A PCIe-based system can employ multiple frame-grabber boards and provide each with a link to system memory. Because the bandwidth of a PCIe link is dedicated to the data transfer it carries, each frame grabber in the system can operate at its full speed without affecting the others. This, in turn, allows the inspection system to provide maximum throughput.
Another nice feature of PCIe is its independent, bi-directional bandwidth. This bi-directional capability is poised to help simplify co-processing in machine vision systems. As Gigabit Ethernet cameras began making inroads into general purpose machine vision applications, the need to offload from the host CPU the task of converting the GigE Vision packets into usable images became increasingly evident. A Bayer color GigE camera sending data at 100Mbytes/sec., for example, requires the host computer to spend tremendous amounts of valuable CPU clock cycles simply converting and decoding images into usable formats.
The CPU can be off-loaded, however, by utilizing a general-purpose co-processing board and a network interface card (NIC) on the PCIe bus. The camera sends its data to the network, and the NIC forwards the data to the coprocessor across PCIe. The coprocessor performs both packet conversion and Bayer decoding in real-time, then streams the data to system memory using the transmit half of its PCIe link. This high-speed data transmission, processing, and storage can all occur without CPU intervention, freeing the CPU to perform more critical analysis. This approach also allows the creation and use of standardized PCIe coprocessor cards rather than the proprietary mezzanine cards being used in PCI systems, simplifying system design and lowering cost.
This kind of growth potential along with the current benefits of PCI Express will ensure its adoption in many coming generations of PCs. Its attributes applied to machine vision systems will, in turn, allow these systems to provide greater throughput and multi-channel capabilities unattainable utilizing the PCI bus.