First draft of Unified Stepper / E Advance ISR

Marlin/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/Cartesio/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/Felix/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/Hephestos/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/K8200/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/K8400/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/RigidBot/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/SCARA/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/TAZ4/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/WITBOX/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/delta/biv2.5/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/delta/generic/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/makibox/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

  *
  * Assumption: advance = k * (delta velocity)
  * K=0 means advance disabled.
- * To get a rough start value for calibration, measure your "free filament length"
- * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
- * your setup, where L is the "free filament length":
- *
- * Filament diameter           |   1.75mm  |    3.0mm   |
- * ----------------------------|-----------|------------|
- * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
- * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * See Marlin documentation for calibration instructions.
  */
 //#define LIN_ADVANCE
 

Marlin/stepper.cpp

 
 #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
 
-  uint8_t Stepper::old_OCR0A = 0;
-  volatile uint8_t Stepper::eISR_Rate = 200; // Keep the ISR at a low rate until needed
+  uint16_t Stepper::nextMainISR = 0,
+           Stepper::nextAdvanceISR = 65535,
+           Stepper::eISR_Rate = 65535;
 
   #if ENABLED(LIN_ADVANCE)
     volatile int Stepper::e_steps[E_STEPPERS];
  *  2000     1 KHz - sleep rate
  *  4000   500  Hz - init rate
  */
-ISR(TIMER1_COMPA_vect) { Stepper::isr(); }
+ISR(TIMER1_COMPA_vect) {
+  #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
+    Stepper::advance_isr_scheduler();
+  #else
+    Stepper::isr();
+  #endif
+}
 
 void Stepper::isr() {
-  //Disable Timer0 ISRs and enable global ISR again to capture UART events (incoming chars)
-  #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-    CBI(TIMSK0, OCIE0A); //estepper ISR
+  #define _ENABLE_ISRs() cli(); SBI(TIMSK0, OCIE0B); ENABLE_STEPPER_DRIVER_INTERRUPT()
+
+  #if DISABLED(ADVANCE) && DISABLED(LIN_ADVANCE)
+    //Disable Timer0 ISRs and enable global ISR again to capture UART events (incoming chars)
+    CBI(TIMSK0, OCIE0B); //Temperature ISR
+    DISABLE_STEPPER_DRIVER_INTERRUPT();
+    sei();
   #endif
-  CBI(TIMSK0, OCIE0B); //Temperature ISR
-  DISABLE_STEPPER_DRIVER_INTERRUPT();
-  sei();
 
   if (cleaning_buffer_counter) {
     --cleaning_buffer_counter;
     #ifdef SD_FINISHED_RELEASECOMMAND
       if (!cleaning_buffer_counter && (SD_FINISHED_STEPPERRELEASE)) enqueue_and_echo_commands_P(PSTR(SD_FINISHED_RELEASECOMMAND));
     #endif
-    OCR1A = 200; // Run at max speed - 10 KHz
-    //re-enable ISRs
-    #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-      SBI(TIMSK0, OCIE0A);
-    #endif
-    SBI(TIMSK0, OCIE0B);
-    ENABLE_STEPPER_DRIVER_INTERRUPT();
+    _NEXT_ISR(200); // Run at max speed - 10 KHz
+    _ENABLE_ISRs(); // re-enable ISRs
     return;
   }
 
       #if ENABLED(Z_LATE_ENABLE)
         if (current_block->steps[Z_AXIS] > 0) {
           enable_z();
-          OCR1A = 2000; // Run at slow speed - 1 KHz
-          #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-            SBI(TIMSK0, OCIE0A);
-          #endif
-          SBI(TIMSK0, OCIE0B);
-          ENABLE_STEPPER_DRIVER_INTERRUPT();
+          _NEXT_ISR(2000); // Run at slow speed - 1 KHz
+          _ENABLE_ISRs(); // re-enable ISRs
           return;
         }
       #endif
       // #endif
     }
     else {
-      OCR1A = 2000; // Run at slow speed - 1 KHz
-      #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-        SBI(TIMSK0, OCIE0A);
-      #endif
-      SBI(TIMSK0, OCIE0B);
-      ENABLE_STEPPER_DRIVER_INTERRUPT();
+      _NEXT_ISR(2000); // Run at slow speed - 1 KHz
+      _ENABLE_ISRs(); // re-enable ISRs
       return;
     }
   }
 
   #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
     // If we have esteps to execute, fire the next advance_isr "now"
-    if (e_steps[TOOL_E_INDEX]) OCR0A = TCNT0 + 2;
+    if (e_steps[TOOL_E_INDEX]) nextAdvanceISR = 0;
   #endif
 
   // Calculate new timer value
 
     // step_rate to timer interval
     uint16_t timer = calc_timer(acc_step_rate);
-    OCR1A = timer;
+    _NEXT_ISR(timer);
     acceleration_time += timer;
 
     #if ENABLED(LIN_ADVANCE)
     #endif // ADVANCE or LIN_ADVANCE
 
     #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-      eISR_Rate = (timer >> 3) * step_loops / abs(e_steps[TOOL_E_INDEX]); //>> 3 is divide by 8. Reason: Timer 1 runs at 16/8=2MHz, Timer 0 at 16/64=0.25MHz. ==> 2/0.25=8.
+      eISR_Rate = !e_steps[TOOL_E_INDEX] ? 65535 : timer * step_loops / abs(e_steps[TOOL_E_INDEX]);
     #endif
   }
   else if (step_events_completed > (uint32_t)current_block->decelerate_after) {
 
     // step_rate to timer interval
     uint16_t timer = calc_timer(step_rate);
-    OCR1A = timer;
+    _NEXT_ISR(timer);
     deceleration_time += timer;
 
     #if ENABLED(LIN_ADVANCE)
     #endif // ADVANCE or LIN_ADVANCE
 
     #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-      eISR_Rate = (timer >> 3) * step_loops / abs(e_steps[TOOL_E_INDEX]);
+      eISR_Rate = !e_steps[TOOL_E_INDEX] ? 65535 : timer * step_loops / abs(e_steps[TOOL_E_INDEX]);
     #endif
   }
   else {
       if (current_block->use_advance_lead)
         current_estep_rate[TOOL_E_INDEX] = final_estep_rate;
 
-      eISR_Rate = (OCR1A_nominal >> 3) * step_loops_nominal / abs(e_steps[TOOL_E_INDEX]);
+      eISR_Rate = !e_steps[TOOL_E_INDEX] ? 65535 : OCR1A_nominal * step_loops_nominal / abs(e_steps[TOOL_E_INDEX]);
 
     #endif
 
-    OCR1A = OCR1A_nominal;
+    _NEXT_ISR(OCR1A_nominal);
     // ensure we're running at the correct step rate, even if we just came off an acceleration
     step_loops = step_loops_nominal;
   }
 
-  NOLESS(OCR1A, TCNT1 + 16);
+  #if DISABLED(ADVANCE) && DISABLED(LIN_ADVANCE)
+    NOLESS(OCR1A, TCNT1 + 16);
+  #endif
 
   // If current block is finished, reset pointer
   if (all_steps_done) {
     current_block = NULL;
     planner.discard_current_block();
   }
-  #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-    SBI(TIMSK0, OCIE0A);
+  #if DISABLED(ADVANCE) && DISABLED(LIN_ADVANCE)
+    _ENABLE_ISRs(); // re-enable ISRs
   #endif
-  SBI(TIMSK0, OCIE0B);
-  ENABLE_STEPPER_DRIVER_INTERRUPT();
 }
 
 #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
 
   // Timer interrupt for E. e_steps is set in the main routine;
-  // Timer 0 is shared with millies
-  ISR(TIMER0_COMPA_vect) { Stepper::advance_isr(); }
 
   void Stepper::advance_isr() {
-
-    old_OCR0A += eISR_Rate;
-    OCR0A = old_OCR0A;
-
+    
+    nextAdvanceISR = eISR_Rate;
+    
     #define SET_E_STEP_DIR(INDEX) \
       if (e_steps[INDEX]) E## INDEX ##_DIR_WRITE(e_steps[INDEX] < 0 ? INVERT_E## INDEX ##_DIR : !INVERT_E## INDEX ##_DIR)
 
 
   }
 
+  void Stepper::advance_isr_scheduler() {
+    // Disable Timer0 ISRs and enable global ISR again to capture UART events (incoming chars)
+    CBI(TIMSK0, OCIE0B); // Temperature ISR
+    DISABLE_STEPPER_DRIVER_INTERRUPT();
+    sei();
+
+    // Run main stepping ISR if flagged
+    if (!nextMainISR) isr();
+
+    // Run Advance stepping ISR if flagged
+    if (!nextAdvanceISR) advance_isr();
+  
+    // Is the next advance ISR scheduled before the next main ISR?
+    if (nextAdvanceISR <= nextMainISR) {
+      // Set up the next interrupt
+      OCR1A = nextAdvanceISR;
+      // New interval for the next main ISR
+      if (nextMainISR) nextMainISR -= nextAdvanceISR;
+      // Will call Stepper::advance_isr on the next interrupt
+      nextAdvanceISR = 0;
+    }
+    else {
+      // The next main ISR comes first
+      OCR1A = nextMainISR;
+      // New interval for the next advance ISR, if any
+      if (nextAdvanceISR && nextAdvanceISR != 65535)
+        nextAdvanceISR -= nextMainISR;
+      // Will call Stepper::isr on the next interrupt
+      nextMainISR = 0;
+    }
+  
+    // Don't run the ISR faster than possible
+    NOLESS(OCR1A, TCNT1 + 16);
+
+    // Restore original ISR settings
+    cli();
+    SBI(TIMSK0, OCIE0B);
+    ENABLE_STEPPER_DRIVER_INTERRUPT();
+  }
+
 #endif // ADVANCE or LIN_ADVANCE
 
 void Stepper::init() {
       #endif
     }
 
-    #if defined(TCCR0A) && defined(WGM01)
-      CBI(TCCR0A, WGM01);
-      CBI(TCCR0A, WGM00);
-    #endif
-    SBI(TIMSK0, OCIE0A);
-
   #endif // ADVANCE or LIN_ADVANCE
 
   endstops.enable(true); // Start with endstops active. After homing they can be disabled

Marlin/stepper.h

     static volatile uint32_t step_events_completed; // The number of step events executed in the current block
 
     #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
-      static uint8_t old_OCR0A;
-      static volatile uint8_t eISR_Rate;
+      static uint16_t nextMainISR, nextAdvanceISR, eISR_Rate;
+      #define _NEXT_ISR(T) nextMainISR = T
       #if ENABLED(LIN_ADVANCE)
         static volatile int e_steps[E_STEPPERS];
         static int final_estep_rate;
         static long advance_rate, advance, final_advance;
         static long old_advance;
       #endif
+    #else
+      #define _NEXT_ISR(T) OCR1A = T
     #endif // ADVANCE or LIN_ADVANCE
 
     static long acceleration_time, deceleration_time;
 
     #if ENABLED(ADVANCE) || ENABLED(LIN_ADVANCE)
       static void advance_isr();
+      static void advance_isr_scheduler();
     #endif
 
     //
       return timer;
     }
 
-    // Initializes the trapezoid generator from the current block. Called whenever a new
-    // block begins.
+    // Initialize the trapezoid generator from the current block.
+    // Called whenever a new block begins.
     static FORCE_INLINE void trapezoid_generator_reset() {
 
       static int8_t last_extruder = -1;
       step_loops_nominal = step_loops;
       acc_step_rate = current_block->initial_rate;
       acceleration_time = calc_timer(acc_step_rate);
-      OCR1A = acceleration_time;
+      _NEXT_ISR(acceleration_time);
 
       #if ENABLED(LIN_ADVANCE)
         if (current_block->use_advance_lead) {