[coreboot] USB debug cables and emulation

Joseph Smith joe at settoplinux.org
Fri Jun 27 19:15:32 CEST 2008

On Fri, 27 Jun 2008 17:04:29 +0200, Peter Stuge <peter at stuge.se> wrote:
> 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:
> http://www.usb.org/developers/docs/
Thanks for the tip Peter, I will do some reading.
>> 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.
> http://www.plxtech.com/products/net2000/
Is the datasheet publicly available?
>> I'll bet anyone all the electrical components inside that little
>> box can be purchased for less than 20 dollars.
> In which quantity?
Maybe when I figure it out, I will buy a big batch and sell them cheaper to
those interested:-)
>> 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.
So is there some kind of memory device with the "microcontroller software"?
Like a eprom or eeprom??
> 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!
Good, than maybe this little side project will work out great for everyone.
Maybe I will learn so much about USB I will be able contribute else where;
like filo, GRUB2, and LegacyBIOS :-)
> 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! :)
Also, another question about this topic. I read somewhere someone was
working on a Linux Kernel driver for the NET20DC for the host PC. Did this
ever implimented? Can you use the NET20DC in linux on a host PC? If so, how
does it work?

Joseph Smith

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