Date: Wed, 24 Nov 2004 12:27:04 -0500 From: Charles Swiger <cswiger@mac.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Scott Long <scottl@FreeBSD.org> Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? Message-ID: <0F179BC4-3E3E-11D9-BD47-003065ABFD92@mac.com> In-Reply-To: <200411241019.25271.jhb@FreeBSD.org> References: <200411231226.38172.jkim@niksun.com> <41A49312.5@freebsd.org> <41A49EF1.8030603@mac.com> <200411241019.25271.jhb@FreeBSD.org>
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On Nov 24, 2004, at 10:19 AM, John Baldwin wrote: >> I've been wrong before, but please double-check diagrams like: >> >> http://www.intel.com/design/chipsets/850/pix/850_800.gif >> http://www.viatech.com/en/products/chipsets/p4-series/pt880/ [ ... ] > The northbridge is the host-pci bridge. It contains a virtual PCI-PCI > bridge/bus that represents AGP. Agreed, although AGP is something of a special case. > The chipset uses a propietary interconnect to the southbridge... Such as VIA's V-link. > ...such that the devices the north and south bridges connect > to show up as one pci bus (bus 0). You could build a system without a > southbridge (just PCI-X bridges or some such) and it would still have a > host-pci bridge. You and Scott are correct. pciconf claims that something like a 440BX northbridge (82443BX) contains both a HOST-PCI and a PCI-PCI bridge, whereas the PIIX4 southbridge (82371AB) has a PCI-ISA bridge, as well as ATA and the other things I'd mentioned. I apologize if I confused the person I was trying to answer. -- -Chuck
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