Balluff MATRIX VISION GiGE VISION BVS CA-GX0-XAS2 Series, User Manual, Page: 78 / 94

4 FIRST STEPS
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7. Is the amount of the "Receive Descriptors" ( RxDesc ) of thenetwork controllerset to
the maximum (generally 2048 )?
This amount depends on the MTU. You can get a feeling about values with following
formula (per camera and per network port):
RxDesc >= 1.1 * PixelPerImg * BytesPerPixel
---------------------------------
MTU
Example 1: 1500 with 1.6 megapixels
RxDesc >= 1.1 * 1 .6M * 1
--------------
1500
>= 1170
Example 2: 8192 with 1.6 megapixels
RxDesc >= 1.1 * 1 .6M * 1
--------------
8192
>= 214
NOTE
Both examples are showing the RxDesc values based on packag-
es per image per second. Now, if you increase the images per
second you will see that you reach the amount of "
Receive De-
scriptors " very soon. Usually, the default values of the system are
between 64 and 256 and as a general rule too low. Also each use
of a "
Receive Descriptor " will result in a certain amount of CPU
time needed, which is why larger packets result in a better overall
performance.
If you are using small MTU values or if there is only a small value
of "
Receive Descriptors " possible, you have to enable " Interrupt
Throttling ". Interrupt throttling enables the network controller to
combine packets thus lowering the amount of interrupts.
The " Receive Descriptors " a.k.a. " Receive Buffers " (Intel
PRO/1000 network interface) can be found under " Performance
Options ":