Maximum ethernet speed available with NiosII + Linux

See my thread on this here: http://www.alteraforum.com/forum/showthread.php?t=18934

There's a link or two to other useful threads there too.

So far ethernet performance with a gigabit PHY (DP83865) can best be described as disappointing. I haven't been able to get it to work correctly at gigabit speed, so my results should be comparable to the DP83848.

I am getting at best 38Mbit/s UDP with 1KB messages and 30Mbit/s TCP with the following tweaks:

- altera_tse.c (SLS) driver for the altera TSE MAC

- 32KB processor caches

- a bunch of network related kernel functions in SSRAM instead of DDR DRAM

- no cache burst

- MMU (similar results without it)

I am also seeing some unexplained dropped packets.

Note that at least one other person in the thread has been able to get hundreds of Mbit/s with a similar setup, though they weren't using Linux.