else if (rpm <= settings.rpm_min) {
        if (rpm == 0.0) { // S0 disables spindle
          sys.spindle_speed = 0.0;
          pwm_value = SPINDLE_PWM_OFF_VALUE;
        } else { // Set minimum PWM output
          sys.spindle_speed = settings.rpm_min;
          pwm_value = SPINDLE_PWM_MIN_VALUE;
        }

@@ -61,11 +61,12 @@ void spindle_stop()
   spindle_set_enable(false);
 	#ifdef SPINDLE_PWM_PIN
 		#ifndef INVERT_SPINDLE_PWM
 			grbl_analogWrite(SPINDLE_PWM_CHANNEL, SPINDLE_PWM_OFF_VALUE);
 		#else
-			grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION) - 1);
+//			grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION) - 1);
+			grbl_analogWrite(SPINDLE_PWM_CHANNEL, (1<<SPINDLE_PWM_BIT_PRECISION));
 		#endif
 	#endif
 }
 
 uint8_t spindle_get_state()  // returns SPINDLE_STATE_DISABLE, SPINDLE_STATE_CW or SPINDLE_STATE_CCW
@@ -138,15 +139,31 @@ uint32_t spindle_compute_pwm_value(float rpm)
 			pwm_value = SPINDLE_PWM_MIN_VALUE;
 			}
 		} else {
 			// Compute intermediate PWM value with linear spindle speed model.
 			// NOTE: A nonlinear model could be installed here, if required, but keep it VERY light-weight.
-			sys.spindle_speed = rpm;
-			pwm_value = floor((rpm-settings.rpm_min)*pwm_gradient) + SPINDLE_PWM_MIN_VALUE;
-		}		
-		
-		return(pwm_value);
+        #if (N_PIECES > 3)
+          if (rpm > RPM_POINT34) {
+            pwm_value = floor(RPM_LINE_A4*rpm - RPM_LINE_B4);
+          } else 
+        #endif
+        #if (N_PIECES > 2)
+          if (rpm > RPM_POINT23) {
+            pwm_value = floor(RPM_LINE_A3*rpm - RPM_LINE_B3);
+          } else 
+        #endif
+        #if (N_PIECES > 1)
+          if (rpm > RPM_POINT12) {
+            pwm_value = floor(RPM_LINE_A2*rpm - RPM_LINE_B2);
+          } else 
+        #endif
+        {
+          pwm_value = floor(RPM_LINE_A1*rpm - RPM_LINE_B1);
+        }
+      }
+   sys.spindle_speed = rpm;
+   return(pwm_value);
 	#else
 		return(0); // no SPINDLE_PWM_PIN
 	#endif
 }
 

@@ -126,12 +126,14 @@
 	// round down to nearest bit count for SPINDLE_PWM_MAX_VALUE = 13bits (8192)
 	
 	#define SPINDLE_PWM_BASE_FREQ 5000 // Hz
 	#define SPINDLE_PWM_BIT_PRECISION 8   
 	#define SPINDLE_PWM_OFF_VALUE     0
-	#define SPINDLE_PWM_MAX_VALUE     255
-	//#define INVERT_SPINDLE_PWM
+//	#define SPINDLE_PWM_MAX_VALUE     255
+#define INVERT_SPINDLE_PWM
+#define SPINDLE_PWM_MIN_VALUE 3
+#define SPINDLE_PWM_MAX_VALUE 195
 	
 	#ifndef SPINDLE_PWM_MIN_VALUE
 		#define SPINDLE_PWM_MIN_VALUE   1   // Must be greater than zero.
 	#endif

@@ -45,11 +45,12 @@ Some features should not be changed. See notes below.
 // Define CPU pin map and default settings.
 // NOTE: OEMs can avoid the need to maintain/update the defaults.h and cpu_map.h files and use only
 // one configuration file by placing their specific defaults and pin map at the bottom of this file.
 // If doing so, simply comment out these two defines and see instructions below.
 #define DEFAULTS_GENERIC
-#define CPU_MAP_TEST_DRIVE // these are defined in cpu_map.h
+//#define CPU_MAP_TEST_DRIVE // these are defined in cpu_map.h
+#define CPU_MAP_ESP32 // these are defined in cpu_map.h
 #define VERBOSE_HELP // adds addition help info, but could confuse some senders
 
 
 // Serial baud rate
 #define BAUD_RATE 115200
@@ -687,30 +688,27 @@ Some features should not be changed. See notes below.
 #define DISABLE_LASER_DURING_HOLD // Default enabled. Comment to disable.
 
 // Enables a piecewise linear model of the spindle PWM/speed output. Requires a solution by the
 // 'fit_nonlinear_spindle.py' script in the /doc/script folder of the repo. See file comments 
 // on how to gather spindle data and run the script to generate a solution.
-// #define ENABLE_PIECEWISE_LINEAR_SPINDLE  // Default disabled. Uncomment to enable.
+#define ENABLE_PIECEWISE_LINEAR_SPINDLE  // Default disabled. Uncomment to enable.
 
 // N_PIECES, RPM_MAX, RPM_MIN, RPM_POINTxx, and RPM_LINE_XX constants are all set and given by
 // the 'fit_nonlinear_spindle.py' script solution. Used only when ENABLE_PIECEWISE_LINEAR_SPINDLE
 // is enabled. Make sure the constant values are exactly the same as the script solution.
 // NOTE: When N_PIECES < 4, unused RPM_LINE and RPM_POINT defines are not required and omitted.
-#define N_PIECES 4  // Integer (1-4). Number of piecewise lines used in script solution.
-#define RPM_MAX  11686.4  // Max RPM of model. $30 > RPM_MAX will be limited to RPM_MAX.
-#define RPM_MIN  202.5    // Min RPM of model. $31 < RPM_MIN will be limited to RPM_MIN.
-#define RPM_POINT12  6145.4  // Used N_PIECES >=2. Junction point between lines 1 and 2.
-#define RPM_POINT23  9627.8  // Used N_PIECES >=3. Junction point between lines 2 and 3.
-#define RPM_POINT34  10813.9 // Used N_PIECES = 4. Junction point between lines 3 and 4.
-#define RPM_LINE_A1  3.197101e-03  // Used N_PIECES >=1. A and B constants of line 1.
-#define RPM_LINE_B1  -3.526076e-1
-#define RPM_LINE_A2  1.722950e-2   // Used N_PIECES >=2. A and B constants of line 2.
-#define RPM_LINE_B2  8.588176e+01
-#define RPM_LINE_A3  5.901518e-02  // Used N_PIECES >=3. A and B constants of line 3.
-#define RPM_LINE_B3  4.881851e+02
-#define RPM_LINE_A4  1.203413e-01  // Used N_PIECES = 4. A and B constants of line 4.
-#define RPM_LINE_B4  1.151360e+03
+#define N_PIECES 3
+#define RPM_MAX 23935.2
+#define RPM_MIN 2412.2
+#define RPM_POINT12 6283.9
+#define RPM_POINT23 11866.0
+#define RPM_LINE_A1 4.390865e-03
+#define RPM_LINE_B1 7.591787e+00
+#define RPM_LINE_A2 1.074874e-02
+#define RPM_LINE_B2 4.754411e+01
+#define RPM_LINE_A3 9.528342e-03
+#define RPM_LINE_B3 3.306286e+01
 
 
 /* ---------------------------------------------------------------------------------------
    OEM Single File Configuration Option