Hello,
You can use MCC, which uses shared SRAM, for communication between the two cores. For more information about MCC, you can see the user guide here:
Vybrid MCC User Guide For MCC Version 1.0 | Timesys Embedded Linux
However, peripheral isolation is currently not graceful between M4 and A5 - peripherals used in M4 and A5 are hardcoded in the Linux kernel and MQX source code. For complete isolation, you will need to customize the Linux kernel / mqx configuration and sources to achieve this.
Thanks, and let me know if you have any questions.
Timesys Support