[coreboot] USB debug cables and emulation

[Peter Stuge]

On Fri, Jun 27, 2008 at 01:15:32PM -0400, Joseph Smith wrote:
> > 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?

Yes, but you have to register on their web site.


> >> 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:-)

Even if you have to buy 1000 pcs?


> > 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??

I expect it to be stored in internal memory in the microcontroller
package. I'll open my device up if I can find it to check if I
remember correctly about the Ubicom.


> > 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 :-)

USB has strict distinction between hosts and devices. This is a
fundamental design decision detailed pretty well in the spec.

In order to create your own Debug Class device you need to learn a
lot about devices and almost nothing about hosts.

When writing a USB stack for the host one needs to learn everything
about the Host Controller and almost nothing about devices.


> 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?

Yes.


> If so, how does it work?

USB serial port. CONFIG_USB_SERIAL_DEBUG enables the driver.


//Peter