Subject: Re: Multiple busses of the same kind
To: Wojciech Puchar <>
From: Nathan J. Williams <nathanw@MIT.EDU>
List: tech-kern
Date: 07/30/2001 12:17:16
Wojciech Puchar <> writes:

> > > The problem is basically that the ISA bus is attached twice because he
> > > has two pcib's: one in his laptop, the other provided by his base
> > > station.
> >
> > Err... do those isa bi (busses?) share their address space?
> can pci to isa bridges be programmed only to map isa address/port space
> from 0?
> if not we can have as much ISA busses as we need.

In theory this could be done.

In practice, I've never seen a PCI-ISA bridge that did it; I conclude
that it's not a feature anyone wants. PCI-ISA bridges usually just do
untranslated subtractive decoding of memory addresses below 16M and
I/O addresses below 64k, plus decoding for whatever their onboard
devices are.

(Note that there isn't a standard for PCI-ISA bridges to follow, so
any "interesting" programming of it is specific to that model, like
the scatter-gather DMA support on the Intel 82378ZB)

        - Nathan