[coreboot] USB debug cables and emulation

Peter Stuge peter at stuge.se
Fri Jun 27 17:04:29 CEST 2008

On Fri, Jun 27, 2008 at 10:28:07AM -0400, Joseph Smith wrote:
> Well, as some of you may know I am a bit of a hardware hacker.
> That's what brought me to coreboot in the first place.

That does not get you too far when it comes to USB, which has
several layers of protocol. Please do look into the USB spec:

> As soon as my budget will allow it I am going to get a NET20DC, pop
> open the little box, and exploit the hardware.

You will find two PLX Technology NET 2270 chips and a microcontroller
(I'm not sure which micro it was, maybe Ubicom SX) responsible for
configuration and data flow control in the NET 2270s.


> I'll bet anyone all the electrical components inside that little
> box can be purchased for less than 20 dollars.

In which quantity?

> I'm also going to get one of the Host-to-Host Cables mentioned
> above (you can find them on eBay for less than 10 dollars) and see
> how hard it would be to convert one.

This will not be a hardware exercise. I imagine the CDC cables are
constructed similar to the NET20DC, but the microcontroller software
within will be quite different.

So, you will have to reverse engineer the microcontroller software,
and re-engineering a software that does what the NET20DC does.

Assuming of course that the USB chips in the cheapo CDC cables are
as flexible as NET 2270 - which I doubt.

> Once I start this little side project, is it ok to setup a wiki
> page on coreboot, or could there be liability issues? Otherwise I
> will just post a discrete page on my site.

You will be learning a lot about USB - which I think is a great idea!
I like USB a lot. I strongly recommend reading the USB spec. It is a
few hundred pages, but you can skim some parts. It is really required
reading. I think USB is well-designed and far too few know it well -
so go for it! :)

All I'm saying is don't expect it to be about hardware.


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