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PCI EXPRESS RECEIVES ATTENTION
PCIe already has become the de facto standard for graphics I/O within new PCs and increasingly is appearing in fast data acquisition and machine vision applications. The first PCIe frame grabber was introduced just over a year ago. Today, there are about a dozen manufacturers producing PCIe frame grabbers with widely varying capabilities. Currently, no cameras have been designed with a PCIe interface although this may occur in the future. PCI, the long-established PC bus standard, uses a shared, 47-pin, 33-MHz, 32-b parallel bus and can achieve a 132-MB/s data rate. The fastest PCI-X variant with a full 64-b implementation and a 133-MHz clock reaches a 1-GB/s rate. In contrast, a PCIe lane uses two two-wire, 2.5-GHz, low-voltage differential-signaling serial buses, one for each direction of traffic. Data and control signals are sent as packets, eliminating the need for additional wiring. Currently, ×1, ×4, ×8, and ×16 versions are available, making possible near 4-GB/s bandwidth. Even the ×1 bus boasts a 250-MB/s capacity, more than sufficient for many medium-speed cameras. Also, PCIe lanes are dedicated peer-to-peer links, meaning that bandwidth is not shared. There’s no doubt that adopting PCIe has eliminated or greatly reduced the I/O bottleneck presented by PCI. However, you may question whether the problem of restricted bandwidth simply has been pushed farther along to another part of the PC system. Indeed, you can’t present a 4-GB/s data stream to a single hard disk. Instead, very high data rates require a redundant array of independent disks system with the necessary bandwidth, memory buffering, and capacity. Fully buffered dual in-line memory modules also are a fast storage solution. Chuck Petersen, lead designer at EPIX, commented, “Motherboards now can accept up to three PCI ×4 boards. We have tested motherboards that simultaneously handle two 625-MB/s image data streams. One board had eight slots for FBDIMM and was tested with 6 GB of memory. Further testing with up to 16 GB of memory soon will be undertaken. PCIe is one part of coping with very high-speed image data, but a 64-b operating system also is important. By fully supporting 64-b Windows XP, we can capture data into 16 TB of memory.” The future availability of an enhanced version of PCIe with twice the present bandwidth is yet another reason that this bus is rapidly gaining support. However, not all applications require blinding speed, and there are several ×1 frame grabbers that can multiplex data from as many as four cameras. In American ELTEC’s PC_EYE/ASYNC, for example, each of four simultaneous monochrome analog channels can be digitized with 8-b resolution at up to 40 MS/s. The data is stored in separate memory regions and transferred under DMA control via the PCIe bus. In most current surveillance systems, the raw live video stream from a large number of cameras is displayed on a set of monitors, and security personnel respond to situations as they see them. Activity of interest must be manually tracked, and when an individual leaves one camera’s view observers must switch cameras and viewpoints. To improve upon this approach, Sven Fleck and his colleagues at the University of Tübingen (Tübingen, Germany; www.gris.uni-tuebingen.de) have developed what they say is an intuitive visualization approach in which the results of a surveillance system-the person’s path-are reflected in one consistent and georeferenced 3-D world model that is ubiquitously accessible.
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