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Re: ea2468 Ethernet overrun

On Wed, Jun 03, 2009 at 05:43:04PM +0400, Nikolay Marusov wrote:
> Hello!
> I am playing with Embedded Artists LPC2468-16 OEM Board.
> Has anybody encounetered with a problem of TX overrun while
> transmitting Ethernet packets?
> Device works pretty well at 10Mbit/s but regullarly drops packet when
> transmitting at 100Mbit/s.
> What may be the cause?

Is it an overrun or an underrun?

I've seen underrun problems before in an intel chipset. The problem
was that the DMA would start transferring the packet from the host RAM
to the ethernet chipset. When X bytes of the packet had arrived at the
ethernet, the ethernet started sending them on the wire. Under heavy
memory load, the DMA was slower than the Ethernet sending bytes on the
wire, and with long packets the ethernet chip would empty its buffer
and then throw an underrun error. I had the change the Ethernet
chipset to have a bigger X so it had more buffered bytes before it
started sending them to the wire.


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