Blackfly - CYLOD

Point Grey Blackfly Technical Reference
2 Blackfly Installation
Changing the packet size may impact throughput depending on the packet delay setting.
2.4.3.2 Packet Delay
The stream channel packet delay (SCPD) indicates the number of ticks (at the frequency of the Timestamp Tick
Frequency) to insert between each packet. The default packet delay is 400.
The Point Grey Timestamp Tick Frequency is normally 125,000,000 ticks/second, but can be verified by the the
GevTimestampTickFrequency GenICam feature, or the Timestamp Tick Frequency Bootstrap register (page 74).
The packet delay acts like a gap between packets during transmission. This delay allows the host to process the current
packet before the arrival of the next one. When you increase the packet delay value from zero, you reduce the
effective bandwidth assigned to the camera and thereby also reduce the possibility of dropped frames.
Increasing the packet delay is recommended when running multiple cameras through an Ethernet
switch.
Increasing the packet delay may require the frame rate to be reduced to meet the available maximum bandwidth.
Achieving a desired frame rate may require decreasing the packet delay.
To adjust the packet delay:
Packet delay for the camera can be adjusted using the FlyCap demo program, the GevSCPD GenICam feature (page
65), or the GigE Vision bootstrap registers (page 74). The FlyCapture SDK also supports configuring the SCPD. For more
information, consult the FlyCapture SDK Help.
2.4.3.3 Determining Bandwidth Requirements
The maximum bandwidth available is 125 MB. This includes image data, control data and image resends, which occur
when frames are being dropped. Each image and each packet has a certain amount of overhead that will use some
bandwidth. Therefore, when calculating your bandwidth requirements, you should not attempt to use the full
maximum of 125 MB.
If the packet size and packet delay combination exceeds the available bandwidth, frames will be
dropped.
To calculate your bandwidth requirements:
Determine your required resolution, frame rate, and pixel format (bytes per pixel)
(Height x Width x Frame Rate x Bytes per Pixel)/1000000 = Bandwidth in MB
For example, for an image that is VGA, 82 FPS, Mono8:
640 (H) x 480 (W) x 82 (FPS) x 1 (BPP) = ~25 MB
Once you have calculated your required bandwidth, you can allocate an amount to each camera by adjusting the
packet size and packet delay. Allocating a specific amount to each camera helps to avoid dropped packets due to a
data burst. You would do this in a set up with multiple cameras, or in a situation where the system bandwidth might be
limited or shared due to hardware architecture.
Revised 12/13/2012
Copyright ©2012 Point Grey Research Inc.
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