Experience has also shown that simply using a bridge chip to upgrade a design runs into system initialization issues. As with the slot problems of commercial motherboards, the BIOS may create challenges. During allocation of system resources, some BIOS software has difficulty reaching through a bridge to determine card resource requirements. Some bridge chip vendors have augmented their designs to address these issues, but this leaves system developers with a need to check the compatibility of motherboard BIOS and card bridge chip to avoid problems.
The second design approach is to make PCIe the peripheral card's native interface. Taking this approach eliminates the need to check for compatibility as there is no bridge device to confuse the BIOS. A native PCIe design also allows the card to offer maximum performance. Without the restriction of the PCI interface, the card's hardware can fully utilize the bandwidth of the PCIe link.
Many vendors have followed the bridge approach to enter the PCIe market quickly at low cost. DALSA, however, has chosen to use a native PCIe design approach in its next generation Camera Link frame grabber and vision processor product lines. This approach provides the maximum degree of motherboard compatibility attainable, freeing system design from artificial limitations. It also ensures that developers have a single point of contact for system design questions; there is no need to coordinate with a BIOS provider to resolve issues.
PCIe Applications in Machine Vision
The high speed and dedicated bandwidth available to DALSA's frame-grabber boards because of their native PCIe interface enables users to address a wider variety of machine vision applications than earlier PCI devices. One application that benefits is the use of high-speed line-scan imaging for web inspection. Under the 32-bit addressing limit of PCI, line-scan systems needed to artificially break the image into frames of a size that would fit into the 2-GigaByte addressable memory space. This framing activity interrupts the data flow and complicates the image processing used in the inspection process by introducing arbitrary image boundaries. Designing 64-bit compatibility into a PCIe interface allows virtually unlimited frame sizes, permitting the web inspection to proceed on a more continuous basis.
Another application that benefits from PCIe's attributes is multi-angle inspection. Such systems use multiple cameras to examine an object from several directions simultaneously. This multiple view allows a system to inspect all surfaces of an object without requiring the object to be manipulated. A conventional PCI-based system that offers multiple image-capture channels, however, must share the system bandwidth among the channels. This sharing quickly becomes a bottleneck, lowering the inspection system's throughput.