Re-factored system states and alarm management. Serial baud support greater than 57600.

- Refactored system states to be more clear and concise. Alarm locks
processes when position is unknown to indicate to user something has
gone wrong.

- Changed mc_alarm to mc_reset, which now manages the system reset
function. Centralizes it.

- Renamed '$X' kill homing lock to kill alarm lock.

- Created an alarm error reporting method to clear up what is an alarm:
message vs a status error: message. For GUIs mainly. Alarm codes are
negative. Status codes are positive.

- Serial baud support upto 115200. Previous baudrate calc was unstable
for 57600 and above.

- Alarm state locks out all g-code blocks, including startup scripts,
but allows user to access settings and internal commands. For example,
to disable hard limits, if they are problematic.

- Hard limits do not respond in an alarm state.

- Fixed a problem with the hard limit interrupt during the homing
cycle. The interrupt register is still active during the homing cycle
and still signal the interrupt to trigger when re-enabled. Instead,
just disabled the register.

- Homing rate adjusted. All axes move at homing seek rate, regardless
of how many axes move at the same time. This is unlike how the stepper
module does it as a point to point rate.

- New config.h settings to disable the homing rate adjustment and the
force homing upon powerup.

- Reduced the number of startup lines back down to 2 from 3. This
discourages users from placing motion block in there, which can be very
dangerous.

- Startup blocks now run only after an alarm-free reset or after a
homing cycle. Does not run when $X kill is called. For satefy reasons

nuts_bolts.h

@@ -63,31 +63,29 @@
 #define EXEC_FEED_HOLD      bit(3) // bitmask 00001000
 #define EXEC_RESET          bit(4) // bitmask 00010000
 #define EXEC_ALARM          bit(5) // bitmask 00100000
-// #define                  bit(6) // bitmask 01000000
+#define EXEC_CRIT_EVENT     bit(6) // bitmask 01000000
 // #define                  bit(7) // bitmask 10000000
 
 // Define system state bit map. The state variable primarily tracks the individual functions
 // of Grbl to manage each without overlapping. It is also used as a messaging flag for
 // critical events.
 #define STATE_IDLE   0 // Must be zero.
-#define STATE_QUEUED 1 // Indicates buffered blocks, awaiting cycle start.
-#define STATE_CYCLE  2 // Cycle is running
-#define STATE_HOLD   3 // Executing feed hold
-#define STATE_HOMING 4 // Performing homing cycle
-#define STATE_JOG    5 // Jogging mode is unique like homing.
-#define STATE_ALARM  6 // In alarm state. Locks out all g-code processes and messages position lost
-#define STATE_LIMIT  7 // Used to message hard limit triggered.
+#define STATE_INIT   1 // Initial power up state.
+#define STATE_QUEUED 2 // Indicates buffered blocks, awaiting cycle start.
+#define STATE_CYCLE  3 // Cycle is running
+#define STATE_HOLD   4 // Executing feed hold
+#define STATE_HOMING 5 // Performing homing cycle
+#define STATE_ALARM  6 // In alarm state. Locks out all g-code processes. Allows settings access.
+// #define STATE_JOG    7 // Jogging mode is unique like homing.
 
 // Define global system variables
 typedef struct {
   uint8_t abort;                 // System abort flag. Forces exit back to main loop for reset.
   uint8_t state;                 // Tracks the current state of Grbl.
   volatile uint8_t execute;      // Global system runtime executor bitflag variable. See EXEC bitmasks.
-  int32_t position[3];           // Real-time machine (aka home) position vector in steps. 
+  int32_t position[N_AXIS];      // Real-time machine (aka home) position vector in steps. 
                                  // NOTE: This may need to be a volatile variable, if problems arise.   
   uint8_t auto_start;            // Planner auto-start flag. Toggled off during feed hold. Defaulted by settings.
-//   uint8_t feed_hold;             // Feed hold flag. Held true during feed hold. Released when ready to resume.
-//   volatile uint8_t cycle_start;  // Cycle start flag. Set by stepper subsystem or main program. 
 } system_t;
 extern system_t sys;