[coreboot] USB Debug support

Peter Stuge peter at stuge.se
Wed Jul 2 14:27:48 CEST 2008


On Wed, Jul 02, 2008 at 07:45:25AM -0400, Gregg C Levine wrote:
> A USB cable configured to connect two systems together, such as a
> laptop to receive files from a desktop is simply two USB-A cables
> wired to an appropriate logic array. This would (Or "should be".
> Either way) probably be the latest generation in USB Gadget
> hardware.

Yes. But the logic "array" is quite complex, and implements several
layers of protocol. Please look at chapters 5, 8 and 9 in the USB
specification for a description of the protocol.

> Ideally a Linux system can use this to talk to an appropriately
> configured system, provided the target was built using the debug
> features turned on for the USB stack layer.

Not enough. These are the hardware requirements:

* The target USB controller must be EHCI
* The target USB controller must implement the optional Debug Port
* The target board must have a USB connector for the physical port
  that supports Debug Port. It is always only one particular port.
* The "cable" must implement the Debug Device functional
  specification. See links on http://coreboot.org/EHCI_Debug_Port

> While I have here hardware for trying out this idea, namely my
> Linux development station, I have not as yet chosen a target.

You will also need the debug device. I suggest ordering the NET20DC
product from semiconductorstore.com.


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