PX4 Firmware selection


I can’t create my own topic in the forum therefore I post a “reply” to ask a question:

I have managed to build the ArduPilot for Copter firmware under Windows, in the ArduCopter.pde, the version indicates APM:Copter V3.3-dev. My hardware is PixHawk. I like to know which firmware should I download to the PixHawk?
Under …/PX4Firmware/build, there are px4fmu-v1_APM.build, px4fmu-v2_APM.build, px4io-v1_default.build and px4io-v2_default.build I but guess it should be firmware.px4, right?
Under …/ArduCopter, there are ArduCopter-v1.px4 and ArduCopter-v2.px4, what are these two files for?

Please help to clarify.