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SubjectRe: RFC: Devices, buses and hotplug
On Mon, 7 Jun 1999, Roger Gammans wrote:
> In article <199906061910.MAA30421@pizda.davem.net>, David S. Miller
> <davem@redhat.com> writes
> > Anyway... one question. Who does the byte swapping, the host CPU
> > or the peripheral?
> >
> > If the answer is 'host CPU', then my response is I can write clean
> > code that is faster because it takes advantage of big endian
> > peripheral support.
> >
> >Nope, the host CPU does it, but at _ZERO_ cost. You have two ways
> >usually to get it done:
> >
> >1) Load/Store instruction attributes:
> >
> >2) MMU translations
>
> Erm. There is a third way it could be done. I don't know about any
> specific implementations but the Backplane/bus bridge could implement
> byte swapping merely by the way the data lines are connected.
>
> If I had this problem and was building a motherboard, I would seriously
> consider going this route, unless there was a good reason not to.
>
> Judging by the rest of this thread I assume no-one does it, which is a
> shame. But I suppose if endian-ness was never specified.... sigh.

There are: some Amiga video boards use little endian PCI video chips connected
through a hardware byteswapping Zorro<->PCI FPGA.

Greetings,

Geert

--
Geert Uytterhoeven Geert.Uytterhoeven@cs.kuleuven.ac.be
Wavelets, Linux/{m68k~Amiga,PPC~CHRP} http://www.cs.kuleuven.ac.be/~geert/
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium


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