Date: Wed, 24 Nov 2004 14:19:53 -0700 From: Scott Long <scottl@freebsd.org> To: Charles Swiger <cswiger@mac.com> Cc: freebsd-current@freebsd.org Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? Message-ID: <41A4FAF9.1080704@freebsd.org> In-Reply-To: <0F179BC4-3E3E-11D9-BD47-003065ABFD92@mac.com> References: <200411231226.38172.jkim@niksun.com> <41A49312.5@freebsd.org> <41A49EF1.8030603@mac.com> <200411241019.25271.jhb@FreeBSD.org> <0F179BC4-3E3E-11D9-BD47-003065ABFD92@mac.com>
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Charles Swiger wrote: > 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. > Not a problem. The V-Link and ICH buses are really just high-speed tunnels for PCI. Before their invention, the southbridge was directly connected to the northbridge via PCI. Scott
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