This is a discussion for the 1MB flash limit issue so that we can consolidate any discussions and concerns about it in one place.
To give some background, all Pixhawk (and compatible) boards use STMicroelectronics's STM32F427 as their main CPU. This CPU is advertised as having 2MB of flash space (flash is where the ardupilot software is held) but we have discovered that early revisions of this CPU (RevA, RevY and Rev1) have a hardware problem and can actually only hold 1MB and if we use more than that they start exhibiting USB communication problems.
Now currently APM:Copter-3.4 is 0.9MB so it's under the limit but as we add new features it grows and if it grows above 1MB users will find they can't reliable connect the ground station to the board using a USB cable (wireless would still work) which could make it very difficult to configure the board, download logs, etc.
We think many boards (perhaps most boards) out there are the early revisions (A, Y or 1) which suffer from this problem. All the boards on my desk have this problem and you can check your board by following the instruction also shown in the video:
Some very recent boards do not suffer from this problem. For example all Solo's are fine as are the XRacer (aka PixRacer) boards.
Before panic ensues I'd like to say that although APM:Copter-3.3.2 is already 90% of this limit, remember we've just done a release and we will put effort into keeping the code size under 1MB. So for example, I can guarantee that APM:Copter-3.4 will fit and hopefully Copter-3.5 too.
Still, when you're shopping for your next Pixhawk you may consider asking the manufacturer if they are using the latest Rev3 STM32F427 processor.
Damn. This would have been nice to know back in July 2014 when I bought it! Oh well...