Date: Sun, 14 Mar 1999 11:20:28 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Amancio Hasty <hasty@rah.star-gate.com> Cc: Wes Peters <wes@softweyr.com>, Cory Kempf <ckempf@enigami.com>, Bill Paul <wpaul@skynet.ctr.columbia.edu>, freebsd-hackers@FreeBSD.ORG Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <199903141920.LAA93395@apollo.backplane.com> References: <199903140927.BAA85633@rah.star-gate.com>
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:> cannot be done. So routing a single packet requires the data to flow
:> over the PCI bus twice. The 132 MBytes/sec become 66 MBytes/sec right
:> off the bat.
:
:I am not sure that I can follow you here . Most PCI cards which are capable of
:doing dma to the host system's memory can do card - to - card transfer
:;however,
:the target "card" most be able to use the stored data in the case of a network
:card it must have memory to receive the pack or a very elaborate protocol
:to accept short dma bursts which it can then process.
:
:
: Amancio
You can always do a card-to-card transfer, but since most modern network
cards do *NOT* have on-card memory doing a card-to-card transfer typically
doesn't work. For example, if the destination card hits a collision/retry,
the source card's FIFO can overflow.
It just doesn't work.
Using a card as a DMA destination only works well for cards that map
memory, such as a video card.
-Matt
Matthew Dillon
<dillon@backplane.com>
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