Cannot get remote GDB to work

[Andrea Venturoli]

Hello.

I'm trying to debug through a serial cable, as described in:
> https://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-online-gdb.html

I followed the instruction (I believe correctly), but when I issue 
"target remote /dev/cuau0", I get:

> Remote debugging using /dev/cuau0
> Ignoring packet error, continuing...
> warning: unrecognized item "timeout" in "qSupported" response
> Ignoring packet error, continuing...
> Remote replied unexpectedly to 'vMustReplyEmpty': timeout



I tried launching "cu -l /dev/cuau0" on both sides: I can correctly see 
what I type in the debugging terminal appear on the host's screen, but 
not vice versa.
This starts working again, when I remove flags 0x80 from 
hint.uart.0.flags and change it back to 0x10 (default).


Any hint?

  bye & Thanks
	av.

P.S. Both machines are physical (no virtualization here), both are 
12.1/amd64 and both serial ports are dumb old style serial ports.