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Rad-icon 1520 Detector
Teledyne DALSA
Some system and network card configurations may have difficulty streaming and
handling jumbo packet data. If the system is having issues than it is advisable to disable
the Jumbo Packet setting, and use standard size packets of 1500 bytes for your
application.
Interrupt Moderation
Normally, each time a packet is received by the network card, the associated driver will
receive an interrupt. Obviously, when the packet rate is very high (that is, at high transfer
rate which is common for GigE Vision systems), this represents significant overhead.
Most network cards have introduced an interrupt moderation mode where the card waits
to have received a certain number of packets over a maximum period of time before
issuing the interrupt. This helps reduce the burden on the CPU as it can process multiple
packets during the same interruption.
The Intel Gigabit CT Network adapter provides a configuration parameter to manually
adjust the NIC interrupt moderation rate. By default the NIC driver sets this to Adaptive
where the interrupt rate automatically balances packet transmission interrupts and host
CPU performance. In most cases no manual optimization of the Interrupt Moderation
Rate parameter is required.
In some conditions, video frames from the GigE Vision detector may be transferred to the
host display or memory buffer as data bursts instead of a smooth continuous stream. The
NIC may be over-moderating acquisition interrupts to avoid over-loading the host CPU
with interrupts. If priority is required for acquisition transfers (i.e. a more real-time
system response to the detector transfer) then the moderation rate should be set to
“maximum” by manually adjusting the NIC parameter.
In the end, this is a compromise:
1. Enable interrupt moderation to minimize CPU usage, at the expense of a slight increase
in latency (recommended).
2. Disable interrupt moderation to favor responsiveness of real-time system with a
drawback in CPU usage.
In most situations, extra latency introduced by interrupt moderation is very low and thus
the gain on CPU performance becomes more beneficial.
