Merge pull request #21 from bkp23/master

Thanks for the helpful code comments!

grbl-lpc/delay.cpp

@@ -22,11 +22,11 @@
 
 void delay_init()
 {
-    LPC_TIM3->CTCR = 0;   // timer mode
+    LPC_TIM3->CTCR = 0;   // Count Control (0=TimerMode, 1-3=EdgeCounterMode)
-    LPC_TIM3->PR = 0;     // no prescale
+    LPC_TIM3->PR = 0;     // no Prescale (TC increments ever PR+1 clocks)
-    LPC_TIM3->MCR = 0;    // no MR actions
+    LPC_TIM3->MCR = 0;    // no Match Control actions
-    LPC_TIM3->CCR = 0;    // no capture
+    LPC_TIM3->CCR = 0;    // no Capture Control actions
-    LPC_TIM3->EMR = 0;    // no external match
+    LPC_TIM3->EMR = 0;    // no External Match (controls external match pins)
-    LPC_TIM3->TCR = 0b10; // reset
+    LPC_TIM3->TCR = 0b10; // reset Timer Control (0b10=Reset, 0b01=Enable)
-    LPC_TIM3->TCR = 0b01; // enable
+    LPC_TIM3->TCR = 0b01; // enable Timer Control (0b10=Reset, 0b01=Enable)
 }

grbl-lpc/flash.cpp

@@ -25,37 +25,38 @@ static constexpr unsigned flash_addr = 0xF000;                    // Last 4k sec
 static constexpr unsigned flash_size = 1024;                      // Only using 1k of a 4k sector
 static char *flash_memory = (char *)flash_addr;                   // Flash memory
 static char flash_buffer[flash_size] __attribute__((aligned(4))); // Copy of flash memory
-using Iap = void(unsigned[], unsigned[]);                         // IAP entry point
+using Iap = void(unsigned[], unsigned[]);                         // IAP entry point function
-static const Iap *iap = (Iap *)0x1FFF1FF1;                        // IAP entry point
+static const Iap *iap = (Iap *)0x1FFF1FF1;                        // IAP entry point address
 
 void eeprom_init()
 {
-    memcpy(flash_buffer, flash_memory, flash_size);
+    memcpy(flash_buffer, flash_memory, flash_size);  // Copy flash memory into local flash buffer
 }
 
 void eeprom_commit()
 {
     if (!memcmp(flash_buffer, flash_memory, flash_size))
-        return;
+        return; // No changes to commit
     unsigned prepCommand[5] = {
-        50,
+        50,                     // Prepare sector(s) for write operation
-        flash_sector,
+        flash_sector,           // Start sector
-        flash_sector,
+        flash_sector,           // End sector
     };
     unsigned eraseCommand[5] = {
-        52,
+        52,                     // Erase sector(s)
-        flash_sector,
+        flash_sector,           // Start sector
-        flash_sector,
+        flash_sector,           // End sector
-        SystemCoreClock / 1000,
+        SystemCoreClock / 1000, // CPU clock frequency in kHz
     };
     unsigned writeCommand[5] = {
-        51,
+        51,                     // Copy RAM to Flash
-        flash_addr,
+        flash_addr,             // Destination flash address (256-byte boundary)
-        (unsigned)flash_buffer,
+        (unsigned)flash_buffer, // Source RAM address (word boundary)
-        flash_size,
+        flash_size,             // Number of bytes to write (must be: 256, 512, 1024, 4096)
-        SystemCoreClock / 1000,
+        SystemCoreClock / 1000, // CPU clock frequency in kHz
     };
     unsigned output[5];
+    // Run In-Application Programming (IAP) routines
     iap(prepCommand, output);
     iap(eraseCommand, output);
     iap(prepCommand, output);

grbl/config.h

@@ -125,7 +125,7 @@
 // #define HOMING_CYCLE_1 (1<<Y_AXIS)  // COREXY COMPATIBLE: Then home Y
 
 // Number of homing cycles performed after when the machine initially jogs to limit switches.
-// This help in preventing overshoot and should improve repeatability. This value should be one or
+// This helps in preventing overshoot and should improve repeatability. This value should be one or
 // greater.
 #define N_HOMING_LOCATE_CYCLE 1 // Integer (1-128)
 

grbl/cpu_map.h

@@ -63,7 +63,7 @@
   #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
+    #define Z_LIMIT_BIT    4 // Uno Digital Pin 12
   #else
     #define Z_LIMIT_BIT    3  // Uno Digital Pin 11
   #endif
@@ -96,9 +96,9 @@
   #define COOLANT_FLOOD_DDR   DDRC
   #define COOLANT_FLOOD_PORT  PORTC
   #define COOLANT_FLOOD_BIT   3  // Uno Analog Pin 3
-  #define COOLANT_MIST_DDR   DDRC
+  #define COOLANT_MIST_DDR    DDRC
-  #define COOLANT_MIST_PORT  PORTC
+  #define COOLANT_MIST_PORT   PORTC
-  #define COOLANT_MIST_BIT   4  // Uno Analog Pin 4
+  #define COOLANT_MIST_BIT    4  // Uno Analog Pin 4
 
   // Define user-control controls (cycle start, reset, feed hold) input pins.
   // NOTE: All CONTROLs pins must be on the same port and not on a port with other input pins (limits).
@@ -130,10 +130,10 @@
   #endif
   #define SPINDLE_PWM_OFF_VALUE     0
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	  TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	  TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
 
   // Prescaled, 8-bit Fast PWM mode.
   #define SPINDLE_TCCRA_INIT_MASK   ((1<<WGM20) | (1<<WGM21))  // Configures fast PWM mode.
@@ -143,11 +143,11 @@
   #define SPINDLE_TCCRB_INIT_MASK      (1<<CS22)               // 1/64 prescaler -> 0.98kHz (J-tech laser)
 
   // NOTE: On the 328p, these must be the same as the SPINDLE_ENABLE settings.
-  #define SPINDLE_PWM_DDR	  DDRB
+  #define SPINDLE_PWM_DDR     DDRB
   #define SPINDLE_PWM_PORT    PORTB
-  #define SPINDLE_PWM_BIT	  3    // Uno Digital Pin 11
+  #define SPINDLE_PWM_BIT     3    // Uno Digital Pin 11
 
-#endif
+#endif // end of CPU_MAP_ATMEGA328P
 
 
 #ifdef CPU_MAP_SMOOTHIEBOARD // (Smoothieboards)
@@ -190,7 +190,7 @@
   #define LIMIT_PORT        LPC_GPIO1->FIOPIN
   #define X_LIMIT_BIT       24  // X-MIN=24, X-MAX=25
   #define Y_LIMIT_BIT       26  // Y-MIN=26, Y-MAX=27
-  #define Z_LIMIT_BIT	    28  // Z-MIN=28, Z-MAX=29
+  #define Z_LIMIT_BIT       28  // Z-MIN=28, Z-MAX=29
   #define A_LIMIT_BIT       29  // reuse p1.29
   #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)|(1<<A_LIMIT_BIT)) // All limit bits
 
@@ -200,7 +200,7 @@
   #define COOLANT_FLOOD_BIT   4  // SMALL MOSFET Q8 (P2.4)
   #define COOLANT_MIST_DDR    LPC_GPIO2->FIODIR
   #define COOLANT_MIST_PORT   LPC_GPIO2->FIOPIN
-  #define COOLANT_MIST_BIT   6  // SMALL MOSFET Q9 (P2.6)
+  #define COOLANT_MIST_BIT    6  // SMALL MOSFET Q9 (P2.6)
   #define ENABLE_M7           // enables COOLANT MIST
 
   // Define user-control controls (cycle start, reset, feed hold) input pins.
@@ -252,11 +252,11 @@
   #endif
   //#define SPINDLE_PWM_OFF_VALUE     0 // Defined in config.h
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
-#endif
+#endif // end of CPU_MAP_SMOOTHIEBOARD
 
 
 #ifdef CPU_MAP_C3D_REMIX // (Cohesion3D Remix Boards)
@@ -299,7 +299,7 @@
   #define LIMIT_PORT        LPC_GPIO1->FIOPIN
   #define X_LIMIT_BIT       24  // X-MIN=24, X-MAX=25
   #define Y_LIMIT_BIT       26  // Y-MIN=26, Y-MAX=27
-  #define Z_LIMIT_BIT	    28  // Z-MIN=28, Z-MAX=29
+  #define Z_LIMIT_BIT       28  // Z-MIN=28, Z-MAX=29
   #define A_LIMIT_BIT       29  // reuse p1.29 from Z-MAX
   #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)|(1<<A_LIMIT_BIT)) // All limit bits
 
@@ -355,11 +355,11 @@
   #endif
   //#define SPINDLE_PWM_OFF_VALUE     0 // Defined in config.h
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
-#endif
+#endif // end of CPU_MAP_C3D_REMIX
 
 
 #ifdef CPU_MAP_C3D_MINI // (Cohesion3D Mini Boards)
@@ -402,7 +402,7 @@
   #define LIMIT_PORT        LPC_GPIO1->FIOPIN
   #define X_LIMIT_BIT       24  // X-MIN=24, X-MAX=25
   #define Y_LIMIT_BIT       26  // Y-MIN=26, Y-MAX=27
-  #define Z_LIMIT_BIT	    28  // Z-MIN=28, Z-MAX=29
+  #define Z_LIMIT_BIT       28  // Z-MIN=28, Z-MAX=29
   #define A_LIMIT_BIT       29  // reuse p1.29 from Z-MAX
   #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)|(1<<A_LIMIT_BIT)) // All limit bits
 
@@ -458,11 +458,11 @@
   #endif
   //#define SPINDLE_PWM_OFF_VALUE     0 // Defined in config.h
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
-#endif
+#endif // end of CPU_MAP_C3D_MINI
 
 
 #ifdef CPU_MAP_MKS_SBASE // (MKS SBASE Boards)
@@ -505,7 +505,7 @@
   #define LIMIT_PORT        LPC_GPIO1->FIOPIN
   #define X_LIMIT_BIT       24  // X-MIN=24, X-MAX=25
   #define Y_LIMIT_BIT       26  // Y-MIN=26, Y-MAX=27
-  #define Z_LIMIT_BIT	    28  // Z-MIN=28, Z-MAX=29
+  #define Z_LIMIT_BIT       28  // Z-MIN=28, Z-MAX=29
   #define A_LIMIT_BIT       29  // reuse p1.29
   #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)|(1<<A_LIMIT_BIT)) // All limit bits
 
@@ -573,11 +573,11 @@
   #endif
   //#define SPINDLE_PWM_OFF_VALUE     0 // Defined in config.h
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
-#endif
+#endif // end of CPU_MAP_MKS_SBASE
 
 
 #ifdef CPU_MAP_AZTEEG_X5 // (Azteeg X5 Boards)  not tested yet!
@@ -620,7 +620,7 @@
   #define LIMIT_PORT        LPC_GPIO1->FIOPIN
   #define X_LIMIT_BIT       24  // X-MIN=24, X-MAX=27
   #define Y_LIMIT_BIT       25  // Y-MIN=25, Y-MAX=28
-  #define Z_LIMIT_BIT	    26  // Z-MIN=26, Z-MAX=29
+  #define Z_LIMIT_BIT       26  // Z-MIN=26, Z-MAX=29
   #define A_LIMIT_BIT       27  // reuse p1.27, as X-MAX is not used
   #define LIMIT_MASK       ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)|(1<<A_LIMIT_BIT)) // All limit bits
 
@@ -678,11 +678,11 @@
   #endif
   //#define SPINDLE_PWM_OFF_VALUE     0 // Defined in config.h
   #define SPINDLE_PWM_RANGE         (SPINDLE_PWM_MAX_VALUE-SPINDLE_PWM_MIN_VALUE)
-  #define SPINDLE_TCCRA_REGISTER	TCCR2A
+  #define SPINDLE_TCCRA_REGISTER    TCCR2A
-  #define SPINDLE_TCCRB_REGISTER	TCCR2B
+  #define SPINDLE_TCCRB_REGISTER    TCCR2B
   #define SPINDLE_OCR_REGISTER      OCR2A
-  #define SPINDLE_COMB_BIT	        COM2A1
+  #define SPINDLE_COMB_BIT          COM2A1
-#endif
+#endif // end of CPU_MAP_AZTEEG_X5
 
 
 /*

grbl/defaults.h

@@ -77,7 +77,7 @@
   #define DEFAULT_SPINDLE_PWM_OFF_VALUE 0    // $34 % (% of PWM when spindle is off)
   #define DEFAULT_SPINDLE_PWM_MIN_VALUE 1    // $35 % (% of PWM when spindle is at lowest setting)
   #define DEFAULT_SPINDLE_PWM_MAX_VALUE 100  // $36 % (% of PWM when spindle is at highest setting)
-  // Up to 3 HOMING_CYCLE_x can be defined, specifying which axes are homed and in which order
+  // Up to 4 HOMING_CYCLE_x can be defined (0-3), specifying which axes are homed and in which order
   #define HOMING_CYCLE_0 ((1<<X_AXIS)|(1<<Y_AXIS))
 #endif // end of DEFAULTS_GENERIC
 

grbl/limits.c

@@ -158,9 +158,9 @@ void limits_go_home(uint8_t cycle_mask)
 
   // Initialize variables used for homing computations.
   uint8_t n_cycle = (2*N_HOMING_LOCATE_CYCLE+1);
-  uint32_t step_pin[N_AXIS];
+  uint32_t step_pin[N_AXIS]; // Tracks which pins correspond to which axes (reduces calls to get_step_pin_mask())
   float target[N_AXIS];
-  float max_travel = 0.0;
+  float max_travel = 0.0; // Maximum travel distance to move searching for limits
   uint8_t idx;
   for (idx=0; idx<N_AXIS; idx++) {
     // Initialize step pin masks
@@ -183,11 +183,12 @@ void limits_go_home(uint8_t cycle_mask)
   uint32_t limit_state, axislock, n_active_axis;
   do {
 
+    // convert current sys_position (steps) to target (mm) so unused axes remain in place
     system_convert_array_steps_to_mpos(target,sys_position);
 
     // Initialize and declare variables needed for homing routine.
-    axislock = 0;
+    axislock = 0; // Track which pins still need to find limits. Lock these axes by clearing these bits.
-    n_active_axis = 0;
+    n_active_axis = 0; // Track number of axes being homed
     for (idx=0; idx<N_AXIS; idx++) {
       // Set target location for active axes and setup computation for homing rate.
       if (bit_istrue(cycle_mask,bit(idx))) {
@@ -215,7 +216,7 @@ void limits_go_home(uint8_t cycle_mask)
           if (approach) { target[idx] = max_travel; }
           else { target[idx] = -max_travel; }
         }
-        // Apply axislock to the step port pins active in this cycle.
+        // Apply axislock to the step port pins active in this cycle, allowing motion
         axislock |= step_pin[idx];
       }
 
@@ -237,12 +238,13 @@ void limits_go_home(uint8_t cycle_mask)
         for (idx=0; idx<N_AXIS; idx++) {
           if (axislock & step_pin[idx]) {
             if (limit_state & (1 << idx)) {
-              #ifdef COREXY
+                // Clear the axislock bits to prevent axis from moving after limit is hit
-                if (idx==Z_AXIS) { axislock &= ~(step_pin[Z_AXIS]); }
+                #ifdef COREXY
-                else { axislock &= ~(step_pin[A_MOTOR]|step_pin[B_MOTOR]); }
+                  if (idx==Z_AXIS) { axislock &= ~(step_pin[Z_AXIS]); }
-              #else
+                  else { axislock &= ~(step_pin[A_MOTOR]|step_pin[B_MOTOR]); }
-                axislock &= ~(step_pin[idx]);
+                #else
-              #endif
+                  axislock &= ~(step_pin[idx]);
+                #endif
             }
           }
         }
@@ -297,7 +299,7 @@ void limits_go_home(uint8_t cycle_mask)
   // can be on either side of an axes, check and set axes machine zero appropriately. Also,
   // set up pull-off maneuver from axes limit switches that have been homed. This provides
   // some initial clearance off the switches and should also help prevent them from falsely
-  // triggering when hard limits are enabled or when more than one axes shares a limit pin.
+  // triggering when hard limits are enabled or when more than one axis shares a limit pin.
   int32_t set_axis_position;
   // Set machine positions for homed limit switches. Don't update non-homed axes.
   for (idx=0; idx<N_AXIS; idx++) {

grbl/main.c

@@ -42,13 +42,13 @@ int main(void)
 {
   // Initialize system upon power-up.
   debug_init();    // Initialize debug leds
-  isr_init();      // Set ISR priorities
+  isr_init();      // Set ISR priorities (stepper ISR uses Timer1)
-  delay_init();    // Setup delay timer
+  delay_init();    // Setup delay timer (uses Timer3)
   serial_init();   // Setup serial baud rate and interrupts
-  eeprom_init();   // Init EEPROM or FLASH
+  eeprom_init();   // Init EEPROM or Flash
   settings_init(); // Load Grbl settings from EEPROM
   current_init();  // Configure stepper driver current
-  stepper_init();  // Configure stepper pins and interrupt timers
+  stepper_init();  // Configure stepper pins and interrupt timers (uses Timer1)
   system_init();   // Configure pinout pins and pin-change interrupt
 
   memset(sys_position,0,sizeof(sys_position)); // Clear machine position.
@@ -84,26 +84,26 @@ int main(void)
     sys.f_override = DEFAULT_FEED_OVERRIDE;  // Set to 100%
     sys.r_override = DEFAULT_RAPID_OVERRIDE; // Set to 100%
     sys.spindle_speed_ovr = DEFAULT_SPINDLE_SPEED_OVERRIDE; // Set to 100%
-		memset(sys_probe_position,0,sizeof(sys_probe_position)); // Clear probe position.
+    memset(sys_probe_position,0,sizeof(sys_probe_position)); // Clear probe position.
-    sys_probe_state = 0;
+    sys_probe_state = 0;   // PROBE_OFF
-    sys_rt_exec_state = 0;
+    sys_rt_exec_state = 0; // EXEC_STATUS_REPORT
     sys_rt_exec_alarm = 0;
     sys_rt_exec_motion_override = 0;
     sys_rt_exec_accessory_override = 0;
 
     // Reset Grbl primary systems.
     serial_reset_read_buffer(); // Clear serial read buffer
-    gc_init(); // Set g-code parser to default state
+    gc_init();      // Set g-code parser to default state
-    spindle_init();
+    spindle_init(); // Configure spindle pins and PWM values
-    coolant_init();
+    coolant_init(); // Configure coolant pins
-    limits_init();
+    limits_init();  // Configure limit input pins and interrupts
-    probe_init();
+    probe_init();   // Configure probe input pin
-    plan_reset(); // Clear block buffer and planner variables
+    plan_reset();   // Clear block buffer and planner variables
-    st_reset(); // Clear stepper subsystem variables.
+    st_reset();     // Clear stepper subsystem variables.
 
     // Sync cleared gcode and planner positions to current system position.
-    plan_sync_position();
+    plan_sync_position(); // Synchronize plan position with (actual) system position
-    gc_sync_position();
+    gc_sync_position();   // Synchronize g-code position with (actual) system position
 
     // Print welcome message. Indicates an initialization has occured at power-up or with a reset.
     report_init_message();

grbl/settings.c

@@ -100,14 +100,14 @@ void settings_restore(uint8_t restore_flag) {
     settings.homing_pulloff = DEFAULT_HOMING_PULLOFF;
 
     settings.flags = 0;
-    if (DEFAULT_REPORT_INCHES) { settings.flags |= BITFLAG_REPORT_INCHES; }
+    if (DEFAULT_REPORT_INCHES)     { settings.flags |= BITFLAG_REPORT_INCHES;     }
-    if (DEFAULT_LASER_MODE) { settings.flags |= BITFLAG_LASER_MODE; }
+    if (DEFAULT_LASER_MODE)        { settings.flags |= BITFLAG_LASER_MODE;        }
-    if (DEFAULT_INVERT_ST_ENABLE) { settings.flags |= BITFLAG_INVERT_ST_ENABLE; }
+    if (DEFAULT_INVERT_ST_ENABLE)  { settings.flags |= BITFLAG_INVERT_ST_ENABLE;  }
     if (DEFAULT_HARD_LIMIT_ENABLE) { settings.flags |= BITFLAG_HARD_LIMIT_ENABLE; }
-    if (DEFAULT_HOMING_ENABLE) { settings.flags |= BITFLAG_HOMING_ENABLE; }
+    if (DEFAULT_HOMING_ENABLE)     { settings.flags |= BITFLAG_HOMING_ENABLE;     }
     if (DEFAULT_SOFT_LIMIT_ENABLE) { settings.flags |= BITFLAG_SOFT_LIMIT_ENABLE; }
     if (DEFAULT_INVERT_LIMIT_PINS) { settings.flags |= BITFLAG_INVERT_LIMIT_PINS; }
-    if (DEFAULT_INVERT_PROBE_PIN) { settings.flags |= BITFLAG_INVERT_PROBE_PIN; }
+    if (DEFAULT_INVERT_PROBE_PIN)  { settings.flags |= BITFLAG_INVERT_PROBE_PIN;  }
 
     settings.steps_per_mm[X_AXIS] = DEFAULT_X_STEPS_PER_MM;
     settings.steps_per_mm[Y_AXIS] = DEFAULT_Y_STEPS_PER_MM;
@@ -177,7 +177,7 @@ uint8_t settings_read_startup_line(uint8_t n, char *line)
   if (!(memcpy_from_eeprom_with_checksum((char*)line, addr, LINE_BUFFER_SIZE))) {
     // Reset line with default value
     line[0] = 0; // Empty line
-    settings_store_startup_line(n, line);
+    settings_store_startup_line(n, line); // Clear this startup line because it's corrupted
     return(false);
   }
   return(true);
@@ -190,7 +190,7 @@ uint8_t settings_read_build_info(char *line)
   if (!(memcpy_from_eeprom_with_checksum((char*)line, EEPROM_ADDR_BUILD_INFO, LINE_BUFFER_SIZE))) {
     // Reset line with default value
     line[0] = 0; // Empty line
-    settings_store_build_info(line);
+    settings_store_build_info(line); // Clear out build info string because it's corrupted
     return(false);
   }
   return(true);

grbl/settings.h

@@ -26,7 +26,7 @@
 
 
 // Version of the EEPROM data. Will be used to migrate existing data from older versions of Grbl
-// when firmware is upgraded. Always stored in byte 0 of eeprom
+// when firmware is upgraded. Always stored in byte 0 of EEPROM.
 #define SETTINGS_VERSION 11  // NOTE: Check settings_reset() when moving to next version.
 
 // Define bit flag masks for the boolean settings in settings.flag.
@@ -44,10 +44,10 @@
 #define BITFLAG_RT_STATUS_BUFFER_STATE      bit(1)
 
 // Define settings restore bitflags.
-#define SETTINGS_RESTORE_DEFAULTS bit(0)
+#define SETTINGS_RESTORE_DEFAULTS      bit(0)
-#define SETTINGS_RESTORE_PARAMETERS bit(1)
+#define SETTINGS_RESTORE_PARAMETERS    bit(1)
 #define SETTINGS_RESTORE_STARTUP_LINES bit(2)
-#define SETTINGS_RESTORE_BUILD_INFO bit(3)
+#define SETTINGS_RESTORE_BUILD_INFO    bit(3)
 #ifndef SETTINGS_RESTORE_ALL
   #define SETTINGS_RESTORE_ALL 0xFF // All bitflags
 #endif
@@ -56,6 +56,7 @@
 // NOTE: The Atmega328p has 1KB EEPROM. The upper half is reserved for parameters and
 // the startup script. The lower half contains the global settings and space for future
 // developments.
+// Note: Address 0 of EEPROM is reserved for SETTINGS_VERSION.
 #define EEPROM_ADDR_GLOBAL         1U
 #define EEPROM_ADDR_PARAMETERS     512U
 #define EEPROM_ADDR_STARTUP_BLOCK  768U
@@ -80,7 +81,7 @@ typedef struct {
   float steps_per_mm[N_AXIS];
   float max_rate[N_AXIS];
   float acceleration[N_AXIS];
-  float max_travel[N_AXIS];
+  float max_travel[N_AXIS];  // NOTE: Stored as a negative value
   float current[N_AXIS];
 
   // Remaining Grbl settings

grbl/stepper.c

@@ -30,10 +30,10 @@
 #define RAMP_DECEL 2
 #define RAMP_DECEL_OVERRIDE 3
 
-#define PREP_FLAG_RECALCULATE bit(0)
+#define PREP_FLAG_RECALCULATE        bit(0)
 #define PREP_FLAG_HOLD_PARTIAL_BLOCK bit(1)
-#define PREP_FLAG_PARKING bit(2)
+#define PREP_FLAG_PARKING            bit(2)
-#define PREP_FLAG_DECEL_OVERRIDE bit(3)
+#define PREP_FLAG_DECEL_OVERRIDE     bit(3)
 
 // Define Adaptive Multi-Axis Step-Smoothing(AMASS) levels and cutoff frequencies. The highest level
 // frequency bin starts at 0Hz and ends at its cutoff frequency. The next lower level frequency bin
@@ -45,11 +45,11 @@
 // NOTE: Current settings are set to overdrive the ISR to no more than 16kHz, balancing CPU overhead
 // and timer accuracy.  Do not alter these settings unless you know what you are doing.
 #ifdef ADAPTIVE_MULTI_AXIS_STEP_SMOOTHING
-	#define MAX_AMASS_LEVEL 3
+  #define MAX_AMASS_LEVEL 3
-	// AMASS_LEVEL0: Normal operation. No AMASS. No upper cutoff frequency. Starts at LEVEL1 cutoff frequency.
+  // AMASS_LEVEL0: Normal operation. No AMASS. No upper cutoff frequency. Starts at LEVEL1 cutoff frequency.
-	#define AMASS_LEVEL1 (F_CPU/8000) // Over-drives ISR (x2). Defined as F_CPU/(Cutoff frequency in Hz)
+  #define AMASS_LEVEL1 (F_CPU/8000) // Over-drives ISR (x2). Defined as F_CPU/(Cutoff frequency in Hz)
-	#define AMASS_LEVEL2 (F_CPU/4000) // Over-drives ISR (x4)
+  #define AMASS_LEVEL2 (F_CPU/4000) // Over-drives ISR (x4)
-	#define AMASS_LEVEL3 (F_CPU/2000) // Over-drives ISR (x8)
+  #define AMASS_LEVEL3 (F_CPU/2000) // Over-drives ISR (x8)
 
   #if MAX_AMASS_LEVEL <= 0
     error "AMASS must have 1 or more levels to operate correctly."
@@ -235,9 +235,9 @@ void st_wake_up()
   #endif
 
   // Enable Stepper Driver Interrupt Timer
-  LPC_TIM1->TCR = 0b10;   // reset
+  LPC_TIM1->TCR = 0b10;   // reset Timer Control (0b10=Reset, 0b01=Enable)
-  LPC_TIM1->MR0 = 4000;   // Generate first interrupt soon
+  LPC_TIM1->MR0 = 4000;   // Generate first interrupt soon (Match Register for TC)
-  LPC_TIM1->TCR = 0b01;   // enable
+  LPC_TIM1->TCR = 0b01;   // enable Timer Control (0b10=Reset, 0b01=Enable)
 }
 
 
@@ -245,11 +245,11 @@ void st_wake_up()
 void st_go_idle()
 {
   // Disable Stepper Driver Interrupt. Allow Stepper Port Reset Interrupt to finish, if active.
-  LPC_TIM1->TCR = 0;          // Disable Timer1
+  LPC_TIM1->TCR = 0;          // Disable Timer1 Control (0b10=Reset, 0b01=Enable)
   busy = false;
 
   // Set stepper driver idle state, disabled or enabled, depending on settings and circumstances.
-  bool pin_state = false; // Keep enabled.
+  bool pin_state = false; // Stepper is disabled when pin_state is true. Keep enabled by default.
   if (((settings.stepper_idle_lock_time != 0xff) || sys_rt_exec_alarm || sys.state == STATE_SLEEP) && sys.state != STATE_HOMING) {
     // Force stepper dwell to lock axes for a defined amount of time to ensure the axes come to a complete
     // stop and not drift from residual inertial forces at the end of the last movement.
@@ -355,7 +355,7 @@ extern "C" void TIMER1_IRQHandler()
       #endif
 
       // Initialize step segment timing per step and load number of steps to execute.
-      LPC_TIM1->MR0 = st.exec_segment->cycles_per_tick;
+      LPC_TIM1->MR0 = st.exec_segment->cycles_per_tick;  // Set Match Register to wait one tick
       st.step_count = st.exec_segment->n_step; // NOTE: Can sometimes be zero when moving slow.
       // If the new segment starts a new planner block, initialize stepper variables and counters.
       // NOTE: When the segment data index changes, this indicates a new planner block.
@@ -570,17 +570,17 @@ void st_reset()
 void stepper_init()
 {
   // Configure step and direction interface pins
-  STEP_DDR |= STEP_MASK;
+  STEP_DDR |= STEP_MASK;                         // Set selected stepper step pins as outputs
-  STEPPERS_DISABLE_DDR |= STEPPERS_DISABLE_MASK;
+  STEPPERS_DISABLE_DDR |= STEPPERS_DISABLE_MASK; // Set selected stepper disable pins as outputs
-  DIRECTION_DDR |= DIRECTION_MASK;
+  DIRECTION_DDR |= DIRECTION_MASK;               // Set selected stepper direction pins as outputs
 
   // Configure Timer 1: Stepper Driver Interrupt
-  LPC_TIM1->TCR = 0;            // disable
+  LPC_TIM1->TCR = 0;            // disable Timer Control (0b10=Reset, 0b01=Enable)
-  LPC_TIM1->CTCR = 0;           // timer mode
+  LPC_TIM1->CTCR = 0;           // Count Control (0=TimerMode, 1-3=EdgeCounterMode)
-  LPC_TIM1->PR = 0;             // no prescale
+  LPC_TIM1->PR = 0;             // no Prescale (TC increments every PR+1 clocks)
-  LPC_TIM1->MCR = 0b011;        // MR0: !stop, reset, interrupt
+  LPC_TIM1->MCR = 0b011;        // Match Control (0b001=InterruptEnbl, 0b010=Reset_Enbl, 0b100=Stop_Enbl)
-  LPC_TIM1->CCR = 0;            // no capture
+  LPC_TIM1->CCR = 0;            // no Capture Control actions
-  LPC_TIM1->EMR = 0;            // no external match
+  LPC_TIM1->EMR = 0;            // no External Match (controls external match pins)
   NVIC_EnableIRQ(TIMER1_IRQn);  // Enable Stepper Driver Interrupt
 }
 
@@ -732,34 +732,34 @@ void st_prep_buffer()
         #endif
       }
 
-			/* ---------------------------------------------------------------------------------
+      /* ---------------------------------------------------------------------------------
-			 Compute the velocity profile of a new planner block based on its entry and exit
+       Compute the velocity profile of a new planner block based on its entry and exit
-			 speeds, or recompute the profile of a partially-completed planner block if the
+       speeds, or recompute the profile of a partially-completed planner block if the
-			 planner has updated it. For a commanded forced-deceleration, such as from a feed
+       planner has updated it. For a commanded forced-deceleration, such as from a feed
-			 hold, override the planner velocities and decelerate to the target exit speed.
+       hold, override the planner velocities and decelerate to the target exit speed.
-			*/
+      */
-			prep.mm_complete = 0.0; // Default velocity profile complete at 0.0mm from end of block.
+      prep.mm_complete = 0.0; // Default velocity profile complete at 0.0mm from end of block.
-			float inv_2_accel = 0.5/pl_block->acceleration;
+      float inv_2_accel = 0.5/pl_block->acceleration;
-			if (sys.step_control & STEP_CONTROL_EXECUTE_HOLD) { // [Forced Deceleration to Zero Velocity]
+      if (sys.step_control & STEP_CONTROL_EXECUTE_HOLD) { // [Forced Deceleration to Zero Velocity]
-				// Compute velocity profile parameters for a feed hold in-progress. This profile overrides
+        // Compute velocity profile parameters for a feed hold in-progress. This profile overrides
-				// the planner block profile, enforcing a deceleration to zero speed.
+        // the planner block profile, enforcing a deceleration to zero speed.
-				prep.ramp_type = RAMP_DECEL;
+        prep.ramp_type = RAMP_DECEL;
-				// Compute decelerate distance relative to end of block.
+        // Compute decelerate distance relative to end of block.
-				float decel_dist = pl_block->millimeters - inv_2_accel*pl_block->entry_speed_sqr;
+        float decel_dist = pl_block->millimeters - inv_2_accel*pl_block->entry_speed_sqr;
-				if (decel_dist < 0.0) {
+        if (decel_dist < 0.0) {
-					// Deceleration through entire planner block. End of feed hold is not in this block.
+          // Deceleration through entire planner block. End of feed hold is not in this block.
-					prep.exit_speed = sqrt(pl_block->entry_speed_sqr-2*pl_block->acceleration*pl_block->millimeters);
+          prep.exit_speed = sqrt(pl_block->entry_speed_sqr-2*pl_block->acceleration*pl_block->millimeters);
-				} else {
+        } else {
-					prep.mm_complete = decel_dist; // End of feed hold.
+          prep.mm_complete = decel_dist; // End of feed hold.
-					prep.exit_speed = 0.0;
+          prep.exit_speed = 0.0;
-				}
+        }
-			} else { // [Normal Operation]
+      } else { // [Normal Operation]
-				// Compute or recompute velocity profile parameters of the prepped planner block.
+        // Compute or recompute velocity profile parameters of the prepped planner block.
-				prep.ramp_type = RAMP_ACCEL; // Initialize as acceleration ramp.
+        prep.ramp_type = RAMP_ACCEL; // Initialize as acceleration ramp.
-				prep.accelerate_until = pl_block->millimeters;
+        prep.accelerate_until = pl_block->millimeters;
 
-				float exit_speed_sqr;
+        float exit_speed_sqr;
-				float nominal_speed;
+        float nominal_speed;
         if (sys.step_control & STEP_CONTROL_EXECUTE_SYS_MOTION) {
           prep.exit_speed = exit_speed_sqr = 0.0; // Enforce stop at end of system motion.
         } else {
@@ -768,9 +768,9 @@ void st_prep_buffer()
         }
 
         nominal_speed = plan_compute_profile_nominal_speed(pl_block);
-				float nominal_speed_sqr = nominal_speed*nominal_speed;
+        float nominal_speed_sqr = nominal_speed*nominal_speed;
-				float intersect_distance =
+        float intersect_distance =
-								0.5*(pl_block->millimeters+inv_2_accel*(pl_block->entry_speed_sqr-exit_speed_sqr));
+                0.5*(pl_block->millimeters+inv_2_accel*(pl_block->entry_speed_sqr-exit_speed_sqr));
 
         if (pl_block->entry_speed_sqr > nominal_speed_sqr) { // Only occurs during override reductions.
           prep.accelerate_until = pl_block->millimeters - inv_2_accel*(pl_block->entry_speed_sqr-nominal_speed_sqr);
@@ -793,35 +793,35 @@ void st_prep_buffer()
             prep.maximum_speed = nominal_speed;
             prep.ramp_type = RAMP_DECEL_OVERRIDE;
           }
-				} else if (intersect_distance > 0.0) {
+        } else if (intersect_distance > 0.0) {
-					if (intersect_distance < pl_block->millimeters) { // Either trapezoid or triangle types
+          if (intersect_distance < pl_block->millimeters) { // Either trapezoid or triangle types
-						// NOTE: For acceleration-cruise and cruise-only types, following calculation will be 0.0.
+            // NOTE: For acceleration-cruise and cruise-only types, following calculation will be 0.0.
-						prep.decelerate_after = inv_2_accel*(nominal_speed_sqr-exit_speed_sqr);
+            prep.decelerate_after = inv_2_accel*(nominal_speed_sqr-exit_speed_sqr);
-						if (prep.decelerate_after < intersect_distance) { // Trapezoid type
+            if (prep.decelerate_after < intersect_distance) { // Trapezoid type
-							prep.maximum_speed = nominal_speed;
+              prep.maximum_speed = nominal_speed;
-							if (pl_block->entry_speed_sqr == nominal_speed_sqr) {
+              if (pl_block->entry_speed_sqr == nominal_speed_sqr) {
-								// Cruise-deceleration or cruise-only type.
+                // Cruise-deceleration or cruise-only type.
-								prep.ramp_type = RAMP_CRUISE;
+                prep.ramp_type = RAMP_CRUISE;
-							} else {
+              } else {
-								// Full-trapezoid or acceleration-cruise types
+                // Full-trapezoid or acceleration-cruise types
-								prep.accelerate_until -= inv_2_accel*(nominal_speed_sqr-pl_block->entry_speed_sqr);
+                prep.accelerate_until -= inv_2_accel*(nominal_speed_sqr-pl_block->entry_speed_sqr);
-							}
+              }
-						} else { // Triangle type
+            } else { // Triangle type
-							prep.accelerate_until = intersect_distance;
+              prep.accelerate_until = intersect_distance;
-							prep.decelerate_after = intersect_distance;
+              prep.decelerate_after = intersect_distance;
-							prep.maximum_speed = sqrt(2.0*pl_block->acceleration*intersect_distance+exit_speed_sqr);
+              prep.maximum_speed = sqrt(2.0*pl_block->acceleration*intersect_distance+exit_speed_sqr);
-						}
+            }
-					} else { // Deceleration-only type
+          } else { // Deceleration-only type
             prep.ramp_type = RAMP_DECEL;
             // prep.decelerate_after = pl_block->millimeters;
             // prep.maximum_speed = prep.current_speed;
-					}
+          }
-				} else { // Acceleration-only type
+        } else { // Acceleration-only type
-					prep.accelerate_until = 0.0;
+          prep.accelerate_until = 0.0;
-					// prep.decelerate_after = 0.0;
+          // prep.decelerate_after = 0.0;
-					prep.maximum_speed = prep.exit_speed;
+          prep.maximum_speed = prep.exit_speed;
-				}
+        }
-			}
+      }
 
       #ifdef VARIABLE_SPINDLE
         bit_true(sys.step_control, STEP_CONTROL_UPDATE_SPINDLE_PWM); // Force update whenever updating block.

grbl/system.c

@@ -23,14 +23,15 @@
 
 void system_init()
 {
+  // Configure user control pins (for cycle start, reset, feed hold, etc.)
   CONTROL_DDR &= ~(CONTROL_MASK); // Configure as input pins
   #ifdef DISABLE_CONTROL_PIN_PULL_UP
     CONTROL_PORT &= ~(CONTROL_MASK); // Normal low operation. Requires external pull-down.
   #else
-    CONTROL_PORT |= CONTROL_MASK;   // Enable internal pull-up resistors. Normal high operation.
+    CONTROL_PORT |= CONTROL_MASK;    // Enable internal pull-up resistors. Normal high operation.
   #endif
-  CONTROL_PCMSK |= CONTROL_MASK;  // Enable specific pins of the Pin Change Interrupt
+  CONTROL_PCMSK |= CONTROL_MASK;     // Enable specific pins of the Pin Change Interrupt
-  PCICR |= (1 << CONTROL_INT);   // Enable Pin Change Interrupt
+  PCICR |= (1 << CONTROL_INT);       // Enable Pin Change Interrupt
 }
 
 
@@ -195,7 +196,7 @@ uint8_t system_execute_line(char *line)
           if (!sys.abort) {  // Execute startup scripts after successful homing.
             sys.state = STATE_IDLE; // Set to IDLE when complete.
             st_go_idle(); // Set steppers to the settings idle state before returning.
-            if (line[2] == 0) { system_execute_startup(line); }
+            if (line[2] == 0) { system_execute_startup(line); } // Execute startup script again.
           }
           break;
         case 'S' : // Puts Grbl to sleep [IDLE/ALARM]