I am using the RangeTest example code.
Playing around some more, I think the binary is being built wrong, so it does not actually run.
I probed around with an oscilloscope, and no (external) pins have any transitions, including all the Sx pins. So my guess is that the code is built, flashed into the Flutter, but then immediately crashes. Power cycle does not help.
The other clue to my guess is that whenever I change something (like board type, or the boards.txt file in the library) I get the following error in the IDE:
Build options changed, rebuilding all
arm-none-eabi-g++: error: core/syscalls_sam3.c.o: No such file or directory
exit status 1
Error compiling for board Flutter Basic.
retrying several times clears the error, and has a "successful" build, that can be flashed, but I wonder if it is actually working (or complete?) code.
googling that error has several suggestions of renaming options (related to other board types), none of which help.
I get this error both on Mac and Linux versions, so I suspect it has to do with the flutter library downloaded as part of the install process, probably due to different versions since it was built?
(I am using the current 1.8.5 IDE from www.arduino.cc)
According to another post here, the SerialUSB.print is no longer needed, but I don't know if that code was ever released?
In my case, the flutter is completely dead on reboot, so there is no serial activity, and the USB driver is not running, so the host laptop does not see any device at all.
Thanks for any help...