Other ways for working with interconnect between MPU and MCU

Hi all! Can anybody give advice about other methods of working with interconnect between MPU and MCU. I saw example working with RPMsg, but in this case we have a problem with memory, because we need a big buff in MCU for data. Now we trying to use DDR SDRAM, but STM doesn't recommended to use it. So, maybe anybody faced with it or solved it?