Add servo mode support for spindle PWM control

- Implemented USE_SPINDLE_SERVO_MODE configuration option
- Changed Timer2 prescaler from 1/8 to 1/1024 for ~50Hz servo frequency
- Added configurable servo pulse width range (SPINDLE_SERVO_MIN_PULSE/MAX_PULSE)
- M3 S0-S1000 now controls servo position (0-180 degrees)
- M5 positions servo to maximum position (pen up) instead of disabling PWM
- Default configuration supports pen plotter with reversed pulse values (MIN=31, MAX=16)
- Only supports ATmega328p (Arduino Uno) processors

Based on: https://www.buildlog.net/blog/2017/08/using-grbls-spindle-pwm-to-control-a-servo/

.gitignore

@@ -3,5 +3,6 @@
 *.elf
 *.DS_Store
 *.d
-
+.pio/
+.vscode/
 README.md

debug.md

@@ -0,0 +1,51 @@
+this is my curennt grbl state
+
+when homing the first limit switch encoutnered always retrun from homing. 
+it can be either the x or y
+how to fix
+```
+*** Connecting to jserialcomm://ttyUSB0:115200
+*** Fetching device status
+>>> ?
+<Alarm,MPos:0.000,0.000,0.000,WPos:1.002,-209.000,0.000>
+*** Fetching device version
+*** Fetching device settings
+>>> $$
+$0 = 10    (step pulse, usec)
+$1 = 25    (step idle delay, msec)
+$2 = 0    (step port invert mask:00000000)
+$3 = 2    (dir port invert mask:00000010)
+$4 = 0    (step enable invert, bool)
+$5 = 0    (limit pins invert, bool)
+$6 = 0    (probe pin invert, bool)
+$10 = 3    (status report mask:00000011)
+$11 = 0.010    (junction deviation, mm)
+$12 = 0.002    (arc tolerance, mm)
+$13 = 0    (report inches, bool)
+$20 = 1    (soft limits, bool)
+$21 = 0    (hard limits, bool)
+$22 = 1    (homing cycle, bool)
+$23 = 6    (homing dir invert mask:00000110)
+$24 = 25.000    (homing feed, mm/min)
+$25 = 500.000    (homing seek, mm/min)
+$26 = 250    (homing debounce, msec)
+$27 = 1.000    (homing pull-off, mm)
+$100 = 113.821    (x, step/mm)
+$101 = 100.000    (y, step/mm)
+$102 = 100.000    (z, step/mm)
+$110 = 8000.000    (x max rate, mm/min)
+$111 = 8000.000    (y max rate, mm/min)
+$112 = 8000.000    (z max rate, mm/min)
+$120 = 1200.000    (x accel, mm/sec^2)
+$121 = 1200.000    (y accel, mm/sec^2)
+$122 = 3800.000    (z accel, mm/sec^2)
+$130 = 310.000    (x max travel, mm)
+$131 = 210.000    (y max travel, mm)
+$132 = 100.000    (z max travel, mm)
+ok
+*** Fetching device state
+*** Connected to GRBL 0.9i
+>>> $G
+[G0 G54 G17 G21 G90 G94 M0 M5 M9 T0 F0. S0.]
+ok
+```

grbl/config.h

@@ -73,8 +73,10 @@
 // will not be affected by pin sharing.
 // NOTE: Defaults are set for a traditional 3-axis CNC machine. Z-axis first to clear, followed by X & Y.
 #define HOMING_CYCLE_0 (1<<Z_AXIS)                // REQUIRED: First move Z to clear workspace.
-#define HOMING_CYCLE_1 ((1<<X_AXIS)|(1<<Y_AXIS))  // OPTIONAL: Then move X,Y at the same time.
+// #define HOMING_CYCLE_1 ((1<<X_AXIS)|(1<<Y_AXIS))  // OPTIONAL: Then move X,Y at the same time.
 // #define HOMING_CYCLE_2                         // OPTIONAL: Uncomment and add axes mask to enable
+#define HOMING_CYCLE_0 (1<<X_AXIS)
+#define HOMING_CYCLE_1 (1<<Y_AXIS)
 
 // Number of homing cycles performed after when the machine initially jogs to limit switches.
 // This help in preventing overshoot and should improve repeatability. This value should be one or 
@@ -149,7 +151,7 @@
 // defined at (http://corexy.com/theory.html). Motors are assumed to positioned and wired exactly as
 // described, if not, motions may move in strange directions. Grbl requires the CoreXY A and B motors
 // have the same steps per mm internally.
-// #define COREXY // Default disabled. Uncomment to enable.
+#define COREXY // Default disabled. Uncomment to enable.
 
 // Inverts pin logic of the control command pins. This essentially means when this option is enabled
 // you can use normally-closed switches, rather than the default normally-open switches.
@@ -251,7 +253,7 @@
 // equally divided voltage bins between the maximum and minimum spindle speeds. So for a 5V pin, 1000
 // max rpm, and 250 min rpm, the spindle output voltage would be set for the following "S" commands: 
 // "S1000" @ 5V, "S250" @ 0.02V, and "S625" @ 2.5V (mid-range). The pin outputs 0V when disabled.
-#define SPINDLE_MAX_RPM 1000.0 // Max spindle RPM. This value is equal to 100% duty cycle on the PWM.
+#define SPINDLE_MAX_RPM 1200.0 // Max spindle RPM. This value is equal to 100% duty cycle on the PWM.
 #define SPINDLE_MIN_RPM 0.0    // Min spindle RPM. This value is equal to (1/256) duty cycle on the PWM.
 
 // Used by variable spindle output only. This forces the PWM output to a minimum duty cycle when enabled.
@@ -260,6 +262,23 @@
 // spindle RPM output lower than this value will be set to this value.
 // #define MINIMUM_SPINDLE_PWM 5 // Default disabled. Uncomment to enable. Integer (0-255)
 
+// Enable servo mode for spindle PWM output. This changes the PWM frequency from ~1kHz to ~50Hz
+// and adjusts the duty cycle range to control hobby servos (1-2ms pulses). When enabled, the
+// spindle RPM values are mapped to servo positions (S0-S180 or configured min/max).
+// This is useful for pen plotters, drag knives, or other applications requiring servo control.
+// Based on: https://www.buildlog.net/blog/2017/08/using-grbls-spindle-pwm-to-control-a-servo/
+// NOTE: Only works with VARIABLE_SPINDLE enabled and ATmega328p (Uno) processors.
+// NOTE: This changes Timer2 prescaler from 1/8 to 1/1024, resulting in ~61Hz PWM frequency.
+// NOTE: Connect servo signal wire to Arduino Pin D11 (same as spindle PWM output).
+//       Servo power (5V) and ground must be connected to appropriate power source.
+#define USE_SPINDLE_SERVO_MODE // Default disabled. Uncomment to enable.
+
+// Servo pulse width range (in timer ticks). Only used with USE_SPINDLE_SERVO_MODE enabled.
+// At 1/1024 prescaler on 16MHz, each tick = 64μs. Default values: 16 ticks = 1.024ms, 31 ticks = 1.984ms
+// Adjust these if your servo requires different pulse widths for 0° and 180° positions.
+#define SPINDLE_SERVO_MIN_PULSE 31  // Servo position at minimum RPM (S0) - pen DOWN - ~2ms pulse
+#define SPINDLE_SERVO_MAX_PULSE 16  // Servo position at maximum RPM (S1000/M5) - pen UP - ~1ms pulse
+
 // By default on a 328p(Uno), Grbl combines the variable spindle PWM and the enable into one pin to help
 // preserve I/O pins. For certain setups, these may need to be separate pins. This configure option uses
 // the spindle direction pin(D13) as a separate spindle enable pin along with spindle speed PWM on pin D11.
@@ -407,6 +426,18 @@
   #error "USE_SPINDLE_DIR_AS_ENABLE_PIN may only be used with a 328p processor"
 #endif
 
+#if defined(USE_SPINDLE_SERVO_MODE) && !defined(VARIABLE_SPINDLE)
+  #error "USE_SPINDLE_SERVO_MODE may only be used with VARIABLE_SPINDLE enabled"
+#endif
+
+#if defined(USE_SPINDLE_SERVO_MODE) && !defined(CPU_MAP_ATMEGA328P)
+  #error "USE_SPINDLE_SERVO_MODE may only be used with a 328p processor"
+#endif
+
+#if defined(USE_SPINDLE_SERVO_MODE) && (SPINDLE_SERVO_MIN_PULSE == SPINDLE_SERVO_MAX_PULSE)
+  #error "SPINDLE_SERVO_MIN_PULSE and SPINDLE_SERVO_MAX_PULSE cannot be equal"
+#endif
+
 // ---------------------------------------------------------------------------------------
 
 

grbl/spindle_control.c

@@ -45,22 +45,38 @@ void spindle_init()
 
 void spindle_stop()
 {
-  // On the Uno, spindle enable and PWM are shared. Other CPUs have seperate enable pin.
+  #ifdef USE_SPINDLE_SERVO_MODE
-  #ifdef VARIABLE_SPINDLE
+    // Servo mode: M5 moves servo to maximum position (e.g., pen up) instead of disabling PWM
-    TCCRA_REGISTER &= ~(1<<COMB_BIT); // Disable PWM. Output voltage is zero.
+    // This keeps the servo powered and in position
+    TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
+    TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x07; // 1/1024 prescaler
+    OCR_REGISTER = SPINDLE_SERVO_MAX_PULSE; // Set to maximum position
+    
     #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN)
+      #ifdef INVERT_SPINDLE_ENABLE_PIN
+        SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+      #else
+        SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+      #endif
+    #endif
+  #else
+    // Standard spindle mode: Disable PWM output
+    #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)
+        #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
       #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
-    #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
 }
 
@@ -83,7 +99,6 @@ void spindle_set_state(uint8_t state, float rpm)
     #endif
 
     #ifdef VARIABLE_SPINDLE
-      // TODO: Install the optional capability for frequency-based output for servos.
       #ifdef CPU_MAP_ATMEGA2560
       	TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
         TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02 | (1<<WAVE2_REGISTER) | (1<<WAVE3_REGISTER); // set to 1/8 Prescaler
@@ -91,33 +106,69 @@ void spindle_set_state(uint8_t state, float rpm)
         uint16_t current_pwm;
       #else
         TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
-        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // set to 1/8 Prescaler
+        #ifdef USE_SPINDLE_SERVO_MODE
+          // Servo mode: Set to 1/1024 prescaler for ~50Hz frequency (actually ~61Hz on 16MHz)
+          // Timer formula: Freq = F_CPU / (Prescaler * 256) = 16MHz / (1024 * 256) = 61.04Hz
+          // This provides the ~20ms period needed for servo control (50Hz ideal, 61Hz acceptable)
+          TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x07; // CS22=1, CS21=1, CS20=1 = 1/1024 prescaler
+        #else
+          // Standard spindle mode: Set to 1/8 prescaler for ~7.8kHz frequency
+          TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // CS21=1 = 1/8 prescaler
+        #endif
         uint8_t current_pwm;
       #endif
 
-      if (rpm <= 0.0) { spindle_stop(); } // RPM should never be negative, but check anyway.
+      #ifdef USE_SPINDLE_SERVO_MODE
-      else {
+        // Servo mode: Allow rpm=0 as valid position (0 degrees), only stop on negative
-        #define SPINDLE_RPM_RANGE (SPINDLE_MAX_RPM-SPINDLE_MIN_RPM)
+        if (rpm < 0.0) { spindle_stop(); }
-        if ( rpm < SPINDLE_MIN_RPM ) { rpm = 0; } 
         else {
+          // Servo mode: Map RPM range to servo pulse width (16-31 ticks = ~1-2ms pulses)
+          // Each tick at 1/1024 prescaler = 64μs, so 16 ticks ≈ 1.024ms, 31 ticks ≈ 1.984ms
+          #define SPINDLE_SERVO_RANGE (SPINDLE_SERVO_MAX_PULSE - SPINDLE_SERVO_MIN_PULSE)
+          #define SPINDLE_RPM_RANGE (SPINDLE_MAX_RPM-SPINDLE_MIN_RPM)
+          if ( rpm < SPINDLE_MIN_RPM ) { rpm = SPINDLE_MIN_RPM; }
+          if ( rpm > SPINDLE_MAX_RPM ) { rpm = SPINDLE_MAX_RPM; }
           rpm -= SPINDLE_MIN_RPM;
-          if ( rpm > SPINDLE_RPM_RANGE ) { rpm = SPINDLE_RPM_RANGE; } // Prevent integer overflow
+          // Map RPM to servo pulse range
-        }
+          current_pwm = floor( rpm * (SPINDLE_SERVO_RANGE / SPINDLE_RPM_RANGE) + SPINDLE_SERVO_MIN_PULSE + 0.5);
-        current_pwm = floor( rpm*(PWM_MAX_VALUE/SPINDLE_RPM_RANGE) + 0.5);
+          OCR_REGISTER = current_pwm; // Set PWM pin output
-        #ifdef MINIMUM_SPINDLE_PWM
-          if (current_pwm < MINIMUM_SPINDLE_PWM) { current_pwm = MINIMUM_SPINDLE_PWM; }
-        #endif
-        OCR_REGISTER = current_pwm; // Set PWM pin output
     
-        // On the Uno, spindle enable and PWM are shared, unless otherwise specified.
+          // On the Uno, spindle enable and PWM are shared, unless otherwise specified.
-        #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN) 
+          #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN)
-          #ifdef INVERT_SPINDLE_ENABLE_PIN
+            #ifdef INVERT_SPINDLE_ENABLE_PIN
-            SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+              SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
-          #else
+            #else
-            SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+              SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+            #endif
           #endif
-        #endif
+        }
-      }
+      #else
+        // Standard spindle mode: Stop on zero or negative RPM
+        if (rpm <= 0.0) { spindle_stop(); }
+        else {
+          // Standard spindle mode: Map RPM range to full PWM range (0-255)
+          #define SPINDLE_RPM_RANGE (SPINDLE_MAX_RPM-SPINDLE_MIN_RPM)
+          if ( rpm < SPINDLE_MIN_RPM ) { rpm = 0; }
+          else {
+            rpm -= SPINDLE_MIN_RPM;
+            if ( rpm > SPINDLE_RPM_RANGE ) { rpm = SPINDLE_RPM_RANGE; } // Prevent integer overflow
+          }
+          current_pwm = floor( rpm*(PWM_MAX_VALUE/SPINDLE_RPM_RANGE) + 0.5);
+          #ifdef MINIMUM_SPINDLE_PWM
+            if (current_pwm < MINIMUM_SPINDLE_PWM) { current_pwm = MINIMUM_SPINDLE_PWM; }
+          #endif
+          OCR_REGISTER = current_pwm; // Set PWM pin output
+    
+          // On the Uno, spindle enable and PWM are shared, unless otherwise specified.
+          #if defined(CPU_MAP_ATMEGA2560) || defined(USE_SPINDLE_DIR_AS_ENABLE_PIN)
+            #ifdef INVERT_SPINDLE_ENABLE_PIN
+              SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
+            #else
+              SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
+            #endif
+          #endif
+        }
+      #endif
       
     #else
       // NOTE: Without variable spindle, the enable bit should just turn on or off, regardless

platformio.ini

@@ -0,0 +1,41 @@
+; PlatformIO Project Configuration File for Grbl
+;
+; This configuration builds Grbl v0.9j for Arduino Uno (ATmega328P)
+; Based on the original Makefile settings
+;
+; Please visit documentation for options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[platformio]
+src_dir = src
+lib_dir = .
+include_dir = grbl
+
+[env:uno]
+platform = atmelavr
+board = uno
+framework = arduino
+
+; Build configuration matching Makefile
+build_flags =
+    -DF_CPU=16000000L
+    -DBAUD_RATE=115200
+    -Wall
+    -Os
+    -ffunction-sections
+    -fdata-sections
+    -Wl,--gc-sections
+    -lm
+    -Igrbl
+    -Igrbl/cpu_map
+    -Igrbl/defaults
+
+; Add Grbl source files to build
+build_src_filter =
+    +<*>
+    +<../grbl/*.c>
+    -<../grbl/examples/>
+
+; Upload configuration
+upload_speed = 115200
+monitor_speed = 115200