about the Tulip & Intel PRO 1000

[Giorgio Calarco]

Hi,

I 'm reading your paper "programming language optimizations
for modular router configurations" and there are some details
which I cannot understand, probably due to my poor knowledge
of how the hardware platform works...
I try to explain what I think I have understood, plese correct
me if I mistake... I refer to paragraph 8.4 - PCI limitations.

You wrote that packets can be dropped on the receving
tulip card because the internal buffer is full or because the NIC
is not able to fetch a ready DMA descriptor etc etc.
My first question is: with DMA you mean the "direct memory access" ?
If so, are you transferring the packets from the NIC to memory
making the tulip card to be the PCI bus master and
programming it to transfer the packets without
involving the CPU ? If not, how the transferral works ?

If what I've thought is true, I have a second question...
about the Intel PRO 1000.
I'm reading that this can be slower than the tulip card because the
packets are transferred via PIO. Is there a reason for this ?
I mean, the Intel PRO1000 is unable to become the PCI
bus master and the only way to move the packets around
needs the CPU to be involved (being it the bus master)?
Or is this choice due to other reasons ?


Thanks in advance for your answers

giorgio




Ing. Giorgio Calarco
DEIS - Università di Bologna
Viale Risorgimento, 2 40136 Bologna - Italy
Tel: 051 2093776 Fax: 051 2093053
E-mail: gcalarco at deis.unibo.it
PGP: http://www.deis.unibo.it/GCalarco/Giorgio_Calarco.asc