GRBL Study

GRBL Introduction to

Grbl Is used for CNC The motion control of milling based on parallel port is absolutely , High performance , Low cost alternatives . Just run Atmega 328, It will be Arduino（Duemillanove / Uno） Up operation .

The controller is highly optimized C Language writing , utilize AVR All the ingenious functions of the chip to realize accurate timing and asynchronous operation . It can last up to 30kHz The stability of the , Jitter free control pulse .

It accepts... That meets the standards g Code , And has passed a variety of CAM The output of the tool is tested , No problem . Fully support arc , Circular and helical motion , And all other major g Code command . Macro functions are not supported , Variables and most fixed loops , But we think that GUI They can be better converted into direct g Code .

GRBL Of GitHub Warehouse

https://github.com/grbl/grbl

Start with the file directory

Just from GitHub Downloaded grbl after , It can be used directly vscode Open the whole folder , remove git Some documents and readme outside , In fact, only 3 A folder ：

• build
• doc
• grbl
  In fact, it seems to know ,build and doc It has nothing to do with the source code , They will only include some files stored after compilation or some description documents, or some dependent scripts that need to be downloaded during compilation . about Arduino Come on , Not all source files or dependent files will appear in the project , More time , After selecting some chips , By writing in advance py Script , Automatically link and download the corresponding chip dependency file , So as to reduce the capacity of the whole project .

Get into GRBL

cpu_map

The focus of the whole warehouse is grbl This folder .

As you can see from the diagram ,grbl In the folder of , contain ：

• cpu_map
• defaults
• examples
• Related driver files
  from cpu_map You can see , It contains two header files , namely ：
  
  That's what I've just introduced GRBL Described when , Support 328P and 2560 Two AVR chip . These two are also Arduino The classic of development board （ It is estimated that foreigners like Arduino, After all, it's easy to use ）.
  If you want to transplant, of course, you must know what's inside , After opening it, it's like this ：
  
  Analyze it bit by bit ：

#define GRBL_PLATFORM "Atmega328p"

Here is used to define the name of the chip , It's easy to understand .

// Define serial port pins and interrupt vectors.
#define SERIAL_RX USART_RX_vect
#define SERIAL_UDRE USART_UDRE_vect

This place , It is used to define the pin and interrupt vector of the serial port .

// Define step pulse output pins. NOTE: All step bit pins must be on the same port.
#define STEP_DDR DDRD
#define STEP_PORT PORTD
#define X_STEP_BIT 2 // Uno Digital Pin 2
#define Y_STEP_BIT 3 // Uno Digital Pin 3
#define Z_STEP_BIT 4 // Uno Digital Pin 4
#define STEP_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits

// Define step direction output pins. NOTE: All direction pins must be on the same port.
#define DIRECTION_DDR DDRD
#define DIRECTION_PORT PORTD
#define X_DIRECTION_BIT 5 // Uno Digital Pin 5
#define Y_DIRECTION_BIT 6 // Uno Digital Pin 6
#define Z_DIRECTION_BIT 7 // Uno Digital Pin 7
#define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits

// Define stepper driver enable/disable output pin.
#define STEPPERS_DISABLE_DDR DDRB
#define STEPPERS_DISABLE_PORT PORTB
#define STEPPERS_DISABLE_BIT 0 // Uno Digital Pin 8
#define STEPPERS_DISABLE_MASK (1<<STEPPERS_DISABLE_BIT)

// Define homing/hard limit switch input pins and limit interrupt vectors. 
// NOTE: All limit bit pins must be on the same port, but not on a port with other input pins (CONTROL).
#define LIMIT_DDR DDRB
#define LIMIT_PIN PINB
#define LIMIT_PORT PORTB
#define X_LIMIT_BIT 1 // Uno Digital Pin 9
#define Y_LIMIT_BIT 2 // Uno Digital Pin 10
#ifdef VARIABLE_SPINDLE // Z Limit pin and spindle enabled swapped to access hardware PWM on Pin 11. 
  #define Z_LIMIT_BIT 4 // Uno Digital Pin 12
#else
  #define Z_LIMIT_BIT 3 // Uno Digital Pin 11
#endif
#define LIMIT_MASK ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits
#define LIMIT_INT PCIE0 // Pin change interrupt enable pin
#define LIMIT_INT_vect PCINT0_vect 
#define LIMIT_PCMSK PCMSK0 // Pin change interrupt register

Is this paragraph very long ？ But take a closer look , Nothing ,GRBL In fact, printing is realized by controlling the motor , Similar to 3D Printer i3 Structure . So we need to define ：

• X/Y/Z Direction control pin , This pin is used to control the operation direction of the motor .
• Stepper motor enable pin , That is to control whether the stepping motor can move through this pin .
• Limit switch detection pin , That is, the motor is moving to 0 A.m. , After triggering the limit switch , Need to stop right now , Otherwise, it is easy to damage the machine structure .
  Analyze it like this , It's easy .

// Define probe switch input pin.
#define PROBE_DDR DDRC
#define PROBE_PIN PINC
#define PROBE_PORT PORTC
#define PROBE_BIT 5 // Uno Analog Pin 5
#define PROBE_MASK (1<<PROBE_BIT)

// Start of PWM & Stepper Enabled Spindle
#ifdef VARIABLE_SPINDLE
  // Advanced Configuration Below You should not need to touch these variables
  #define PWM_MAX_VALUE 255.0
  #define TCCRA_REGISTER TCCR2A
  #define TCCRB_REGISTER TCCR2B
  #define OCR_REGISTER OCR2A
  
  #define COMB_BIT COM2A1
  #define WAVE0_REGISTER WGM20
  #define WAVE1_REGISTER WGM21
  #define WAVE2_REGISTER WGM22
  #define WAVE3_REGISTER WGM23
      
  // NOTE: On the 328p, these must be the same as the SPINDLE_ENABLE settings.
  #define SPINDLE_PWM_DDR DDRB
  #define SPINDLE_PWM_PORT PORTB
  #define SPINDLE_PWM_BIT 3 // Uno Digital Pin 11

about GRBL for , Use CNC Words , With the function of laser head , The laser head uses PWM Control mode control , Of course, it also has a probe .

There are so many general analysis , In fact, you can go and see 2560 The header file , You'll find it's basically the same . Therefore, these two header files directly indicate , Use it normally GRBL Words ,MCU What function pins need to be provided . So we can also start the first step of transplantation ------ Pin assignments .

defaults

After entering , See several defaults Header file starting with name , Careful can be found on the name , This should be an adaptive configuration according to different models .

You can open any file to see ：

you 're right , The file is extremely simple , It's just a configuration file ！ Used to configure CNC Related parameters of , For example, the number of pulses of the motor and so on . Specific configuration , When transplanting later, if you encounter , Let's go into more detail .

examples

This folder is useless , It's in there Arduino Engineering documents of . because GRBL Is based on Arduino It's done , So the compiler will use Arduino To compile .

The rest of the transplants are analyzed one by one .

Transplant preparation

For this GRBL Transplantation , I intend to transplant it to two chips ：

• STM32F446RC
• i.MX RT1010 EVK （ I applied to ！ Happy ！）
  One is M4 One of the kernel is M7 The kernel of , because GRBL The motion has a computational complement algorithm , Choosing a chip with floating-point operation will feel very good .

… Development board design …ing！