New features in the current CNCL release require GRBL changes. These changes are implemented in this GRBL fork. The Compiler Options are described in the GRBL-L-Mega Wiki. For all other information read the GRBL Mega Wiki
I have added spindle sync threading G33 based on fschill grbl version to this GRBL-L-Mega version and the version for the Arduino Uno GRBL-L. Read the threading setup Wiki for an explanation of the threading setup.

Ramps 1.4 - 1.6 users, use the Ramps branch.