This took me some time to find out, and it could be useful (A06):
If you install the xserver-xorg-input-joystick package (and restart X11 or reboot), the DevTerm’s joystick (the directional keys in the upper left & right corners) will emulate a mouse. Moving the mouse with the joystick directional keys is great, you can swing from left to right in an instant; less so for precise movement, but that’s what the trackball is for. The ABXY keys simulate different mouse buttons, which is less useful. But you can remap the actions to something else.
So far so good, but if you launch an application that has native support for a joystick, then you will get mouse movements and clicks in addition to the joystick events - not optimal.
To fix the issue, install xinput and then the command xinput set-prop pointer:'ClockworkPI DevTerm' 'Generate Mouse Events' 0 stops the mouse emulation, while your joystick still works. Replace 0 with 1 to re-enable the emulation (i.e. create a wrapper around the application that needs the joystick to disable and then enable mouse emulation).
- both have additional issues I am now fighting with though, but unrelated to the joystick.