@PatkirkMartin In order to toggle power via PX4 you can do the following: Set GPIO_CTL_CH to the AUX channel you'd like to use for this feature, e.g., 3 for RC_MAP_AUX3. Set the corresponding RC_MAP_AUX# to the button/switch you want to use. e.g. 10 for channel 10 on your RC transmitter.

@PatkirkMartin No, as I said a UART mapped to the applications processor would also work. PX4 has a split architecture on VOXL2 with all flight critical operations happening on the DSP and support functions such as Mavlink, logging, and data manager are on the applications processor. But there is flexibility to move functions between them as needed. So, to match the ELRS receiver with the Mavlink module you could run it on the applications processor instead of the DSP. However, you would need an expansion board that exposes such a connector.