Hard limits code minor updates.

- Fixed a bug that would not disable the steppers if a user issues a
system abort during a homing cycle.

- Updated the hard limit interrupt to be more correct and to issue a
shutdown for the right situations when the switch has been triggered.

- Added a status message to indicate to the user what happened and what
to do upon a hard limit trigger.

config.h

@@ -46,9 +46,9 @@
 #define X_LIMIT_BIT     1  // Uno Digital Pin 9
 #define Y_LIMIT_BIT     2  // Uno Digital Pin 10
 #define Z_LIMIT_BIT     3  // Uno Digital Pin 11
-#define LIMIT_INT       PCIE0  // Pin change interrupt settings
-#define LIMIT_INT_vect  PCINT0_vect
-#define LIMIT_PCMSK     PCMSK0
+#define LIMIT_INT       PCIE0  // Pin change interrupt enable pin
+#define LIMIT_INT_vect  PCINT0_vect 
+#define LIMIT_PCMSK     PCMSK0 // Pin change interrupt register
 
 #define SPINDLE_ENABLE_DDR   DDRB
 #define SPINDLE_ENABLE_PORT  PORTB

limits.c

@@ -39,27 +39,34 @@ void limits_init()
   LIMIT_DDR &= ~(LIMIT_MASK); // Set as input pins
   LIMIT_PORT |= (LIMIT_MASK); // Enable internal pull-up resistors. Normal high operation.
 
-  if bit_istrue(settings.flags,BITFLAG_HARD_LIMIT_ENABLE) {
-    MCUCR = (1<<ISC01) | (0<<ISC00); //1 0 triggers at a falling edge.
+  if (bit_istrue(settings.flags,BITFLAG_HARD_LIMIT_ENABLE)) {
     LIMIT_PCMSK |= LIMIT_MASK;   // Enable specific pins of the Pin Change Interrupt
     PCICR |= (1 << LIMIT_INT);   // Enable Pin Change Interrupt
   }
 }
 
-// This is the Limit Pin Change Interrupt, which handles the hard limit feature. This is
-// called when Grbl detects a falling edge on a limit pin.
+// This is the Limit Pin Change Interrupt, which handles the hard limit feature.
 // NOTE: Do not attach an e-stop to the limit pins, because this interrupt is disabled during
 // homing cycles and will not respond correctly. Upon user request or need, there may be a
 // special pinout for an e-stop, but it is generally recommended to just directly connect
 // your e-stop switch to the Arduino reset pin, since it is the most correct way to do this.
 ISR(LIMIT_INT_vect) 
 {
-  // Kill all processes upon hard limit event.
-  st_go_idle(); // Immediately stop stepper motion
-  spindle_stop(); // Stop spindle
-  sys.auto_start = false; // Disable auto cycle start.
-  sys.execute |= EXEC_ALARM;
-  // TODO: When Grbl system status is installed, update here to indicate loss of position.
+  // Only enter if the system alarm is not active.
+  if (bit_isfalse(sys.execute,EXEC_ALARM)) { 
+    // Kill all processes upon hard limit event.
+    if ((LIMIT_PIN & LIMIT_MASK) ^ LIMIT_MASK) {
+      st_go_idle(); // Immediately stop stepper motion
+      spindle_stop(); // Stop spindle
+      sys.auto_start = false; // Disable auto cycle start.
+      sys.execute |= EXEC_ALARM;
+      // TODO: When Grbl system status is installed, update here to indicate loss of position.
+    } 
+    // else {
+    //   TODO: When leaving a switch, this interrupt can be activated upon detecting a pin
+    //   change to high. If so, need to start a countdown timer to check the pin again after
+    //   a debounce period to not falsely re-engage the alarm.
+  }
 }
 
 

motion_control.c

@@ -217,7 +217,7 @@ void mc_go_home()
     if (bit_istrue(settings.homing_dir_mask,bit(Z_DIRECTION_BIT))) { z_dir = -1; }
     mc_line(x_dir*settings.homing_pulloff, y_dir*settings.homing_pulloff, 
             z_dir*settings.homing_pulloff, settings.homing_feed_rate, false);
-    st_cycle_start(); // Nothing should be in the buffer except this motion. 
+    st_cycle_start(); // Move it. Nothing should be in the buffer except this motion. 
     plan_synchronize(); // Make sure the motion completes.
     gc_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
     PCICR |= (1 << LIMIT_INT);  // Re-enable hard limits.

nuts_bolts.h

@@ -80,8 +80,6 @@ typedef struct {
   uint8_t abort;                 // System abort flag. Forces exit back to main loop for reset.
   uint8_t feed_hold;             // Feed hold flag. Held true during feed hold. Released when ready to resume.
   uint8_t auto_start;            // Planner auto-start flag. Toggled off during feed hold. Defaulted by settings.
-  uint8_t alarm;                 // Alarm mode. Causes all functions to immediately cease until a system abort
-                                 // is issued by the user.
 //   uint8_t switches;              // Switches state bitflag variable. For settings not governed by g-code.
   
   int32_t position[3];           // Real-time machine (aka home) position vector in steps. 

protocol.c

@@ -57,6 +57,8 @@ void protocol_status_message(int8_t status_code)
       printPgmString(PSTR("Invalid command\r\n")); break;
       case STATUS_SETTING_DISABLED:
       printPgmString(PSTR("Grbl setting disabled\r\n")); break;
+      case STATUS_HARD_LIMIT:
+      printPgmString(PSTR("Limit triggered <Check and Reset>\r\n")); break;
       default:
       printInteger(status_code);
       printPgmString(PSTR("\r\n"));
@@ -141,6 +143,7 @@ void protocol_execute_runtime()
     
     // System alarm. Something has gone wrong. Disable everything until system reset.
     if (rt_exec & EXEC_ALARM) {
+      protocol_status_message(STATUS_HARD_LIMIT);
       while (bit_isfalse(sys.execute,EXEC_RESET)) { sleep_mode(); }
       bit_false(sys.execute,EXEC_ALARM);
     } 

protocol.h

@@ -29,6 +29,7 @@
 #define STATUS_MODAL_GROUP_VIOLATION 5
 #define STATUS_INVALID_COMMAND 6
 #define STATUS_SETTING_DISABLED 7
+#define STATUS_HARD_LIMIT 8
 
 #define LINE_BUFFER_SIZE 50
 

serial.c

@@ -166,7 +166,7 @@ ISR(USART_RX_vect)
     case CMD_CYCLE_START:   sys.execute |= EXEC_CYCLE_START; break; // Set as true
     case CMD_FEED_HOLD:     sys.execute |= EXEC_FEED_HOLD; break; // Set as true
     case CMD_RESET:
-      sys.alarm |= EXEC_ALARM; // Set alarm to allow subsystem disable for certain settings.
+      sys.execute |= EXEC_ALARM; // Set alarm to allow subsystem disable for certain settings.
       
       // TODO: When Grbl system status is installed, set position lost state if the cycle is active.