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LWIP Stack UDP Large Packet Size External SRAM Problem

Question asked by la_greca.emilio on Aug 28, 2015
Ok so I have a UDP echo server, the requirement being able to echo UDP packets up to 65499 bytes in size.  Test software starts at small packet size increasing the size by one byte , transmitting and expecting the packet to be echoed back. 

After some tweaking size of packet echoed is limited to 59192 bytes using a PBUF_POOL_SIZE of 40 and PBUF_POOL_BUFSIZE of 1514.  Now if PBUF_POOL_SIZE is increased any more than 40 the test fails early in the sequence at a very small packet size (<256 bytes) - Do not know why, maybe someone can help me understand why this is so???

When moving the the PBUF_POOL to external SRAM the packet size is always limited to a maximum of 8872 bytes (1472 x 6) consistently.  I can increase PBUF_POOL_SIZE beyond 40 this time but the test always fails at 8872 bytes - Would anyone know why??

I thought that maybe the ext SRAM interface was not right so I verified its operation with some test code.

Thanks Emilio