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Re: [Xen-devel] Re: debugging Xen in a serial-less environment

To: Christian Tramnitz <chris.ace@xxxxxxx>
Subject: Re: [Xen-devel] Re: debugging Xen in a serial-less environment
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Sat, 07 Mar 2009 01:48:49 -0800
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Christian Tramnitz wrote:
But it seems to be a bit harder to find those dongles. It look like the only model (NET20DC) isn't RoHS compliant which explains why I don't find a place to order them in Eruope. But other than that this seems to be a good long-term alternative to a serial console. I haven't looked at the code for it in the linux kernel but does anyone know if it's required to get all the hcd and usbcore stuff loaded before being able to use the debug port? If not, whats the behaviour of the usb bus (and the debug port) when those drivers are loaded by dom0 subsequently?

It appears that the USB hardware has a special simplified PIO programming mode that is relatively easy to operate without the full USB stack in place. But there's a comment in the Linux code to the effect that you can't keep a debug port early console because the full USB stack will subsequently reset and take over the hardware.

In Xen I'm guessing that means that you'd have to dedicate a USB controller to debug output and prevent dom0 from using it. Which seems a bit inconvenient.


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