How to get into ddb on RPi3 (cdce0 related hang debugging)

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How to get into ddb on RPi3 (cdce0 related hang debugging)

Karel Gardas

Hi,

I'm playing with 6.3-current on RPi3. I'm trying to
hang into it another NIC, so far using recommended (by rpi community)
hardware (TP-Link UE300, Lenovo Thinkpad USB GigEthernet adapter) but
I'm out of luck on OpenBSD. Once I start dhcp on cdce0 using:

sh /etc/netstart cdce0

where /etc/hostname.cdce0 contains just "dhcp", the system kind of
freeze. I'm not able to Ctrl-C from running netstart back to shell.
I've enabled ddb by putting ddb.console=1 into my /etc/sysctl.conf, but
I'm not able to get into it once freeze happen using pressing ~# on my
serial console. In fact I'm not able to get into ddb even when system
is normaly running so I guess my sequence of action to get into it is
kind of wrong.

Of course, I'll switch debugging in cdce and see what it reveals, but I
guess I'll need to add few printfs here and there and for this knowing
the place of hang may help.

Any idea how to drop into ddb on RPi3?

Thanks!
Karel
PS: the hardware is capable well of driving another usb->ethernet, I've
verified on debian unstable, raspbian and even on netbsd, so hardware
should be kind of ok. Hence attempt on OBSD debugging...