User manual

Transferring Data Using Communication Blocks
33002479 06 07/2008 127
4.1 Communications Issues
Overloaded Network
Overview If a NOE771xx is used to run in a 100Mb/s Ethernet and a persistent overloaded
network occurs, the NOE771 may go into Kernel mode. This could the cause the
primary CPU to STOP.
Example An example of a persistent overloaded network would be when two ports of an
Ethernet switch are linked to each other: this would be seen by all Ethernet nodes
connected to the sub-network and result in a massive overloaded network -
something that should not occur on properly configured network.
Impact on CPU In order to serve the backplane communication, the NOE has direct access (DMA)
to the memory of the CPU module. Therefore, if the NOE goes into Kernel mode
while accessing the CPU, this may have an impact on the CPU behavior. In rare
cases, it can even cause the Primary CPU to STOP.
Note: Broadcasts and especially ARPs, are part of standard Ethernet traffic and
will have no adverse effects on a NOE. Even "small" storms that take up to 5% of
the basic network traffic over short periods (from several seconds to 2-3 minutes)
would not overload the NOE. It is only the massive and enduring overloaded
network (such as those created by a looped nework cable) that can cause
problems of the HSBY system with NOEs.