[Xenomai] Mysterious Mode Switches (Xenomai

Robbert van der Bijl rvanderbijl at seuratech.com
Thu Jun 15 01:51:40 CEST 2017


I'm fairly new when it comes to Linux & Xenomai, but I've been able to
successfully put together the majority of our fairly large application on
our Delta Tau PMAC board (PowerPC 465, dual core) in C++ so far.

The one thing that stumps me though, is the mode switches that happen with
certain memory accesses.

Take this chunk of code for instance:
for (int i=0; i<10000; i++)
   memset(m_pClientSendData+(32*i), 0, 32);

This does NOT cause mode switches when run on a chunk of memory that's been

However, this code DOES cause a mode switch (same memory):
memset(m_pClientSendData, 0, 320000);

The for loop is obviously crazy slow compared to the single memset and not
very practical. But I'm at a loss to explain this behavior. Similar
problems with memcpy as well.

Bottom line, what I'm trying to accomplish is getting around 400k of shared
memory pumped out through a pipe to a TCP/IP task that runs in secondary
mode only, as to avoid having the main task flip back and forth between
primary and secondary modes. I tried to do this with just plain shared
memory initially, but then found out that the mutexes I was using would
force my TCP/IP thread into primary mode when I grabbed the mutex....

Does anyone have any ideas?


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