h1. Grbl - An embedded g-code interpreter and motion-controller for the Arduino/AVR328 microcontroller
    
Grbl is a no-compromise, high performance, low cost alternative to parallel-port-based motion control for CNC milling. It will run on a vanilla Arduino (Duemillanove/Uno) as long as it sports an Atmega 328. 

The controller is written in highly optimized C utilizing every clever feature of the AVR-chips to achieve precise timing and asynchronous operation. It is able to maintain more than 30kHz of stable, jitter free control pulses.

It accepts standards-compliant G-code and has been tested with the output of several CAM tools with no problems. Arcs, circles and helical motion are fully supported, as well as, other basic functional g-code commands. Functions and variables are not currently supported, but may be included in future releases in a form of a pre-processor.

Grbl includes full acceleration management with look ahead. That means the controller will look up to 18 motions into the future and plan its velocities ahead to deliver smooth acceleration and jerk-free cornering.

*Changelog for v0.8 from v0.7:*
  - *BETA status: _Under development. Code state may significantly change with each push as new features are integrated._*
  - Major structural overhaul to allow for multi-tasking events and new feature sets
  - New run-time command control: Feed hold (pause), Cycle start (resume), Reset (abort), Status reporting
  - Controlled feed hold with deceleration to ensure no skipped steps and loss of location.
  - After feed hold, cycle accelerations are re-planned and may be resumed.
  - Advanced homing cycle with direction and speed configuration options. (Requires limit switches.)
  - Limit pins are held normal high with an internal pull-up resister. Wiring only requires a normally-open switch connected to ground. (For both ends of an axis, simply wire two in parallel into the same pin.)
  - Hard limits option and plays nice with homing cycle, so switches can be used for both homing and hard limits.
  - Re-factored g-code parser with robust error-checking.
  - 6 work coordinate systems (G54-G59), offsets(G92), and machine coordinate system support. Work systems are stored in EEPROM and persistent.
  - G10 L2 and L20 work coordinate settings support. L2 sets one or more axes values. L20 sets the current machine position to the specified work origin.
  - Program stop(M0,M1*,M2,M30) initial support. Optional stop to do.
  - Coolant control(M7*,M8,M9) support. (M7 is a compile-time option).
  - System reset re-initializes grbl without resetting the Arduino and retains machine/home position and work coordinates.
  - Restructured planner and stepper modules to become independent and ready for future features.
  - Settings re-factoring to allow configuration without compiling of most features. (Still in progress).
  - Misc bug fixes and removed deprecated acceleration enabled code.  
  - Planned features: Axis acceleration and max speed individual settings, full-featured status reporting, runtime settings such as toggling block delete.
  - Advanced compile-time options: Up to 6 work coordinate systems(G54-G59), XON/XOFF flow control (limited support), direction and step pulse time delay.
  

*Important note for Atmega 168 users:* Going forward, support for Atmega 168 will be dropped due to its limited memory and speed. However, legacy Grbl v0.51 "in the branch called 'v0_51' is still available for use.

_The project was initially inspired by the Arduino GCode Interpreter by Mike Ellery_