#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 m aintain 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 v0.9 from v0.8

• ALPHA status: Under heavy development.
• New stepper algorithm: Based on the Pramod Ranade inverse time algorithm, but modified to ensure steps are executed exactly. This algorithm performs a constant timer tick and has a hard limit of 30kHz maximum step frequency. It is also highly tuneable and should be very easy to port to other microcontroller architectures. Overall, a much better, smoother stepper algorithm with the capability of very high speeds.
• Planner optimizations: Multiple changes to increase planner execution speed and removed redundant variables.
• Acceleration independence: Each axes may be defined with different acceleration parameters and Grbl will automagically calculate the maximum acceleration through a path depending on the direction traveled. This is very useful for machine that have very different axes properties, like the ShapeOko z-axis.
• Maximum velocity independence: As with acceleration, the maximum velocity of individual axes may be defined. All seek/rapids motions will move at these maximum rates, but never exceed any one axes. So, when two or more axes move, the limiting axis will move at its maximum rate, while the other axes are scaled down.
• Significantly improved arc performance: Arcs are now defined in terms of chordal tolerance, rather than segment length. Chordal tolerance will automatically scale all arc line segments depending on arc radius, such that the error does not exceed the tolerance value (default: 0.005 mm.) So, for larger radii arcs, Grbl can move faster through them, because the segments are always longer and the planner has more distance to plan with.
• Soft limits: Checks if any motion command exceeds workspace limits. Alarms out when found. Another safety feature, but, unlike hard limits, position does not get lost, as it forces a feed hold before erroring out.
• New Grbl SIMULATOR by @jgeisler: A completely independent wrapper of the Grbl main source code that may be compiled as an executable on a computer. No Arduino required. Simply simulates the responses of Grbl as if it was on an Arduino. May be used for many things: checking out how Grbl works, pre-process moves for GUI graphics, debugging of new features, etc. Much left to do, but potentially very powerful, as the dummy AVR variables can be written to output anything you need.
• Homing routine updated: Sets workspace volume in all negative space regardless of limit switch position. Common on pro CNCs. Also reduces soft limits CPU overhead.
• Feedrate overrides: In the works, but planner has begun to be re-factored for this feature.
• Jogging controls: Methodology needs to be to figured out first. Could be dropped due to flash space concerns. Last item on the agenda.

The project was initially inspired by the Arduino GCode Interpreter by Mike Ellery