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Date:      Wed, 21 Jul 2004 15:59:01 +0100
From:      Doug Rabson <dfr@nlsystems.com>
To:        Andrew Gallatin <gallatin@cs.duke.edu>
Cc:        freebsd-current@freebsd.org
Subject:   Re: Excellent job on the firewire support!
Message-ID:  <1090421941.7114.26.camel@builder02.qubesoft.com>
In-Reply-To: <16638.32914.509773.486468@grasshopper.cs.duke.edu>
References:  <16634.47272.768935.436137@grasshopper.cs.duke.edu> <200407182039.10773.dfr@nlsystems.com> <16634.54674.966908.540880@grasshopper.cs.duke.edu> <200407182104.53221.dfr@nlsystems.com> <16638.32914.509773.486468@grasshopper.cs.duke.edu>

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On Wed, 2004-07-21 at 15:41, Andrew Gallatin wrote:
> Doug Rabson writes:
>  > Actually thats the only downside of dcons. It doesn't cut in until the 
>  > firewire controller attaches. It relies on the fact that the fwohci 
>  > driver allows access to physical memory from any node on the bus 
>  > (implemeted in hardware so you can examine the memory of a hung 
>  > machine). The dconschat program uses this feature to access the dcons 
>  > ring buffers in the target machine.
> 
> Does remote access to physical memory require dcons to be loaded
> on the target?

No. The remote access to physical memory is a hardware-implemented
feature of the firewire ohci hardware. Its enabled in fwohci_attach().
In the long term, I would like to restrict this a bit but right now all
you have to have is fwohci loaded on the target machine.

> 
> If no, assuming I had a Windows or Linux box on the firewire bus, would it be
> possible to access physical memory from a different OS?

Windows XP has some kind of firewire debug driver that you might have to
load (I haven't read the docs on that). I don't think the linux driver
enables physical access by default but it would be easy to hack it in
(just write all ones to the right fwohci register).





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