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Date: Sat, 02 Jan 2010 10:56:29 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: [Qemu-devel] [PATCH] debugcon: support for debugging consoles
	(e.g. Bochs port 0xe9)
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To: Kevin O'Connor <kevin@koconnor.net>
Cc: qemu-devel@nongnu.org

On 01/02/2010 09:53 AM, Kevin O'Connor wrote:
> On Fri, Jan 01, 2010 at 07:02:59PM -0800, H. Peter Anvin wrote:
>> On 12/30/2009 08:49 AM, Kevin O'Connor wrote:
>>> SeaBIOS writes debugging info to port 0x0402.  Unfortunately, qemu has
>>> to be recompiled in order to display this info.  Will your patch
>>> enable one to get at the 0x0402 data without recompiling?
>>
>> Incidentally, it's somewhat unusual choice of ports... port 0x80 is the
>> normal port for BIOSes to display debugging information on.
> 
> Port 0x0402 is a carry over from Bochs bios.
> 
> Port 0x80 isn't generally used to emit a stream of ascii data, and it
> can be used by other programs besides the bios.  I'd guess that's why
> Bochs chose a different port.
> 
> -Kevin

Makes sense.  Either way, it works with my patch looking something like:

	-chardev stdio,id=seabios \
	-device isa-debugcon,iobase=0x402,chardev=seabios

... should do the job.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.