Date: Sun, 14 Mar 1999 11:45:21 -0800 From: Amancio Hasty <hasty@rah.star-gate.com> To: Matthew Dillon <dillon@apollo.backplane.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: <199903141945.LAA87562@rah.star-gate.com> In-Reply-To: Your message of "Sun, 14 Mar 1999 11:20:28 PST." <199903141920.LAA93395@apollo.backplane.com>
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If the pci device has the concept of a program store like in the case of a bt848 chipset it is conceivable for dma or internal operations to do a retry. It is a different issue if the network chipset designers chose not to have a programmable dma or process control like in the bt848 . Best Regards, Amancio > > :> 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> > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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