TCP checksum errors on mec0 on an O2

Hi,

I'm running NetBSD 8.1 on a R5000/180 O2 and seeing a lot of stalls and
hangs when using FTP to send files over the mec0 Ethernet interface.
Small files (less than around 4k) transfer successfully, anything much
larger fails. On the receiving machine, the files are truncated at
exactly 2896 bytes.

Using WireShark on a separate machine, to sample the packets on the
wire, I see that the first two packets are sent correctly and the third
packet has a TCP checksum error. Data size in the packets is 1448
bytes, which explains the 2896 bytes at the receiving end. I've had a
look in if_mec.c and I can see the receive checksum routine,
mec_rxcsum, but I don't see the transmit checksum. Is it done by the
MACE chip or is it somewhere else in the code?

George