Enabling AUX output channels on Pixhawk

We are writing our own application (via Pixhawk PSP).
We can’t seem to enable the AUX outputs. We don’t have a /dev/pwm_output1 device.
(we have all 8 main PWM outputs used already)

Is there any magic in getting the AUX outputs enabled? Any documentation on how actuator_controls, actuator_armed and actuator_outputs topics work together?

Can someone provide code that will do this?

Seems that I have to use nsh> fmu mode_pwm4 first to enable this mode
What is the difference between model_pwm and mode_pwm4?

OK. I see the mode_pwm is full control and mode_pwm4 is for the first 4 (5 & 6 are GPIO then).

I got this working by opening the /dev/pwm_output1 device which appeared once I set fmu mode_pwm.