@kcmacauley , the voxl-esc driver is implemented in PX4, so you can see how the data packets are generated to send RPM commands and receive the feedback from each ESC.
https://github.com/modalai/px4-firmware/blob/voxl-dev/src/drivers/actuators/voxl_esc/voxl_esc.cpp#L1230
https://github.com/modalai/px4-firmware/blob/voxl-dev/src/drivers/actuators/voxl_esc/voxl_esc.cpp#L1252
Also, an outdated implementation, which you can also refer to, can be found here : https://gitlab.com/voxl-public/support/esc-driver -- it can be compiled and tested standalone, but we do not maintain or support it.
Our voxl-esc python tools provide a lot more functionality, but not entirely open source : https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc
Finally, an even more outdated (but more formal) document can be found here : https://developer.qualcomm.com/qfile/34042/80-p4698-19_b_qualcomm_snapdragon_navigator_esc_protocol_spec.pdf. Also, not supported or complete, but can be used as a reference.
If you have any specific questions about protocol, I can answer, but you should be able to get what you need for basic flight from the PX4 driver. For offline testing and tuning it is best to use the voxl-esc python tools.
Alex