[coreboot] USB debug cables and emulation

Peter Stuge peter at stuge.se
Fri Jun 27 23:38:11 CEST 2008

On Fri, Jun 27, 2008 at 03:34:20PM -0400, Joseph Smith wrote:
> >> > I'll open my device up if I can find it to check if I remember
> >> > correctly about the Ubicom.
> >>
> >> Thanks that would help a lot.
> > 
> > To be honest, I don't think it would help at all, but I appreciate
> > the curiosity and will be glad to provide photos when I find my
> > device! :)
> Photos, will help it will show me if there are little caps,
> resisters, diodes, etc between chips.

Sure, there will be some passives to glue the three major blocks

> >> > USB serial port. CONFIG_USB_SERIAL_DEBUG enables the driver.
> >>
> >> So if this is enabled in in the kernel, what kind of device does
> >> it show up as in the serial terminal emulator?
> > 
> > I don't understand. A serial terminal emulator doesn't really
> > know about devices.
> Yes it does, the emulator needs to know what port/device to connect
> to (ex. /dev/ttyS0, /dev/ttyS1, /dev/ttyUSB0, etc)

Oh that kind of device! :)

> > You get one /dev/ttyUSBx serial port. Bytes sent out on the EHCI
> > Debug Port on the system being debugged will be coming in on that
> > serial port on the debugger host, and vice versa.
> Ok, that makes sense, I have a USB-> Serial adapter for my laptop
> that comes up as /dev/ttyUSB0. So Linux signifys the USB debugger
> as a USB serial device(/dev/ttyUSBx). If so that answers that
> question.


Note that the NET20DC isn't any kind of debugger, it can be thought
of as a special type of proxy for USB transfers.

On Fri, Jun 27, 2008 at 09:43:50PM +0200, Carl-Daniel Hailfinger wrote:
> I think the design might become easier if you just create the debug
> part of the device and use the serial side of a plain usbserial
> device as direct interface.

Actually I suggested something along those lines already in the wiki
page. :)

But if someone is learning enough to make their own debug class
device, it will be mostly a copypaste exercise to include a USB
interface also for the other end.

> And Peter will hate the statement above.

:) Mh, not so bad.

Looking at the economics of this project again, it requires the price
to go down another $20, to make room for a USB-serial converter.
(Though that has more uses, so maybe one could reduce that figure.)


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