Hi @Sn0west / @marimach77,
it's quite easy once figured out...
The connection is described in @marimach77's link but you don't have to worry about the first part as you don't need to access the actual console port to get the shell.
Just remove your SD card from the flight controller, this stops it from sending heartbeat info via the USB port.
Then, connect via USB and use a console program as described on the linked page and open the serial port corresponding to the USB port with 57600 8N1.
Now, you should be seeing a
Here, you can first type (make sure to remove the props before doing that!!!)
pwm test -c 12 -p 1200
this would send a 1200us pulse on channels 1 and 2. Another example:
pwm test -c 1234 -p 200
would send a 200us (OneShot) pulse to all four channels.
The pulse is sent until you cancel via Ctrl+C.
By the way: using this test mode was the only way for me to calibrate my ESCs for standard operation - send a 1950 pulse to all channels, apply power, cancel the command --> the sound of success from the ESC - never works with QGC).
Hope this helps,
Edit: For those of you who read this post and want to use the same procedure - it seems that at least with some master build states, the pwm test command would conflict with the output of the mc_att_controller (effectively causing jumping PWM values). This can be avoided by setting "mc_att_control stop" prior to the above sequence.