Re: [Xen-users] Where can I find a USB debug cable?

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

Hello,

El 10/07/15 a les 11.12, Ian Campbell ha escrit:
> On Thu, 2015-07-09 at 19:45 +0200, Manfred Haertel, DB3HM wrote:
>> I would like to use the Xen serial console, but on a computer which does 
>> not have a serial device.
>>
>> So I have to use the so-called USB debugging port (console=dbgp). The 
>> USB controller in my system seems to support this.
>>
>> But where do I find an USB cable to connect my computer to another one 
>> via USB?
>>
>> Most documentations refer to a small device called NET20DC, to which you 
>> can connect both computers via USB. Unfortunately, this device doesn't 
>> seem to be available anymore.
> 
> Indeed, a while back I searched long and hard for such a thing and
> didn't come up with anything, I concluded that they were either
> fictional, ancient and unavailable or something one needed to build for
> oneself with a soldering iron :-/

The only one of this kind of devices that's available right now it's
AMIDebug RX
(http://www.ami.com/products/bios-uefi-tools-and-utilities/amidebug-rx/)
which does a bunch of other things apart from Host-to-Host debugging,
and more important, it costs 500$ per unit.

> I just had another look and things seem more promising, the "Net chip
> USB debug link" in
> https://www.kernel.org/doc/Documentation/x86/earlyprintk.txt remains
> dead but I found https://github.com/avivgr/teensy_debugdev and
> http://blogs.msdn.com/b/usbcoreblog/archive/2010/10/25/setting-up-kernel-debugging-with-usb-2-0.aspx
>  
> 
> Which lead me to google "usb debug cable" and find things such as:
> http://www.datapro.net/products/usb-3-0-super-speed-a-a-debugging-cable.html
> and a bunch of ones which don't look right (mostly extension cables or
> TTL/serial on one end).

AFAIK this only works if you have a XHCI (USB 3.0) debug port, it's not
going to work with the more common EHCI (USB 2.0) debug ports. And I've
been told XHCI debug ports are not that common even on new hardware.

> I have no idea if that datapro thing is actually the right thing, but it
> looks promising...
> 
>> Is there another device, which is still available and is known to work?

IMHO the only realistic option (unless you want to spend 500$) is to
build one yourself, I've found the following wiki page with _some_
information, although I have not tried to follow it myself:

http://www.coreboot.org/DIY_EHCI_debug_dongle

Roger.


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