GRBL CoreXY -- Newmatik Fork

A fork of gnea/grbl (v1.1) pre-configured for CoreXY kinematics and a macOS command-line build chain. Targets the Arduino Uno R3 (ATmega328P).

What Changed from Upstream

Change	File
CoreXY kinematics enabled	grbl/config.h -- #define COREXY
Homing cycles reconfigured for CoreXY (X and Y homed separately)	grbl/config.h -- HOMING_CYCLE_0/1/2
Programmer set to Arduino USB bootloader	Makefile -- PROGRAMMER
Removed old commit logs and Arduino IDE example sketches	doc/log/, grbl/examples/

Prerequisites (macOS)

1. Homebrew

If you don't have Homebrew yet:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

2. AVR Toolchain

GRBL requires avr-gcc 7.x to fit within the ATmega328P's 32 KB flash. Newer versions (9.x+) produce significantly larger binaries that exceed the flash limit.

Recommended: Install the Arduino IDE (even if you won't use it directly). It ships avr-gcc 7.3.0 which the Makefile auto-detects:

• Download from arduino.cc
• Open it once and install the Arduino AVR Boards package via Tools > Board > Boards Manager
• The toolchain will be installed to ~/Library/Arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/

You also need avrdude for flashing (the Arduino IDE bundles one, but the Makefile uses the system avrdude):

brew install avrdude

Verify the installation:

~/Library/Arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc --version
avrdude -v

Alternative: If you want to use Homebrew's avr-gcc, install version 8:

brew tap osx-cross/avr
brew install avr-gcc@8

Then point the Makefile to it:

make AVR_TOOLCHAIN="$(brew --prefix avr-gcc@8)/bin"

3. VS Code / Cursor Extension (optional)

Install the C/C++ extension (ms-vscode.cpptools) for IntelliSense and code navigation.

Build

Compile the firmware from the project root:

make clean && make

The Makefile auto-detects the Arduino IDE's avr-gcc 7.3.0 on macOS. To use a different toolchain, override the path:

make AVR_TOOLCHAIN=/path/to/avr-gcc/bin

This produces grbl.hex in the project root directory. The build output shows the firmware size -- it must be under 32,768 bytes (32 KB) to fit in the ATmega328P flash.

Flash to Arduino Uno

1. Find Your Serial Port

Plug in the Arduino Uno via USB and identify the serial device:

ls /dev/cu.usbmodem*

You should see something like /dev/cu.usbmodem11401.

2. Flash

If the Makefile's PROGRAMMER line already matches your serial port (it uses a wildcard by default), simply run:

make flash

If you have multiple serial devices, specify the exact port:

make flash PROGRAMMER="-c arduino -P /dev/cu.usbmodem11401 -b 115200"

3. Verify

Connect to the Arduino with a serial terminal at 115200 baud to confirm GRBL is running:

screen /dev/cu.usbmodem11401 115200

You should see a GRBL welcome message. Press Ctrl-A then K then Y to exit screen.

Configuration

All compile-time configuration lives in two files:

• grbl/config.h -- Feature toggles (CoreXY, homing, safety door, laser mode, etc.)
• grbl/defaults.h -- Default machine parameters (steps/mm, max rates, acceleration, travel limits)

After editing either file, rebuild and re-flash:

make clean && make && make flash

Runtime settings (steps/mm, acceleration, etc.) can also be changed over serial with $ commands without recompiling. See doc/markdown/settings.md for the full settings reference.

CoreXY Notes

• CoreXY is enabled via #define COREXY in grbl/config.h.
• The A and B motors must have the same steps/mm. Set $100 and $101 to identical values.
• Homing is configured to home Z first, then X, then Y in separate cycles (required for CoreXY).
• If motions move in unexpected directions, check motor wiring against the CoreXY theory.

Project Structure

.
├── Makefile              # Build and flash configuration
├── COPYING               # GPLv3 license
├── grbl/                 # Firmware source code
│   ├── config.h          # Compile-time feature configuration
│   ├── defaults.h        # Default machine parameters
│   ├── cpu_map.h         # ATmega328P pin mapping
│   ├── main.c            # Entry point
│   ├── stepper.c/h       # Stepper motor driver
│   ├── planner.c/h       # Motion planner with look-ahead
│   ├── gcode.c/h         # G-code parser
│   ├── motion_control.c/h
│   ├── serial.c/h        # UART communication
│   └── ...               # Additional modules
├── build/                # Compiled object files (gitignored)
└── doc/
    ├── csv/              # Error, alarm, and setting code references
    ├── markdown/         # Commands, settings, jogging, laser mode docs
    └── script/           # Python streaming scripts for testing

Supported G-Codes

Non-Modal Commands: G4, G10L2, G10L20, G28, G30, G28.1, G30.1, G53, G92, G92.1
Motion Modes:       G0, G1, G2, G3, G38.2, G38.3, G38.4, G38.5, G80
Feed Rate Modes:    G93, G94
Unit Modes:         G20, G21
Distance Modes:     G90, G91
Arc IJK Distance:   G91.1
Plane Select:       G17, G18, G19
Tool Length Offset: G43.1, G49
Cutter Comp:        G40
Coord Systems:      G54, G55, G56, G57, G58, G59
Control Modes:      G61
Program Flow:       M0, M1, M2, M30
Coolant Control:    M7*, M8, M9
Spindle Control:    M3, M4, M5
Valid Words:        F, I, J, K, L, N, P, R, S, T, X, Y, Z

Credits

This is a fork of GRBL by Sungeun "Sonny" Jeon (@chamnit), built on the original Grbl v0.6 by Simen Svale Skogsrud.

License

GPLv3. See COPYING for the full license text.