Settings refactoring. Bug fixes. Misc new features.

This is likely the last major change to the v0.9 code base before push
to master. Only two minor things remain on the agenda (CoreXY support,
force clear EEPROM, and an extremely low federate bug).

- NEW! Grbl is now compile-able and may be flashed directly through the
Arduino IDE. Only minor changes were required for this compatibility.
See the Wiki to learn how to do it.

- New status reporting mask to turn on and off what Grbl sends back.
This includes machine coordinates, work coordinates, serial RX buffer
usage, and planner buffer usage. Expandable to more information on user
request, but that’s it for now.

- Settings have been completely renumbered to allow for future new
settings to be installed without having to constantly reshuffle and
renumber all of the settings every time.

- All settings masks have been standardized to mean bit 0 = X, bit 1 =
Y, and bit 2 = Z, to reduce confusion on how they work. The invert
masks used by the internal Grbl system were updated to accommodate this
change as well.

- New invert probe pin setting, which does what it sounds like.

- Fixed a probing cycle bug, where it would freeze intermittently, and
removed some redundant code.

- Homing may now be set to the origin wherever the limit switches are.
Traditionally machine coordinates should always be in negative space,
but when limit switches on are on the opposite side, the machine
coordinate would be set to -max_travel for the axis. Now you can always
make it [0,0,0] via a compile-time option in config.h. (Soft limits
routine was updated to account for this as well.)

 - Probe coordinate message immediately after a probing cycle may now
be turned off via a compile-time option in config.h. By default the
probing location is always reported.

- Reduced the N_ARC_CORRECTION default value to reflect the changes in
how circles are generated by an arc tolerance, rather than a fixed arc
segment setting.

- Increased the incoming line buffer limit from 70 to 80 characters.
Had some extra memory space to invest into this.

- Fixed a bug where tool number T was not being tracked and reported
correctly.

- Added a print free memory function for debugging purposes. Not used
otherwise.

- Realtime rate report should now work during feed holds, but it hasn’t
been tested yet.

- Updated the streaming scripts with MIT-license and added the simple
streaming to the main stream.py script to allow for settings to be sent.

- Some minor code refactoring to improve flash efficiency. Reduced the
flash by several hundred KB, which was re-invested in some of these new
features.

stepper.c

@@ -109,6 +109,10 @@ static volatile uint8_t segment_buffer_tail;
 static uint8_t segment_buffer_head;
 static uint8_t segment_next_head;
 
+// Step and direction port invert masks. 
+static uint8_t step_port_invert_mask;
+static uint8_t dir_port_invert_mask;
+
 // Used to avoid ISR nesting of the "Stepper Driver Interrupt". Should never occur though.
 static volatile uint8_t busy;   
 
@@ -189,8 +193,8 @@ void st_wake_up()
 
   if (sys.state & (STATE_CYCLE | STATE_HOMING)){
     // Initialize stepper output bits
-    st.dir_outbits = settings.dir_invert_mask; 
-    st.step_outbits = settings.step_invert_mask;
+    st.dir_outbits = dir_port_invert_mask; 
+    st.step_outbits = step_port_invert_mask;
     
     // Initialize step pulse timing from settings. Here to ensure updating after re-writing.
     #ifdef STEP_PULSE_DELAY
@@ -330,7 +334,7 @@ ISR(TIMER1_COMPA_vect)
         st.counter_z = st.counter_x;        
       }
 
-      st.dir_outbits = st.exec_block->direction_bits ^ settings.dir_invert_mask; 
+      st.dir_outbits = st.exec_block->direction_bits ^ dir_port_invert_mask; 
 
       #ifdef ADAPTIVE_MULTI_AXIS_STEP_SMOOTHING
         // With AMASS enabled, adjust Bresenham axis increment counters according to AMASS level.
@@ -399,7 +403,7 @@ ISR(TIMER1_COMPA_vect)
     if ( ++segment_buffer_tail == SEGMENT_BUFFER_SIZE) { segment_buffer_tail = 0; }
   }
 
-  st.step_outbits ^= settings.step_invert_mask;  // Apply step port invert mask    
+  st.step_outbits ^= step_port_invert_mask;  // Apply step port invert mask    
   busy = false;
 // SPINDLE_ENABLE_PORT ^= 1<<SPINDLE_ENABLE_BIT; // Debug: Used to time ISR
 }
@@ -419,7 +423,7 @@ ISR(TIMER1_COMPA_vect)
 ISR(TIMER0_OVF_vect)
 {
   // Reset stepping pins (leave the direction pins)
-  STEP_PORT = (STEP_PORT & ~STEP_MASK) | (settings.step_invert_mask & STEP_MASK); 
+  STEP_PORT = (STEP_PORT & ~STEP_MASK) | (step_port_invert_mask & STEP_MASK); 
   TCCR0B = 0; // Disable Timer0 to prevent re-entering this interrupt when it's not needed. 
 }
 #ifdef STEP_PULSE_DELAY
@@ -441,15 +445,28 @@ void st_reset()
   // Initialize stepper driver idle state.
   st_go_idle();
   
+  // Initialize stepper algorithm variables.
   memset(&prep, 0, sizeof(prep));
   memset(&st, 0, sizeof(st));
   st.exec_segment = NULL;
   pl_block = NULL;  // Planner block pointer used by segment buffer
-
   segment_buffer_tail = 0;
   segment_buffer_head = 0; // empty = tail
   segment_next_head = 1;
   busy = false;
+  
+  // Setup step and direction port invert masks.
+  uint8_t idx;
+  step_port_invert_mask = 0;
+  dir_port_invert_mask = 0;
+  for (idx=0; idx<N_AXIS; idx++) {
+    if (bit_istrue(settings.step_invert_mask,bit(idx))) { step_port_invert_mask |= get_step_pin_mask(idx); }
+    if (bit_istrue(settings.dir_invert_mask,bit(idx))) { dir_port_invert_mask |= get_direction_pin_mask(idx); }
+  }
+      
+  // Initialize step and direction port pins.
+  STEP_PORT = (STEP_PORT & ~STEP_MASK) | step_port_invert_mask;
+  DIRECTION_PORT = (DIRECTION_PORT & ~DIRECTION_MASK) | dir_port_invert_mask;
 }
 
 
@@ -458,10 +475,8 @@ void stepper_init()
 {
   // Configure step and direction interface pins
   STEP_DDR |= STEP_MASK;
-  STEP_PORT = (STEP_PORT & ~STEP_MASK) | settings.step_invert_mask;
   STEPPERS_DISABLE_DDR |= 1<<STEPPERS_DISABLE_BIT;
   DIRECTION_DDR |= DIRECTION_MASK;
-  DIRECTION_PORT = (DIRECTION_PORT & ~DIRECTION_MASK) | settings.dir_invert_mask;
 
   // Configure Timer 1: Stepper Driver Interrupt
   TCCR1B &= ~(1<<WGM13); // waveform generation = 0100 = CTC
@@ -815,9 +830,6 @@ void st_prep_buffer()
       }
     }
 
-// int32_t blength = segment_buffer_head - segment_buffer_tail;
-// if (blength < 0) { blength += SEGMENT_BUFFER_SIZE; } 
-// printInteger(blength);
   } 
 }      
 
@@ -827,13 +839,13 @@ void st_prep_buffer()
 // in the segment buffer. It will always be behind by up to the number of segment blocks (-1)
 // divided by the ACCELERATION TICKS PER SECOND in seconds. 
 #ifdef REPORT_REALTIME_RATE
-float st_get_realtime_rate()
-{
-   if (sys.state & (STATE_CYCLE | STATE_HOMING)){
-     return prep.current_speed;
-   }
-  return 0.0f;
-}
+  float st_get_realtime_rate()
+  {
+     if (sys.state & (STATE_CYCLE | STATE_HOMING | STATE_HOLD)){
+       return prep.current_speed;
+     }
+    return 0.0f;
+  }
 #endif
  
 /*