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Re: [Qemu-discuss] QEMU and reboots via 0xcf9

From: Jakob Bohm
Subject: Re: [Qemu-discuss] QEMU and reboots via 0xcf9
Date: Fri, 28 Dec 2012 21:46:22 +0100
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On 12/28/2012 7:36 PM, John Floren wrote:
On Fri, Dec 28, 2012 at 12:57 AM, Dipanjan Das
<address@hidden> wrote:

On 28 December 2012 00:03, Jakob Bohm <address@hidden> wrote:
On 12/27/2012 7:08 PM, John Floren wrote:
I'm working on an OS kernel that currently reboots by writing 0x02,
then 0x06 to port 0xcf9. This seems to work fine for real hardware,
but I have not been able to make it work in QEMU. Before I go digging
through the QEMU source to try and verify one way or another, I
thought I'd ask here: Can I use 0xcf9 to reboot on QEMU?

Try the technique documented here.

Well, we still don't know if QEMU supports 0xcf9, although my own
shallow explorations of the code indicate that it does not. Maybe I
should ask the dev list?

As I said earlier, we had avoided using the 8042 because it's not a
sure bet that the hardware we'll be using will even include an 8042,
while it's much more likely that modern hardware will support 0xcf9
reboots. It does work on QEMU, but I don't know what it'll do on a
machine without an 8042.


Note: As I have explained in private mail, port 0x61 really has nothing
to do with the 8042 keyboard controller, it just happened to be
integrated in the same chip on the old PC/ATmotherboard.

On modern chipsets where all the classic (and some not so classic) i/o
devices are bundled together in one or two VLSI chips, port 0x61 should
be considered a separate device unrelated to the legacy keyboard/mouse
controller chip.  If anything, it belongs in either the audio (PC
speaker) or the bus controller areas of the chipset (because it controls
3 functions: PC speaker beeps, NMI interrupt routing and the reset


Jakob Bohm, CIO, Partner, WiseMo A/S.  http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark.  Direct +45 31 13 16 10
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