Shad-o-Scan 3001/4501 User Manual (Draft)
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Teledyne DALSA
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 5Gbit 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 5GigE 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
Under certain conditions the host PC system CPU may be busy with tasks other than the
imaging application. Incoming image packets remain in the PC memory allocated to store
packets instead of immediately being copied into the image buffer. By increasing the
number of NIC (network interface card) receive buffers, more incoming image packets
can be stored by the NIC before it must start discarding them. This provides more time
for the PC to switch tasks and move image packets to the image buffer.
Not all network boards allow increases to their receive buffer count. Among those that
do, different versions will have different maximum receive descriptor values.
We recommend
increasing the receive buffer size to the maximum permitted
by the
network card, in order to provide more buffering capacity when needed.
