Multi master bus overload

Hi Cameron,  I think the master communication that happens in the background should be fine.  Where you will need to be careful is using the APPOUT channels to relay information between the masters.  An APPOUT channel uses a whole CAN frame for each piece of information regardless of size. (If it is one bit or 4 bytes it will use a whole CAN frame.)  The logic behind an APPOUT using a whole CAN frame is that they are set up to handle SIL2 CAN messages between two functional safety masters.  With that setup, part of the message uses data to ensure the message meets the safety requirements. 

A more efficient way to handle this is to use J1939 or generic CAN frames.  This will allow you to set up the frame output channels with multiple pieces of information in one frame and therefore reduce the number of CAN frames on the bus.  It will also allow you to potentially place the CAN traffic on multiple buses to help reduce load on any one bus.  Using a master bus, the information is placed on one particular bus.

In addition to Kerry's comments, have you also considered using XC43s instead of MC43s to reduce application complexity?

I originally started that way but due to the need of MD3's i am not able to use Design 6. Design 5 doesn't allow the XC4x's

Have you considered the MD4-5 as an alternative to the MD3 ? 

In particular the new MD4-5 M19 that is more cost effective than the original MD4-5-T1E2. 

The reason the MD3 isn't available on version 6 together with the new XC4x expansions is that the MD3 is getting mature. Even though MD3 isn't in phase out yet and still have several years to live, we don't want to encourage the use of an old product in new system designs.