Date: Wed, 24 Nov 2004 10:19:25 -0500 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-current@FreeBSD.org Cc: Scott Long <scottl@FreeBSD.org> Subject: Re: Transparent bridges (a. k. a. HUB-to-PCI bridges)? Message-ID: <200411241019.25271.jhb@FreeBSD.org> In-Reply-To: <41A49EF1.8030603@mac.com> References: <200411231226.38172.jkim@niksun.com> <41A49312.5@freebsd.org> <41A49EF1.8030603@mac.com>
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On Wednesday 24 November 2004 09:47 am, Chuck Swiger wrote: > Scott Long wrote: > > Chuck Swiger wrote: > > [ ... ] > > >> A host-PCI bridge is typically part of the "southbridge" chip of > >> modern motherboards; on Intel motherboards this is also called the ICH > >> chip, such as the 82801AA/BA/CA/etc. VIA Southbridges include the > >> VT8233/8235/8237/etc. > > > > Nope. The southbridge typically holds a PCI-ISA bridge. The host-pci > > bridge is usually found in the northbridge part of the chipset. The > > whole point it to bridge the CPU to one or more PCI buses. > > 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", or MCH, connects to the CPU, AGP, RAM, and the > southbridge. > > The "southbridge", or ICH, connects to PCI, ATA, USB, BIOS chip, and the > northbridge. Newer southbridge chips may add integrated LAN, > 1394/Firewire, integrated AC'97 audio, and such via external codec chips > like the VT6103 PHY. The northbridge is the host-pci bridge. It contains a virtual PCI-PCI bridge/bus that represents AGP. The chipset uses a propietary interconnect to the southbridge 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. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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