Re: Peer-to-peer transactions

[Paul Capes <pcapes@ics-ltd.com>]

Hi all,

I too have started looking at peer-to-peer capability of PCI devices, and am
quite confused about how to proceed. The software guys are telling me that there
is no mechanism in the NT operating system that allows this to occur. Can
someone comment?

Francois Barlow wrote:

> Hi,
>
> I'd like to point on a restriction that is fairly new to me, and I'm curious
> to see how known this issue is from the PCI community.
>
> Our applications involve several of our PCI boards to communicate with each
> other (using PCI memory write and memory read transactions).  We notice that
> in some systems, with several of our boards connected in them, it was
> impossible for a PCI master to access a PCI target device located on a
> different PCI bus segment.
>
> As an exemple, the Intel 82860 chipset (Memory Controller Hub) uses 3
> different Hub interfaces to create PCI bus segments in order to accomodate
> several PCI devices.  The MCH is not able to handle PCI transactions between
> two PCI devices that are respectively located behind Hubs A and B.  These
> devices can only communicate with the system memory or with an other PCI
> device located on the same bus segment (some other documented constraints
> exist).  That is, peer-to-peer transactions crossing PCI bus segments is not
> possible in all configurations.
>
> Section 1.5 of the PCI spec (revision 2.3) says that one benefit of the PCI
> local bus is the flexibility that allows "Full multi-master capability
> allowing any PCI master peer-to-perr access to any PCI master/target".
>
> I'd like to have some feedback on this, because I think that we are not the
> only one concerned by this restriction.  I'm also curious to know how many
> systems don't support peer-to-peer transactions.  In a matter-of-fact,
> writting to system memory before requesting the Host to transfer the data to
> the correct PCI device is not a very efficient alternative.
>
> Thank you,
>
> François.
>
> **********************************
> François Barlow
> Asic Design Leader
> Matrox electronic systems
> Imaging department
> tel: 514-685-7230 x2280
> fax: 514-822-6110
> email: fbarlow@matrox.com
> **********************************

--
Paul Capes

Interactive Circuits and Systems Ltd.
5430 Canotek Road
Ottawa, Ontario
Canada K1J 9G2
Tel (613) 749-9241
Fax (613) 749-9461
Email pcapes@ics-ltd.com