about the Tulip & Intel PRO 1000

[Robert Morris]

Giorgio,

Yes, by DMA we mean direct memory access. The Tulip does transfer
packets to/from memory without direct CPU intervention.

The Intel Pro 1000 also uses DMA, and is generally similar to the
Tulip. However, the CPU must use one PIO instruction per batch of
packets to notify the Pro 1000 that there is new work for it to do.

Robert

> From: "Giorgio Calarco" <gcalarco at deis.unibo.it>
> To: <click at amsterdam.lcs.mit.edu>
> Subject: about the Tulip & Intel PRO 1000
> Date: Mon, 14 Apr 2003 11:52:09 +0200
> Organization: DEIS
> 
> 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
> 
>