Avi,<br><br>Well, I am not sure if this it globally the case for PC motherboards, but in my experience, it has been read/write.<br><br>At least for a system such as qemu, it make it difficult to use the port80 checkpoint of software without being able to read the last value written.<br>
<br>-Jordan<br><br><div class="gmail_quote">On Mon, Jun 29, 2009 at 7:23 AM, Avi Kivity <span dir="ltr">&lt;<a href="mailto:avi@redhat.com">avi@redhat.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div><div></div><div class="h5">On 06/29/2009 04:47 PM, Anthony Liguori wrote:<br>
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Jordan Justen wrote:<br>
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From: jljusten &lt;jljusten@jljusten-laptop.(none)&gt;<br>
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In PC systems, the byte I/O port 0x80 is commonly made into a<br>
read/write byte.  BIOS and/or system software will often use<br>
it as a simple checkpoint marker.<br>
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What software does this?  Typically, port80 is used as an IO delay mechanism.  I&#39;m not aware of it being used to read/write arbitrary data.<br>
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It&#39;s often used in BIOS code.  There used to be seven-segment cards you&#39;d plug into a computer that would show you port 80 in real time.  I think it&#39;s a write-only port, though.<br><font color="#888888">
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-- <br>
error compiling committee.c: too many arguments to function<br>
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