teensy_debugdev: Can we make this USB EHCI debug jig work?

[Keith Hui]

Hi guys,

Now is the time to get some coreboot work done.

I found out about this code during a search:

https://github.com/avivgr/teensy_debugdev

It is to be programmed into an ATMega32u4 device that turns it into a
USB debug dongle and picks up serial chatter to be sent out via the
serial pins that can then be picked up by a TTL serial device of your
choice. Based on the USB VID:PID it is emulating a Net20DC. It goes
fine on to an Arduino Micro (that I just bought today for this
purpose) using another Arduino as the programmer. When I plug it into
my laptop It detects as a debug cable as expected, but when I plug it
into my p8z77-m with coreboot it isn't aware that I plugged it in when
I did, into any port. My coreboot build already has USB EHCI debug
dongle enabled and output turned on. Needless to say I got nothing
over this channel.

Did I miss something? How can we make this work?

Thanks
Keith

[Felix Held]

Hi Keith!
> Did I miss something? How can we make this work?

It won't work, since the ATMega32u4 only supports 1.5 and 12 MBit/s USB, 
but an EHCI debug dongle needs to support 480 MBit/s mode or it won't 
work. That's also why the ft(2)232h works as a slightly out-of-spec EHCI 
debug device (coreboot has some code to deal with it being slightly out 
of spec for an EHCI debug device), but the non h versions don't.

Regards
Felix