Now the end year holidays are passed it is time to continue with my g2core shield.
My shield is based on the Arduino DUE pinout in https://github.com/synthetos/g2/wiki/Arduino-DUE-Pinout-for-g2core. I have checked out the g2core source code and managed to compile it with Linux. I compiled it with BOARD=gShield as my guess whas that being the closest matching BOARD, but it turned out (in gShield-pinout.h) that the spindle direction pin is set to -1 (not used?) and it is indeed not set on the Due. By modifying it locally to use pin13, spindle direction does work properly.
After reading the development pages on the g2core wiki it is yet not clear to me why the spindle direction pin is not used by default on the gShield. Can someone from @Synthetos give some direction why that is the case?
Of course I can try to add a new pinout definition for my own g2core shield, but it would be better if the gShield BOARD can be re-used.