to capture image data, system designers can employ lower-cost computing platforms, including laptops, for barcode analysis and verification. In addition, power over USB simplifies cabling and lower component costs.

Ease-of-use is another key advantage of USB 3.0 video connectivity, particularly in applications where end-users are not vision experts. Microscopy systems for medical quality inspection uses often use a Camera Link camera to transmit images to a computer for analysis and display. The Camera Link video interface requires bulky, specialized cabling and a PCIe frame grabber to capture images at the computer, resulting in more complex systems, higher costs, and limited component selection.

Instead, external frame grabbers can convert the Camera Link image feed into USB3 Vision-compliant video. The uncompressed video is transmitted with low, consistent latency directly to an existing USB 3.0 port on a laptop used for analysis and display. The plug-and-play performance of USB 3.0 allows for faster setup and teardown of inspection stations.

The Future of USB in Vision

The vision market is increasingly leveraging expertise developed for other markets to help deliver advantages in imaging applications. Gigabit Ethernet, USB 3.0, and more recently NBASE-T are all examples of networking technologies bringing new cost, performance, and usability benefits to automation systems.

As imaging manufacturers and system integrators adopt USB 3.0 into their products, we will all be watching closely to see how quickly the consumer market adopts higher-bandwidth USB interfaces. As more devices on our desks begin to support USB 3.x and beyond, we can expect the next wave of higher bandwidth imaging devices for the automation market.

Silicon Imaging 
USB 2.0 Cameras: 

Setting the Imaging world on fire!  

The high speed image capture and connectivity market is about to undergo a revolution. The need for purchasing and installing a custom frame grabber or IEEE- interface card will soon become a distant memory.   The new standard will be to connect your high speed megapixel machine vision and line scan cameras with a single 4-wire cable directly into a 480Mbit/sec (megabits per second) USB 2.0 port, soon to be found in every new motherboard produced with Intel P4 chipsets.  These new USB 2.0 vision cameras will transfer precision 8 or 12-bit digital gray scale or color image data, eliminating the sampling jitter of traditional analog RS-170 or NTSC systems, at speeds 40x faster than the predecessor USB1.1 and 20% faster than Firewire (aka. IEEE- or Sony i-link) devices. This interface will also provide bi-directional serial communication for camera setup and control, triggering, strobing and other I/O signaling.  One of the most convenient benefits, especially for those imaging executives and sales engineers traveling with the latest lightweight laptops, is not having to carry an additional power supply; these cameras will be powered thru the same USB cable.  For the vision system end-user, the benefit will be a lower system cost than previous camera and frame grabber solutions and plug-n-play installation. 

MegaCamera-2.0: See the light!

The Silicon Imaging MegaCamera-2.0 family offers a broad range of models based on desired resolution, frame rates, capture method and cost, each optimized for full USB 2.0 speed performance.   All cameras provide 12bit precision digitizing, sampling rates to 50MHz, software programmability of exposure, gain, clock, 8/12 bit transfer and triggering modes, very small size and bus powered capability.   The SI- is the worlds first 3.2 Megapixel USB 2.0 camera, capable of x at 15fps or x HDTV resolution at 24fps.  An 8x digital pan/tilt/zoom function enables a region of the image to be readout at video rates and moved through the scene for video conferencing and surveillance applications. For lower cost application the SI- provides x resolution at 30fps.  For scientific analysis, medical imaging and stop-motion machine vision applications the SI-F has x resolution up to 30fps with large 12um pixels, Full-Frame shutter, binning, adaptive readout and windowing.  For high speed motion capture and sports analysis, the SI-320F can capture and recording 320x240 resolution video at over 500 frames per second.  All models are available in either monochrome or Color RGB Bayer formats with products starting under $995. Yes, this includes a cable.

USB Background

The Universal Serial Bus (USB) standard was originally developed in , to minimize the number of ports in the back of the PC.  The major goal of USB was to define an external expansion bus which makes adding peripherals to a PC low cost and as easy as hooking up a to a wall-jack.  USB featured a maximum bandwidth of 1.5Mbit for low speed devices such as mice and keyboards, and a maximum bandwidth of 12Mbit for higher speed devices such as web cams, printers, scanners and external CD-RW drives. Frustrated by Apples royalty fees on firewire devices, in April , seven industry-leading companies, consisting of Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC, and Philips published the specifications for USB2.0. It has taken approximately 2 years for USB 2.0 to become adopted as a mainstream USB1.1 replacement.  In just a few short months USB 2.0 will be the high speed PC peripheral connectivity choice over IEEE-.

 

Introduction to USB 2.0

The USB 2.0 specification extends the maximum speed of the connection from 12 Mbps on USB 1.1 up to 480 Mbps (60MBytes/sec).  This enables the transfer of x images at 24fps (frames per second) for high-definition video conferencing or 320x240 images at 500fps for high speed video motion analysis.  The transition to USB 2.0 will be seamless, since USB 2.0 is both forward and backward compatible with USB 1.1. Older peripherals will simply plug into new USB 2.0 capable PCs and Hubs.  The USB connectors and cables are even identical.   It is even possible for a high speed USB 2.0 device to plug into a legacy USB1.1 port and simply operate at reduced throughput.   Both Hi-Speed USB 2.0 and original USB 1.1 peripherals can operate on a computer at the same time. The new USB 2.0 expansion hub design manages the transition of the data rates between the high speed host and lower speed USB peripherals, while maintaining full bandwidth utilization.   Up to 127 USB peripherals with 5 levels of hubs can be connected to a single USB host controller.  With 5 Meters (16.4 feet) of cabling between devices, a network of cameras, sensors, data acquisition, and I/O devices can physically extend up to 30 Meters (98 feet) from the PC.  A peripheral can either be self-powered or bus-powered, with up to 500mA of consumption. To satisfy the needs of low-power embedded and portable computer applications, a power-management mechanism is also incorporated.

Getting Started - Enumerate it!

A USB device can be plugged in anytime, even while the PC is turned on. The installation process is truly plug-and-play; no hassles with jumpers, IRQ settings, Interrupt or incorrect drivers.  To achieve this almost magical connection process, the PC and peripheral, in our example the camera, go thru a detailed electrical handshaking and data setup procedure. A high-speed camera initially attaches to the PC USB controller as a classic full-speed (12Mb/sec) device.  The camera then signals it is high-speed capable. The host controller responds to indicate it is also USB 2.0 capable and begin communicating at the high-speed rate.   When the PC operating system detects that a USB device has been plugged in, it automatically assigns the peripheral a unique address.  All further communication to that device uses this address, thereby distinguish it from other devices on the bus. The PC then learns the devices capabilities, by requesting its "descriptors".  This information is stored within the power and bandwidth needs and required driver. From this information, the PC automatically loads the device&#;s driver into the operating system and the device is ready for use. This sign-on process is called Enumeration.

USB2.0 Speed throughput

In USB, the PC is the master and the peripherals are slaves. The PC makes requests and peripherals respond.  A typical USB transaction has three stages.  First, a Token packet is sent by the PC with the address of the device and an indication of the desired direction of data transfer.  If data is being sent to the peripheral, such as camera setup commands, it is an OUT request.  If data will be sent from the peripheral to the PC, such as image data input from a camera, it is an IN request.  Next is the data packet transfer stage.  A data packet can have up to bytes along with a CRC value for error checking.  The third stage is the handshake.  Once the data has arrived successfully, a packet is sent to ACK or acknowledge it.  For streaming data which do not require error checking or handshaking, for slightly reduced overhead, can be sent in isochronous mode.  For guaranteed data accuracy, in Bulk mode, packets with errors are retransmitted.  Every 125usec a bus synchronization signal call Start-of-microframe is issued.  During each microframe the PC will perform multiple data transfers.  For maximum bandwidth utilization, up to 13 packets containing 512 bytes of data can be transferred during each microframe,.  This translates to over 53 Mbytes/sec throughput (13 packets/uFrame * 512 bytes/packet * 8uFrames/ms), including protocol and handshake overhead.  From the programmers perspective,

Intel sends USB 2.0 into ubiquity

In May , Intel sealed the success of USB2.0 connectivity.  Intel released a family of chipsets called 845E, 845G and 845GL for both the Pentium-4 and Celeron processors.  These chipsets which include the ICH4 South Bridge chip, all have an embedded USB2.0 enhanced host controller interface and hub, capable of supporting up to 6 high or low speed ports.   PC OEMs will no longer need to purchase and incorporate an additional peripheral IC to implement the interface; it will effectively come for free.  Further accelerating market domination, Intel also released a family of motherboards based on these new chipsets.  The next day after the debut, Dell released its first desktop machine with this new chipset architecture, the S, with a retail price of $789!  Yes, that includes a monitor.

Since the ICH4 connects directly to the memory controller, (aka. North Bridge chip), over a 266MB/s (32bit/66MHz) hub interface, it can simultaneously move data from the USB2.0 at maximum rates without reducing the bandwidth capacity of the 32bit/33MHz PCI bus. For applications requiring multiple high speed simultaneous capture, additional USB2.0 PCI adaptor cards can be added into the system without saturating the bus. This new PC architecture provides the same system improvement for digital video capture as the AGP bus provided for increased throughputs to a display.  The result is more inputs, speed, resolution, or frame rate at lower costs. 

Microsoft not in the Driver Seat?

Earlier this year, there was some industry buzz that Microsoft may not be strongly backing the emerging USB2.0 standard, as the supporting drivers were not included with the launch of WIN-XP. The main issue was that the USB2.0 drivers were not completed at the time of launch of XP and there were not enough peripherals on the market yet for testing.  The delay was simply to prevent potential incompatibilities, reminiscent of the early days of Firewire, and to insure clean installation and operation for the new generation of peripherals.  Microsoft has since released a driver for Windows XP and has upgrades planned for Windows Me and Windows .  However, Microsoft has stated it will not provide USB 2.0 driver support on Windows 9x or earlier Windows operating systems. Adaptec, a recognized leader in USB2.0 Adaptor cards and hubs, has jumped in to fill this market need by developing and delivering drivers for their USB2.0 host products for WIN 98, XP, ME and .   The Linux community has even recognized the imminent growth of USB2.0 and has already released driver support in their latest kernel.

CameraLink still the king of speed

CameraLink, a connectivity standard for industrial digital cameras and frame grabbers, will continue to be the interface of choice for the highest speed imaging applications.  In its base configuration, CameraLink can transfer at up to 1.6 Gb/sec. In Full configuration, using 2 cables, the rate is extended up to 4.8 Gb/sec.    This extremely high throughput has enabled the Silicon Imaging SI- CameraLink camera to achieve sustained real-time 30fps 12-bit video at 3.2 Megapixel resolution, or 1.2 Gb/sec peak transfer speeds.  To meet the increased transmission capacity of this interface, CameraLink frame grabber manufacturers have recently expanded their product offerings to include 32bit/66MHz and 64bit/66MHz PCI cards with multiple channel input capability. At the entry level, 32bit/33MHz PCI cards provide price/performance value with products starting as low as $695. No, that does not include the cable.

USB 2.0 versus Firewire IEEE- 

The primary difference of IEEE- is its peer-to-peer topology, which enables peripherals, such as a VCR and television, to communicate between each other without the need for a master PC.  This feature does not provide any value in a system where the PC is doing your image capture, processing, display, storage and networking.  The USB Master/Slave architecture was chosen as the best way to keep peripheral costs to a minimum.   Silicon vendors estimate that peripheral controllers require four to five times more gates to implement the interface than a comparable USB 2.0 peripheral.  The "smarts" are placed on the PC side, eliminating the costly intelligence required for every USB peripheral device.  In addition, USB has remained royalty free, making inexpensive peripherals possible and avoiding the burden of licensing.

Category

USB 2.0

IEEE-a

CameraLink

Topology

Master-slave, OTG

Peer-to-peer

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Master-slave

Bit rates

480 Mbits/s

400 Mbits/s

1.6 Gbit/s, 4.8 Gbit/s

Transaction intervals

125 microseconds

125 microseconds

Synchronous

Bus master

Dedicated

Allocated at bus reset

PC

Signaling

Current mode differential

LVDS, optical

Multiplexed LVDS

Cable Distance

5 M,
Up to 30M with 5 hubs

4.5 M,
more with repeaters

10M
max

No. of Wires

4

6

26, 52

Bus Power Consumption   

Up to 500mA @ 5V

Up to 1.5A

no

Licensing

No

Licensing agreement and royalties

No

Main applications

PC-centric

Consumer electronics

PC-centric

Devices in network

127

63

1

The base link speed of USB2.0 at 480Mbit/sec is 20% faster than Firewire's 400Mbit/sec rate.  For the past two years, proponents would show you a specification for b with supported data rates in excess of 800Mbit/sec.  To date, no silicon manufacturer is in production with b higher data rate devices, primarily due to lack of market demand.  When, and if, these devices are finally introduced to the market, they will have several strikes against its implementation.  First, they will likely be highly targeted for Disk Drive Interfaces not imaging.  Second, the user will still be required to purchase a custom interface card which will immediately saturate the PCI bus, leaving no bandwidth for other devices to communicate.  Third, the interface will not achieve the higher data rates necessary for CameraLink connectivity applications. 

 

USB 2.0 OTG is On-The-Go

Due to the growing need for a direct interconnectivity between mobile devices (e.g. digital cameras, PDA, cell phones) and computer peripherals (e.g. printers, disk drives, home gateways) the USB 2.0 specification was recently supplemented with "On-The-Go" (OTG) capability. With this simple addition, an OTG peripheral will have limited host type capability and enable direct data transfer, peer-to-peer, to another USB or OTG peripheral, without PC intervention.  This is just another stake in the heart for IEEE-.  But for now, both USB 2.0 and are expected to co-exist on many consumer systems into the foreseeable future.

 

CONCLUSION

With millions of powerful 2.4 to 3.0GHz motherboards with USB 2.0 built-in to ship this year, with no additional cost to the user, there is no doubt that USB2.0 will soon become the de-facto standard for vision cameras and high speed image processing.  According to the In-Stat/MDR report "USB: The Universal Connection," USB 2.0 enabled devices will gain rapid acceptance in the marketplace with a 220% compound annual growth rate predicted between and .  USB 2.0 will be the preferred connection for most PC peripherals, whereas the IEEE interface will coexist with USB2.0 in audio/visual consumer electronic devices.  The USB2.0 will achieve faster speeds and lower costs than IEEE-.  However, CameraLink will continue to be king of speed.  For application requiring direct interconnectivity without a PC, you can plug in with OTG. A new generation of high performance digital cameras will help accelerate the adoption of USB2.0 in the imaging and machine vision market. The result for the system user and instrument developers will be increased resolutions, higher frame rates, lower costs, smaller size, increased portability and most likely a new generation of products to offer to offer to the market.

For more information on the Megacamera2.0, Cameralink and USB2.0 visit www.siliconimaging.com!