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TMS320F28386D: lwIP C2000WARE, Jumbo frames exceeding ≈2243bytes not working

Henrik Omberg
Prodigy 20 points

Part Number: TMS320F28386D

As the titel says i have trouble getting jumbo frames working for frames exceeding around 2243 bytes. In the end i want to send jumbo frames with a payload of around 5200 bytes. So i have increased MTU sizes to 5632 bytes. Jumbo packet enable bit and Jabber Disable bit are both set in MAC_Configuration Register. Lwip heap has been increased to 34k, i need to fill up and send 3 packets of 5200 bytes and then while those are transmitted fill upp another 3 frames, ((5200 * 3) * 2) = 31200 bytes.

The following happens:

Sending frame with payload of 2201 bytes works without any problems. The packets is recieved by WireShark and is filled with correct data.

Adding an extra 18 bytes to payload, trying to send the new frame with 2219 bytes of payload -> Nothing is recieved by WireShark.

I have debugged my software and followed the code all the way through the stack and it looks like everything works.

I'm not sure if there are any boundary problems in the RAM, anyways the Payload buffer  in pbuf starts at address 0x20001840, pretty much in the middle of the S0 RAM.

Also tried changing ETHTYPE to ETHTYPE_JUMBO. This only changed the information in the headers, limit was the same.

Can anyone figure out what the problem is? Why around 2243-2261 bytes?

Kind Regards

Henrik Omberg