According to 3DR, it's a "customized OpenTx" firmware, but they can't provide me a link to a repository, and they can't confirm what changes have been made to it (they told me some stuff that doesn't sound right to me). I would like to update to a newer version of OpenTx, but without knowing what mods they made I'm scared (maybe something important won't work without the changes, or worse I'll have a fly-away). I can save and reload the firmware with Companion9x, but I'm unable to modify anything in the gui and save the changes to the tx, it results in an invalid EEPROM and reformat on the transmitter (so I think whatever they did makes it not entirely compatible with Companion9x).
Does anyone have any info on what the heck 3DR put on this transmitter, preferably location of the source code? If not and 3DR is modifying the opensource OpenTx, shouldn't they provide source code? I'm pretty new to the RC world, so it's possible I'm just missing something, but this seems odd to me.
FYI, 3D Robotics response to my inqueries about firmware, and what is custom about the firmware (does anyone else think this couldn't be the right answer?):
We don't have that information [on what firmware it's using] we're truly sorry. The changes that were made were so that the sticks are in mode 2 and the controller knows it will operate a copter, not a plane. Also, the parameters are specified to handle a certain weight.