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protocol.c - controls Grbl execution protocol and procedures
Part of Grbl v0.9
Copyright (c) 2012-2014 Sungeun K. Jeon
Grbl is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Grbl is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Grbl. If not, see <>.
This file is based on work from Grbl v0.8, distributed under the
terms of the MIT-license. See COPYING for more details.
Copyright (c) 2009-2011 Simen Svale Skogsrud
Copyright (c) 2011-2012 Sungeun K. Jeon
#include "system.h"
#include "serial.h"
#include "settings.h"
#include "protocol.h"
#include "gcode.h"
#include "planner.h"
#include "stepper.h"
#include "motion_control.h"
#include "report.h"
static char line[LINE_BUFFER_SIZE]; // Line to be executed. Zero-terminated.
// Directs and executes one line of formatted input from protocol_process. While mostly
// incoming streaming g-code blocks, this also directs and executes Grbl internal commands,
// such as settings, initiating the homing cycle, and toggling switch states.
static void protocol_execute_line(char *line)
protocol_execute_runtime(); // Runtime command check point.
if (sys.abort) { return; } // Bail to calling function upon system abort
if (line[0] == 0) {
// Empty or comment line. Send status message for syncing purposes.
} else if (line[0] == '$') {
// Grbl '$' system command
} else if (sys.state == STATE_ALARM) {
// Everything else is gcode. Block if in alarm mode.
} else {
// Parse and execute g-code block!
void protocol_main_loop()
// ------------------------------------------------------------
// Complete initialization procedures upon a power-up or reset.
// ------------------------------------------------------------
// Print welcome message
// Check for and report alarm state after a reset, error, or an initial power up.
if (sys.state == STATE_ALARM) {
} else {
// All systems go!
sys.state = STATE_IDLE; // Set system to ready. Clear all state flags.
system_execute_startup(line); // Execute startup script.
// ---------------------------------------------------------------------------------
// Primary loop! Upon a system abort, this exits back to main() to reset the system.
// ---------------------------------------------------------------------------------
uint8_t iscomment = false;
uint8_t char_counter = 0;
uint8_t c;
for (;;) {
// Process one line of incoming serial data, as the data becomes available. Performs an
// initial filtering by removing spaces and comments and capitalizing all letters.
// NOTE: While comment, spaces, and block delete(if supported) handling should technically
// be done in the g-code parser, doing it here helps compress the incoming data into Grbl's
// line buffer, which is limited in size. The g-code standard actually states a line can't
// exceed 256 characters, but the Arduino Uno does not have the memory space for this.
// With a better processor, it would be very easy to pull this initial parsing out as a
// seperate task to be shared by the g-code parser and Grbl's system commands.
while((c = serial_read()) != SERIAL_NO_DATA) {
if ((c == '\n') || (c == '\r')) { // End of line reached
line[char_counter] = 0; // Set string termination character.
protocol_execute_line(line); // Line is complete. Execute it!
iscomment = false;
char_counter = 0;
} else {
if (iscomment) {
// Throw away all comment characters
if (c == ')') {
// End of comment. Resume line.
iscomment = false;
} else {
if (c <= ' ') {
// Throw away whitepace and control characters
} else if (c == '/') {
// Block delete NOT SUPPORTED. Ignore character.
// NOTE: If supported, would simply need to check the system if block delete is enabled.
} else if (c == '(') {
// Enable comments flag and ignore all characters until ')' or EOL.
// NOTE: This doesn't follow the NIST definition exactly, but is good enough for now.
// In the future, we could simply remove the items within the comments, but retain the
// comment control characters, so that the g-code parser can error-check it.
iscomment = true;
// } else if (c == ';') {
// Comment character to EOL NOT SUPPORTED. LinuxCNC definition. Not NIST.
// TODO: Install '%' feature
// } else if (c == '%') {
// Program start-end percent sign NOT SUPPORTED.
// NOTE: This maybe installed to tell Grbl when a program is running vs manual input,
// where, during a program, the system auto-cycle start will continue to execute
// everything until the next '%' sign. This will help fix resuming issues with certain
// functions that empty the planner buffer to execute its task on-time.
} else if (char_counter >= (LINE_BUFFER_SIZE-1)) {
// Detect line buffer overflow. Report error and reset line buffer.
iscomment = false;
char_counter = 0;
} else if (c >= 'a' && c <= 'z') { // Upcase lowercase
line[char_counter++] = c-'a'+'A';
} else {
line[char_counter++] = c;
// If there are no more characters in the serial read buffer to be processed and executed,
// this indicates that g-code streaming has either filled the planner buffer or has
// completed. In either case, auto-cycle start, if enabled, any queued moves.
protocol_execute_runtime(); // Runtime command check point.
if (sys.abort) { return; } // Bail to main() program loop to reset system.
return; /* Never reached */
// Executes run-time commands, when required. This is called from various check points in the main
// program, primarily where there may be a while loop waiting for a buffer to clear space or any
// point where the execution time from the last check point may be more than a fraction of a second.
// This is a way to execute runtime commands asynchronously (aka multitasking) with grbl's g-code
// parsing and planning functions. This function also serves as an interface for the interrupts to
// set the system runtime flags, where only the main program handles them, removing the need to
// define more computationally-expensive volatile variables. This also provides a controlled way to
// execute certain tasks without having two or more instances of the same task, such as the planner
// recalculating the buffer upon a feedhold or override.
// NOTE: The sys.execute variable flags are set by any process, step or serial interrupts, pinouts,
// limit switches, or the main program.
void protocol_execute_runtime()
uint8_t rt_exec = sys.execute; // Copy to avoid calling volatile multiple times
if (rt_exec) { // Enter only if any bit flag is true
// System alarm. Everything has shutdown by something that has gone severely wrong. Report
// the source of the error to the user. If critical, Grbl disables by entering an infinite
// loop until system reset/abort.
if (rt_exec & (EXEC_ALARM | EXEC_CRIT_EVENT)) {
sys.state = STATE_ALARM; // Set system alarm state
// Critical events. Hard/soft limit events identified by both critical event and alarm exec
// flags. Probe fail is identified by the critical event exec flag only.
if (rt_exec & EXEC_CRIT_EVENT) {
if (rt_exec & EXEC_ALARM) { report_alarm_message(ALARM_LIMIT_ERROR); }
else { report_alarm_message(ALARM_PROBE_FAIL); }
bit_false_atomic(sys.execute,EXEC_RESET); // Disable any existing reset
do {
// Nothing. Block EVERYTHING until user issues reset or power cycles. Hard limits
// typically occur while unattended or not paying attention. Gives the user time
// to do what is needed before resetting, like killing the incoming stream. The
// same could be said about soft limits. While the position is not lost, the incoming
// stream could be still engaged and cause a serious crash if it continues afterwards.
} while (bit_isfalse(sys.execute,EXEC_RESET));
// Standard alarm event. Only abort during motion qualifies.
} else {
// Runtime abort command issued during a cycle, feed hold, or homing cycle. Message the
// user that position may have been lost and set alarm state to enable the alarm lockout
// to indicate the possible severity of the problem.
bit_false_atomic(sys.execute,(EXEC_ALARM | EXEC_CRIT_EVENT));
// Execute system abort.
if (rt_exec & EXEC_RESET) {
sys.abort = true; // Only place this is set true.
return; // Nothing else to do but exit.
// Execute and serial print status
if (rt_exec & EXEC_STATUS_REPORT) {
// Execute a feed hold with deceleration, only during cycle.
if (rt_exec & EXEC_FEED_HOLD) {
// !!! During a cycle, the segment buffer has just been reloaded and full. So the math involved
// with the feed hold should be fine for most, if not all, operational scenarios.
if (sys.state == STATE_CYCLE) {
sys.state = STATE_HOLD;
sys.auto_start = false; // Disable planner auto start upon feed hold.
// Execute a cycle start by starting the stepper interrupt begin executing the blocks in queue.
if (rt_exec & EXEC_CYCLE_START) {
if (sys.state == STATE_QUEUED) {
sys.state = STATE_CYCLE;
st_prep_buffer(); // Initialize step segment buffer before beginning cycle.
if (bit_istrue(settings.flags,BITFLAG_AUTO_START)) {
sys.auto_start = true; // Re-enable auto start after feed hold.
} else {
sys.auto_start = false; // Reset auto start per settings.
// Reinitializes the cycle plan and stepper system after a feed hold for a resume. Called by
// runtime command execution in the main program, ensuring that the planner re-plans safely.
// NOTE: Bresenham algorithm variables are still maintained through both the planner and stepper
// cycle reinitializations. The stepper path should continue exactly as if nothing has happened.
// NOTE: EXEC_CYCLE_STOP is set by the stepper subsystem when a cycle or feed hold completes.
if (rt_exec & EXEC_CYCLE_STOP) {
if ( plan_get_current_block() ) { sys.state = STATE_QUEUED; }
else { sys.state = STATE_IDLE; }
// Overrides flag byte (sys.override) and execution should be installed here, since they
// are runtime and require a direct and controlled interface to the main stepper program.
// Reload step segment buffer
if (sys.state & (STATE_CYCLE | STATE_HOLD | STATE_HOMING)) { st_prep_buffer(); }
// Block until all buffered steps are executed or in a cycle state. Works with feed hold
// during a synchronize call, if it should happen. Also, waits for clean cycle end.
void protocol_buffer_synchronize()
// If system is queued, ensure cycle resumes if the auto start flag is present.
// Check and set auto start to resume cycle after synchronize and caller completes.
if (sys.state == STATE_CYCLE) { sys.auto_start = true; }
while (plan_get_current_block() || (sys.state == STATE_CYCLE)) {
protocol_execute_runtime(); // Check and execute run-time commands
if (sys.abort) { return; } // Check for system abort
// Auto-cycle start has two purposes: 1. Resumes a plan_synchronize() call from a function that
// requires the planner buffer to empty (spindle enable, dwell, etc.) 2. As a user setting that
// automatically begins the cycle when a user enters a valid motion command manually. This is
// intended as a beginners feature to help new users to understand g-code. It can be disabled
// as a beginner tool, but (1.) still operates. If disabled, the operation of cycle start is
// manually issuing a cycle start command whenever the user is ready and there is a valid motion
// command in the planner queue.
// NOTE: This function is called from the main loop and mc_line() only and executes when one of
// two conditions exist respectively: There are no more blocks sent (i.e. streaming is finished,
// single commands), or the planner buffer is full and ready to go.
void protocol_auto_cycle_start() { if (sys.auto_start) { bit_true_atomic(sys.execute, EXEC_CYCLE_START); } }
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