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    |   xen-devel
Re: [Xen-devel] Re: debugging Xen in a serial-less environment 
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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. 
   J
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