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


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?

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...