I am looking through the Ardupilot source code for some specifics on how it records data for the Pixhawk. The program uses the PX4 firmware to interact with the Pixhawk, so I suspect it uses the built in sdlog2 functionality.
However Ardupilot uses a Dataflash system for its logging.
Which of these functions is used for logging data in this case?
You need to ask that over at discuss.ardupilot.org