Appendix
A
GigE Network Configuration
A-34
Getting Started with Visionscape GigE Cameras
With the InterPacketDelay (IPD) set to zero the camera sends one packet
of data and then immediately sends the next (actually there is a minimum
delay of approximately 96 nanoseconds). This process repeats until all
the packets that make up an image have been transmitted. Increasing the
IPD tells the camera to take a short break between sending each packet
which might give other devices a chance to send some of their data.
The IPD is a multiple of ticks. For GigE, 1 tick is 16 nanoseconds. To run
4 CMG20 cameras at a maximum of 5 frames per second setting the IPD
to 15000 works. This is a delay of 240 microseconds between each
packet.
The following calculations show how this works:
–
15,000 ticks is 240 microseconds.
–
2MB image is approximately 222 9k packets.
–
222 * 240 microseconds = 53 milliseconds.
–
The camera could run at 16 fps, which is 62 milliseconds per
frame.
–
We have just increased the overall time per frame from 62
milliseconds to 62 + 53 = 115 milliseconds. This is more than 5
frames per second so we should be all set (depending on
exposure time).
The final step is to shut down the Backplane (if it is running) and cycle
power to all the cameras. When Visionscape comes up the next time with
jumbo packets enabled in the registry and the NIC, it will be able to tell the
cameras to use jumbo packets too.
Now you can use the cameras without any missing packets or dropped
frames.
NIC Parameters
GigE cameras need GigE NICs (network interface controllers). NICs can
come built-in to a PC on the motherboard or as PCI or PCIe cards and
there are also some USB-to-Ethernet adapters available.
Microscan recommends the use of NICs that make use of the Intel
Pro/1000 chipsets.
