Marked a large number of non-critical functions with FLASHMEM to save RAM for the iMXRT1062 driver.

Improved alarm handling, if a critical alarm is active when a non-critical alarm is raised the non-critical alarm will be delayed until after reset for the critical alarm.
Improved Modbus exception handling and added high level API call for creating and sending Modbus messages.
Added G65P7 inbuilt macro for interacting with Modbus devices from gcode. See the Wiki for details.

machine_limits.c

@@ -113,7 +113,7 @@ ISR_CODE void ISR_FUNC(limit_interrupt_handler)(limit_signals_t state) // DEFAUL
 
 // Establish work envelope for homed axes, used by soft limits and jog limits handling.
 // When hard limits are enabled pulloff distance is subtracted to avoid triggering limit switches.
-void limits_set_work_envelope (void)
+FLASHMEM void limits_set_work_envelope (void)
 {
     uint_fast8_t idx = N_AXIS;
 
@@ -143,7 +143,7 @@ void limits_set_work_envelope (void)
 
 // Set machine positions for homed limit switches. Don't update non-homed axes.
 // NOTE: settings.max_travel[] is stored as a negative value.
-void limits_set_machine_positions (axes_signals_t cycle, bool add_pulloff)
+FLASHMEM void limits_set_machine_positions (axes_signals_t cycle, bool add_pulloff)
 {
     uint_fast8_t idx = N_AXIS;
 
@@ -167,7 +167,7 @@ void limits_set_machine_positions (axes_signals_t cycle, bool add_pulloff)
 #endif
 
 // Set, get homing pulloff
-coord_data_t *limits_homing_pulloff (coord_data_t *distance)
+FLASHMEM coord_data_t *limits_homing_pulloff (coord_data_t *distance)
 {
     if(distance)
         memcpy(&homing_pulloff, distance, sizeof(coord_data_t));
@@ -177,7 +177,7 @@ coord_data_t *limits_homing_pulloff (coord_data_t *distance)
 
 // Pulls off axes from asserted homing switches before homing starts.
 // For now only for auto squared axes.
-static bool limits_pull_off (axes_signals_t axis, coord_data_t *distance, float scaling)
+FLASHMEM static bool limits_pull_off (axes_signals_t axis, coord_data_t *distance, float scaling)
 {
     uint_fast8_t n_axis = 0, idx = N_AXIS;
     coord_data_t target = {0};
@@ -266,7 +266,7 @@ static bool limits_pull_off (axes_signals_t axis, coord_data_t *distance, float
 // mask, which prevents the stepper algorithm from executing step pulses. Homing motions typically
 // circumvent the processes for executing motions in normal operation.
 // NOTE: Only the abort realtime command can interrupt this process.
-static bool homing_cycle (axes_signals_t cycle, axes_signals_t auto_square)
+FLASHMEM static bool homing_cycle (axes_signals_t cycle, axes_signals_t auto_square)
 {
     if (ABORTED) // Block if system reset has been issued.
         return false;
@@ -532,7 +532,7 @@ static bool homing_cycle (axes_signals_t cycle, axes_signals_t auto_square)
 
 // Perform homing cycle(s) according to configuration.
 // NOTE: only one auto squared axis can be homed at a time.
-status_code_t limits_go_home (axes_signals_t cycle)
+FLASHMEM status_code_t limits_go_home (axes_signals_t cycle)
 {
     axes_signals_t auto_square = {0}, auto_squared = {0};
 
@@ -604,7 +604,7 @@ status_code_t limits_go_home (axes_signals_t cycle)
 // Performs a soft limit check. Called from mc_line() only. Assumes the machine has been homed,
 // the workspace volume is in all negative space, and the system is in normal operation.
 // NOTE: Also used by jogging to block travel outside soft-limit volume.
-void limits_soft_check (float *target, planner_cond_t condition)
+FLASHMEM void limits_soft_check (float *target, planner_cond_t condition)
 {
 #ifdef KINEMATICS_API
     if(condition.target_validated ? !condition.target_valid : !grbl.check_travel_limits(target, sys.soft_limits, false, &sys.work_envelope)) {
@@ -630,7 +630,7 @@ void limits_soft_check (float *target, planner_cond_t condition)
 }
 
 // Set axes to be homed from settings.
-void limits_set_homing_axes (void)
+FLASHMEM void limits_set_homing_axes (void)
 {
     uint_fast8_t idx = N_AXIS;
 
@@ -644,7 +644,7 @@ void limits_set_homing_axes (void)
 }
 
 // Check if homing is required.
-bool limits_homing_required (void)
+FLASHMEM bool limits_homing_required (void)
 {
     return settings.homing.flags.enabled && settings.homing.flags.init_lock &&
             (sys.cold_start || !settings.homing.flags.override_locks) &&
@@ -652,7 +652,7 @@ bool limits_homing_required (void)
 }
 
 // Get homing rate from the first axis in the cycle.
-static float get_homing_rate (axes_signals_t cycle, homing_mode_t mode)
+FLASHMEM static float get_homing_rate (axes_signals_t cycle, homing_mode_t mode)
 {
     uint_fast8_t idx = 0;
 
@@ -845,7 +845,7 @@ static void apply_travel_limits (float *target, float *position, work_envelope_t
     } while(idx);
 }
 
-void limits_init (void)
+FLASHMEM void limits_init (void)
 {
     hal.homing.get_feedrate = get_homing_rate;
     grbl.check_travel_limits = check_travel_limits;