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Date: Tue, 30 Jun 2009 01:18:41 +0200
From: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
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Subject: Re: [Qemu-devel] [PATCH] Implement PC port80 debug register.
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To: Avi Kivity <avi@redhat.com>
Cc: Jordan Justen <jljusten@gmail.com>, qemu-devel@nongnu.org

On 29.06.2009 17:36, Avi Kivity wrote:
> On 06/29/2009 06:26 PM, Jordan Justen wrote:
>> Well, I am not sure if this it globally the case for PC motherboards,
>> but in my experience, it has been read/write.
>
> Why would software ever need to read it?  You want a monitor command
> so the user can read it.  I don't recall ever seeing a read of port 80
> (I don't have any objections to that though).

AFAIK some Linux versions use port 0x80 reads (instead of writes) for
some delays (grep for REALLY_SLOW_IO) because some hardware vendors
started abusing writes to port 0x80 for communication with embedded
controllers.

Regards,
Carl-Daniel

-- 
http://www.hailfinger.org/