Compilation Problem

This is my first attempt at building the APM code. I have cloned all the relevant firmware (ArduPlane V3.3.1beta1) and done a successful build, and then used Mission Planner to program my Pixhawk. All appeared to go as planned, and the Mission Planner reports the correct software version. So, next job is to make a minor modification to the code, and prove that I can build/program this to the Pixhawk. For my first attempt I just changed the #define THISFIRMWARE, in Plane.h, to something different and rebuilt the code. When I tried to reprogram the Pixhawk, I got a message telling me “no need to upload, already on the unit”. For my next attempt, I tried making a minor change to ArduPlane.cpp, but still I get the same message. I’ve looked through all of the posts on here relating to code building, and also the info on ardupilot.com, but haven’t found anything that might help.

Digging through the code, I think my problem may be due to using “make”, and somehow this is forcing the FIRMWARE_STRING to be the same as GIT_VERSION. I am assuming that Mission Planner compares the firmware string from the unit to the string of the code that is to be programmed? If this is the case, how do I do a build whereby FIRMWARE_STRING becomes assigned with my value that I have defined in THISFIRMWARE?

Can someone please offer me some help with this. I can’t load any new code until I can get this sorted!