Re: what does "host bridge" mean?

From: Geir Frode Raanes Sørensen (geirfrs_at_REPLACE.ed.ntnu.no)
Date: 08/11/04 

Date: Wed, 11 Aug 2004 05:34:37 +0000 (UTC)

David Kinsell <kinsell@poboxyz.com> wrote:
: That's the right general idea. More commonly, the implementation only takes
: up part of a chip, such as one of the support chips in an Intel architecture PC,
: or it's just built into the processor, like in the more highly integrated PPC chips.
: But it is indeed a bus conversion from a processor bus to a PCI bus. Lets a
: bus-master PCI card access memory on the other side.
:
:
: "??$?" <??$?@phantom.com> wrote in message news:41193317$0$22718$39cecf19@news.twtelecom.net...
:> I'm sure that people more experienced that I will correct me, but when I was
:> working with PCI, on the platform that I worked with the "host-bridge" was
:> an IC that served as bridge between the PowerPC data bus and the PCI data
:> bus.

Correct. A bridge between the sytem Local Bus and the Peripheral Component
Interconnect (PCI) bus.

But there is more to it - there might be multiple local bus to PCI bridges
in the system. There might even be mulitple PCI buses connected either
transparent (hierarchal) or non-transparent. There might even be completely
different buses in the system, like ISA or VME. All of them require access
to the PCI bus and system memory, otherwise they wouldn't be there in the
first place. Most of them even require bus master privileges. And it is the
responsibility of the 'host bridge' to do the arbitration between the
different contenders for PCI bus time slices. Interrupt steering should
have been here too, but more often than not isn't. 

-- 
  ******************************************************
  Never ever underestimate the power of human stupidity.
  -Robert Anson Heinlein
		GeirFRS@INVALID.and.so.forth
  ******************************************************

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