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Date: Mon, 09 May 2011 17:21:13 -0600
From: Peter Grehan <grehan@freebsd.org>
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To: Julian Elischer <julian@freebsd.org>, current@freebsd.org
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Subject: Re: firewire debugging
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Hi Julian,

> does anyone know if there is a limitation on firewire debugging on a
> machine with > 4GB or memory?

  I don't know of any Firewire cards that support physical access 
*above* 4GB. They may exist.

  For instance, the (last?) Texas Instruments PCIe 1394a/b chip, the 
XIO2213B, has the following text in it's data sheet -

 >The physical upper bound register is an optional register and is
 >not implemented.

  .. and this is the firewire OHCI register that contains the upper 16 
bits of the architected 48-bit physical address.

  So, you can probably use it for some form of amd64 kernel debug since 
kernel txt/data/bss is < 4G, but accessing anything above 4G won't work.

later,

Peter.