From 234195e721a58d4e46f21b63afcf1e5990570de0 Mon Sep 17 00:00:00 2001
From: Sungeun Jeon <chamnit@GneaAlpha.local>
Date: Fri, 27 Mar 2015 19:59:34 -0600
Subject: [PATCH] Compile-option for inverting spindle enable.

- Installed a compile-option for inverting the spindle enable pin for
certain electronics boards users have reported needing this.
---
 grbl/config.h          |  7 +++++++
 grbl/spindle_control.c | 24 ++++++++++++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/grbl/config.h b/grbl/config.h
index f430694..d45b260 100644
--- a/grbl/config.h
+++ b/grbl/config.h
@@ -156,6 +156,13 @@
 // NOTE: Will eventually be added to Grbl settings in v1.0.
 // #define INVERT_CONTROL_PIN // Default disabled. Uncomment to enable.
 
+// Inverts the spindle enable pin from low-disabled/high-enabled to low-enabled/high-disabled. Useful
+// for some pre-built electronic boards.
+// NOTE: If VARIABLE_SPINDLE is enabled(default), this option has no effect as the PWM output and 
+// spindle enable are combined to one pin. If you need both this option and spindle speed PWM, 
+// uncomment the config option USE_SPINDLE_DIR_AS_ENABLE_PIN below.
+// #define INVERT_SPINDLE_ENABLE_PIN // Default disabled. Uncomment to enable.
+
 // Enable limit pin states feedback in status reports. The data is presented as 0 (low) or 1(high), 
 // where the order is XYZ. For example, if the Y- and Z-limit pins are active, Grbl will include the 
 // following string in the status report "Lim:011". This is generally useful for setting up a new
diff --git a/grbl/spindle_control.c b/grbl/spindle_control.c
index 18c92ac..d9c5c10 100644
--- a/grbl/spindle_control.c
+++ b/grbl/spindle_control.c
@@ -49,10 +49,18 @@ void spindle_stop()
   #ifdef VARIABLE_SPINDLE
     TCCRA_REGISTER &= ~(1<<COMB_BIT); // Disable PWM. Output voltage is zero.
     #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN)
-      SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT); // Set pin to low.
+      #ifdef INVERT_SPINDLE_ENABLE_PIN
+		SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);  // Set pin to high
+	  #else
+		SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT); // Set pin to low
+	  #endif
     #endif
   #else
-    SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT); // Set pin to low.
+    #ifdef INVERT_SPINDLE_ENABLE_PIN
+	  SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);  // Set pin to high
+	#else
+	  SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT); // Set pin to low
+	#endif
   #endif  
 }
 
@@ -101,11 +109,19 @@ void spindle_set_state(uint8_t state, float rpm)
     
       // On the Uno, spindle enable and PWM are shared, unless otherwise specified.
       #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN) 
-        SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+        #ifdef INVERT_SPINDLE_ENABLE_PIN
+          SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+        #else
+          SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+        #endif
       #endif
       
     #else   
-      SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+      #ifdef INVERT_SPINDLE_ENABLE_PIN
+		SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+	  #else
+		SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+	  #endif
     #endif
 
   }