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Sapera LT
PC2-Comp Express
Overview of Video Bandwidth and System Limitations
Some high resolution/high frame rate cameras can output more data than can be transferred through
the host computer PCI bus. A successful imaging application must account for the camera data
bandwidth and possibly control frame rate or image resolution to bring the bandwidth requirements to
within the system’s limitations.
Bandwidth is defined in two different ways. Peak bandwidth is the highest data rate occurring at any
time during the data transfer. The average bandwidth is the amount of data per unit of time being
transferred.
Each is calculated as follows:
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Peak Bandwidth (MBps) = Pixel Clock Frequency *Bpp *nb channels
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Average Bandwidth (MBps) = Frame Width *Frame Height *Frame Rate *Bpp
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where:
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MBps = Megabytes per second
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Bpp = Bytes per pixel
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nb = number of …
When the bandwidth required by the frame grabber exceeds the capacity of the PCIe bus, the
following techniques can reduce and optimize the average bandwidth.
Bandwidth Reduction Techniques
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A linear relationship exists between the average bandwidth required and the acquisition image
height. For example, if four cameras of 1K x 1K, at some frame rate, need to transfer 160MB per
second of data, those four cameras at a 512 x 1K resolution will only need a bandwidth of 80MB
per second.
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Using the Planar Transfer mode, where each color plane is sent to its own host buffer, can reduce
PCI traffic by 25%
3-bytes to transfer (RGB) instead of 4 (xRGB).
Bandwidth Optimization Techniques
The following techniques are suggestions for applications that require all possible optimizations from
the host system. Implementing these suggestions require a thorough understanding of your computer
system setup and its BIOS controls.
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Allocate a separate IRQ for the frame grabber. BIOS settings can be used to manually assign the
IRQ number to a particular PCI slot. As an alternative, the Window Device Manager can be used
to force a specific IRQ to a specific PCI slot.
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Minimize the PCI latency timer in the BIOS setting; the value is given in CLK cycles.
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Avoid any hard drive write/read operations and network access through PCI LAN interfaces
during intensive image transfers by the frame grabber.
Important:
Some computer systems do not provide the BIOS controls described. Review your system
manual.
Summary of Contents for PC2-Comp Express OC-P2EM-COMP0
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Page 38: ...32 Theory of Operation PC2 Comp Express ...
Page 46: ...40 Technical Reference PC2 Comp Express ...
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Page 65: ...PC2 Comp Express Sapera LT 59 EMI Certifications Class A both FCC and EC ...
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