So this is a single network stack with 2 network interfaces, each assigned a different IP address, talking between the interfaces. This means that the stack is both servicing the end of transmission of the outbound Ethernet frame on one interface and the end of reception on the other interface at roughly the same time. It also is why you have to assign the interface explicitly, otherwise the stack would most likely bypass the Ethernet. I’ve not tried this on FreeRTOS either with lwip or FreeRTOS+TCP, so I don’t know if it leads to any boundary conditions.
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