Subject: Re: Fwd: Located problem in pcn driver...
To: John Gordon <>
From: Kamal R Prasad <>
List: tech-kern
Date: 04/21/2003 06:07:38

Kamal R. Prasad
AIX Support & Test, IBM India Software Labs
Golden Enclave, Airport Road, Bangalore-560017, India
Phone : +91-80-5094963,  Internal Ext   : 2963


> The address used for DMA is physical memory address. Do you say
> that PCI and CPU see different physical memory adresses? That's
> quite weird.

>PC programmers will wonder why it is all so complex; those of us that have
>PPC systems for a while are used to it (I've been working with embedded
>devices now since the mid-1990's starting with an MVME-1604 system - and
>have a PCI-VME bridge to add another layer of trsnslations ;-). It
>comes down to the fact that PCI is an alien bus for PPC, and the bridge
>try to make it fit into the PPC world and still work.

PCI is the standard bus for POWER4-based systems. there is a logic in place
that looks at an address to decide if it(load/store) is meant for I/O
device or memory and probably bypasses cache as a result for I/O operations
without the volatile keyword being used.


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