The document InvenSense CA-SDK 5.1.1 states that "The option to load the program through BSL requires the existing software on the CA-SDK Board to have a BSL jump with a user interface. The software that is pre flashed on all CA-SDK boards that are shipped does come with the option of pressing the button to put the CA-SDK in BSL where the user can update their software using USB interface. A similar interface is recommended for any software updates from the developer to make this feature available. For the software shipped with CA-SDK, holding the button for two seconds with USB connected allows for BSL jump."
My question is the following: which button on the board needs to be pressed in order to load software via the bootloader? I am confused because 2 existing buttons exist on the MPU 9250 CA-SDK board, SW1 and SW2, but the documentation does not state which button should be used to enable this functionality.