From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MLIkt-0007ti-KU for qemu-devel@nongnu.org; Mon, 29 Jun 2009 11:26:52 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MLIko-0007rf-KM for qemu-devel@nongnu.org; Mon, 29 Jun 2009 11:26:51 -0400 Received: from [199.232.76.173] (port=51641 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MLIko-0007rJ-9p for qemu-devel@nongnu.org; Mon, 29 Jun 2009 11:26:46 -0400 Received: from mail-pz0-f185.google.com ([209.85.222.185]:55411) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MLIkn-0006Va-Ir for qemu-devel@nongnu.org; Mon, 29 Jun 2009 11:26:45 -0400 Received: by pzk15 with SMTP id 15so2171330pzk.4 for ; Mon, 29 Jun 2009 08:26:44 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4A48CE67.9070705@redhat.com> References: <1246262725-23825-1-git-send-email-jljusten@gmail.com> <4A48C5F5.6030402@codemonkey.ws> <4A48CE67.9070705@redhat.com> Date: Mon, 29 Jun 2009 08:26:41 -0700 Message-ID: <2a50f7880906290826t4128b11dyc68a36fd01e8208c@mail.gmail.com> Subject: Re: [Qemu-devel] [PATCH] Implement PC port80 debug register. From: Jordan Justen Content-Type: multipart/alternative; boundary=00504502c83f4c7439046d7e51d9 List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: qemu-devel@nongnu.org --00504502c83f4c7439046d7e51d9 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Avi, Well, I am not sure if this it globally the case for PC motherboards, but in my experience, it has been read/write. 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. -Jordan On Mon, Jun 29, 2009 at 7:23 AM, Avi Kivity wrote: > On 06/29/2009 04:47 PM, Anthony Liguori wrote: > >> Jordan Justen wrote: >> >>> From: jljusten >>> >>> In PC systems, the byte I/O port 0x80 is commonly made into a >>> read/write byte. BIOS and/or system software will often use >>> it as a simple checkpoint marker. >>> >> >> What software does this? Typically, port80 is used as an IO delay >> mechanism. I'm not aware of it being used to read/write arbitrary data. >> >> > It's often used in BIOS code. There used to be seven-segment cards you'd > plug into a computer that would show you port 80 in real time. I think it's > a write-only port, though. > > -- > error compiling committee.c: too many arguments to function > > --00504502c83f4c7439046d7e51d9 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Avi,

Well, I am not sure if this it globally the case for PC motherb= oards, but in my experience, it has been read/write.

At least for a = system such as qemu, it make it difficult to use the port80 checkpoint of s= oftware without being able to read the last value written.

-Jordan

On Mon, Jun 29, 2009 at 7:23 = AM, Avi Kivity <avi@= redhat.com> wrote:
On 06/29/2009 04:47 PM, Anthony Liguori w= rote:
Jordan Justen wrote:
From: jljusten <jljusten@jljusten-laptop.(none)>

In PC systems, the byte I/O port 0x80 is commonly made into a
read/write byte. =A0BIOS and/or system software will often use
it as a simple checkpoint marker.

What software does this? =A0Typically, port80 is used as an IO delay mechan= ism. =A0I'm not aware of it being used to read/write arbitrary data.

It's often used in BIOS code. =A0There used to be seven-segment cards y= ou'd plug into a computer that would show you port 80 in real time. =A0= I think it's a write-only port, though.

--
error compiling committee.c: too many arguments to function


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