Normally one quits picocom with Ctrl-a Ctrl-x sequence of keys. However now I have a picocom-via-picocom situation where I'm running a picocom on a target which itself is accessed through a serial interface using picocom. Running the usual sequence only quits the topmost-level picocom.
I know escaping the Ctrl-a itself is possible, so that it can be sent to the lower-level picocom, thus letting it be controlled. I used to do that regularly but have since forgotten how that's done and can't find the information anywhere. Can someone refresh my memory?