Minor updates, improvements, and bug fixes.

- Allowed status_message function to be called by others. This is to
centralize all feedback into protocol.c.

- Fixed a bug where line number words 'N' were causing the parser to
error out.

- Allowed homing routine feed rates to move slower than the
MINIMUM_STEP_RATE parameter in config.h.

- Homing performs idle lock at the end of the routine.

- Stepper idle lock time will now not disable the steppers when the
value is set at 255. This is accomodate users who prefer to keep their
axes enabled at all times.

- Moved some defines around to where they need to be.

limits.c

@@ -30,6 +30,7 @@
 #include "motion_control.h"
 #include "planner.h"
 #include "protocol.h"
+#include "limits.h"
 
 #define MICROSECONDS_PER_ACCELERATION_TICK  (1000000/ACCELERATION_TICKS_PER_SECOND)
 
@@ -76,9 +77,11 @@ static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, int8_t pos_dir,
   
   // Nominal and initial time increment per step. Nominal should always be greater then 3
   // usec, since they are based on the same parameters as the main stepper routine. Initial
-  // is based on the MINIMUM_STEPS_PER_MINUTE config.
+  // is based on the MINIMUM_STEPS_PER_MINUTE config. Since homing feed can be very slow,
+  // disable acceleration when rates are below MINIMUM_STEPS_PER_MINUTE.
   uint32_t dt_min = lround(1000000*60/(ds*homing_rate)); // Cruising (usec/step)
   uint32_t dt = 1000000*60/MINIMUM_STEPS_PER_MINUTE; // Initial (usec/step)
+  if (dt > dt_min) { dt = dt_min; } // Disable acceleration for very slow rates.
       
   // Set default out_bits. 
   uint8_t out_bits0 = settings.invert_mask;
@@ -164,8 +167,8 @@ void limits_go_home()
   STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT);
   
   // Jog all axes toward home to engage their limit switches at faster homing seek rate.
-  homing_cycle(false, false, true, true, false, settings.homing_seek_rate); // First jog the z axis
-  homing_cycle(true, true, false, true, false, settings.homing_seek_rate);   // Then jog the x and y axis
+  homing_cycle(false, false, true, true, false, settings.homing_seek_rate);  // First jog the z axis
+  homing_cycle(true, true, false, true, false, settings.homing_seek_rate);  // Then jog the x and y axis
   delay_ms(settings.homing_debounce_delay); // Delay to debounce signal
     
   // Now in proximity of all limits. Carefully leave and approach switches in multiple cycles
@@ -183,6 +186,9 @@ void limits_go_home()
     }
   }
 
+  delay_ms(settings.stepper_idle_lock_time);
   // Disable steppers by setting stepper disable
-  STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT);
+  if (settings.stepper_idle_lock_time != 0xff) {
+    STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT);
+  }
 }