[coreboot] USB debug cables and emulation

Peter Stuge peter at stuge.se
Thu Jul 3 22:21:30 CEST 2008

On Thu, Jul 03, 2008 at 03:42:05PM -0400, Joseph Smith wrote:
> > Manufacturing electronics is VERY expensive, and I think the concern
> > is that you will either be spending ridiculous $$ or be forced to
> > shut down the project before finish, and that either would be a high
> > price for whatever knowledge has been gained.
> > 
> > USB Debug Devices aren't the best target for learning USB in general
> > because the devices need to do some tricks here and there, and thus
> > require high end function controllers that can perform.
> So everyone is just telling me I should give up???

I'm not. :) If you want to spend a lot of time learning about USB I
am all for it! Once you've gotten your first device to work and know
all the twisty passages of the device firmware, it will be alot
easier to adapt it so that it's a debug device instead.

> I wonder how many times OLPC herd that???

Probably many! They persisted, and I bet they did not have the same
motivation as you; education of self and hack credits.

> Ok then I will just give up and go buy a Net20DC :-(

You will not be able to DIY for lower cost, and I say it will take
half a year or more to finish because USB is so complex.

If the goal is to further use of the Debug Port in any fashion, I
do recommend grabbing a NET20DC, getting it to work somehow somewhere
maybe write some code for talking to it that is missing or buggy, and
documenting the process so others can make use of the device too.

If the goal is to educate yourself about USB and make a very narrow
hack then I say go for it, just be prepared for the effort. Except
time you'll either have to use an existing USB2 device controller
devkit, or design your own PCB and purchase lots of chips. Either
way, it is not so easy to reproduce your effort for another DIY:er.
Finally you could then fall back to the other purpose, to use your
DIY:ed device in order to help with debug target software for
communicating with a debugger host through the debug device, but by
then maybe someone has already used the NET20DC to do that.

So - comes down to why you want to do it. :)


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