Date: Mon, 6 Dec 1999 11:10:33 -0600 From: kvandel <kvandel@cs.duke.edu> To: Mike Smith <msmith@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: fxp, xl driver question .. (routing)(SOLVED) Message-ID: <99120611312500.00860@wookie.vandelden.com> In-Reply-To: <199912060813.AAA01499@mass.cdrom.com> References: <199912060813.AAA01499@mass.cdrom.com>
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Mike- > I should have summarised this by saying: Correct use of the latency > timer will shorten your DMA bursts for you when necessary, giving you the > best of both worlds. When it's safe to run a long burst, you will. When > you need to push a device off the bus, that will happen too. After re-reading the PCI System Architecture section.. you are correct. The Text: If the current master has exhausted its LT, still has its GNT# and has not yet completed its burst transfer, it may retain ownership of the bus and continue to burst data until either: a. it completes its overall burst transfer b. its GNT# is removed by the arbiter In the latter case, the current master is permitted to complete one or more data transfer and must then yield the bus. My misunderstanding: From the wording in the text, it is ambiguous as whether the a "data transfer" is a frame(one adress cycle + multiple data cycles), or a data cycle. > And the obvious extension to the "worst case" calculation is that if you > have N master devices each with a latency timer of X, your worst-case > timing for CPU access to a device is (N * X) + (N * arb overhead), just > in case that wasn't clear. Much better... thanks, kurt > > -- > \\ Give a man a fish, and you feed him for a day. \\ Mike Smith > \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org > \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com -- uname -a > Linux wookie.vandelden.com 2.2.13 #1 < To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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