User Manual, Rev 01
19
Teledyne DALSA
Rad-icon 2329 GigE Detector
For further information regarding packet settings and network card optimization
please refer to the document ‘Network Imaging Package for Sapera LT Optimization
Guide’.
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.
Receive Buffers
