Planner trapezoidal nominal_rate fix

Marlin/src/HAL/ESP32/timers.h

@@ -53,12 +53,11 @@ typedef uint64_t hal_timer_t;
 #if ENABLED(I2S_STEPPER_STREAM)
   #define STEPPER_TIMER_PRESCALE     1
   #define STEPPER_TIMER_RATE         250000                           // 250khz, 4µs pulses of i2s word clock
-  #define STEPPER_TIMER_TICKS_PER_US ((STEPPER_TIMER_RATE) / 1000000) // stepper timer ticks per µs // wrong would be 0.25
 #else
   #define STEPPER_TIMER_PRESCALE     40
   #define STEPPER_TIMER_RATE         ((HAL_TIMER_RATE) / (STEPPER_TIMER_PRESCALE)) // frequency of stepper timer, 2MHz
-  #define STEPPER_TIMER_TICKS_PER_US ((STEPPER_TIMER_RATE) / 1000000)              // stepper timer ticks per µs
 #endif
+#define STEPPER_TIMER_TICKS_PER_US   ((STEPPER_TIMER_RATE) / 1000000) // stepper timer ticks per µs
 
 #define STEP_TIMER_MIN_INTERVAL   8 // minimum time in µs between stepper interrupts
 

Marlin/src/HAL/TEENSY31_32/timers.h

@@ -41,7 +41,7 @@ typedef uint32_t hal_timer_t;
 #define FTM0_TIMER_PRESCALE_BITS 0b011
 #define FTM1_TIMER_PRESCALE_BITS 0b010
 
-#define FTM0_TIMER_RATE (F_BUS / (FTM0_TIMER_PRESCALE)) // 60MHz / 8 = 7500kHz
+#define FTM0_TIMER_RATE (F_BUS / (FTM0_TIMER_PRESCALE)) // 60MHz / 8 = 7.5MHz
 #define FTM1_TIMER_RATE (F_BUS / (FTM1_TIMER_PRESCALE)) // 60MHz / 4 = 15MHz
 
 #define HAL_TIMER_RATE         (FTM0_TIMER_RATE)

Marlin/src/module/planner.cpp

@@ -730,8 +730,6 @@ void Planner::init() {
   #endif
 #endif
 
-#define MINIMAL_STEP_RATE 120
-
 /**
  * Get the current block for processing
  * and mark the block as busy.
@@ -799,14 +797,14 @@ void Planner::calculate_trapezoid_for_block(block_t * const block, const_float_t
   uint32_t initial_rate = LROUND(block->nominal_rate * entry_factor),
            final_rate = LROUND(block->nominal_rate * exit_factor); // (steps per second)
 
-  // Legacy check against supposed timer overflow. However Stepper::calc_timer_interval() already
-  // should protect against it. But removing this code produces judder in direction-switching
-  // moves. This is because the current discrete stepping math diverges from physical motion under
-  // constant acceleration when acceleration_steps_per_s2 is large compared to initial/final_rate.
+  // Limit minimal step rate (Otherwise the timer will overflow.)
   NOLESS(initial_rate, uint32_t(MINIMAL_STEP_RATE));  // Enforce the minimum speed
   NOLESS(final_rate, uint32_t(MINIMAL_STEP_RATE));
-  NOMORE(initial_rate, block->nominal_rate);          // NOTE: The nominal rate may be less than MINIMAL_STEP_RATE!
-  NOMORE(final_rate, block->nominal_rate);
+  NOLESS(block->nominal_rate, MINIMAL_STEP_RATE);
+
+  // Assume these are handled elsewhere. Retained for debugging.
+  //NOMORE(initial_rate, block->nominal_rate);        // NOTE: The nominal rate may be less than MINIMAL_STEP_RATE!
+  //NOMORE(final_rate, block->nominal_rate);
 
   #if ANY(S_CURVE_ACCELERATION, LIN_ADVANCE)
     // If we have some plateau time, the cruise rate will be the nominal rate

Marlin/src/module/planner.h

@@ -78,6 +78,14 @@
   #include "../feature/closedloop.h"
 #endif
 
+constexpr uint32_t MINIMAL_STEP_RATE = (
+  #ifdef CPU_32_BIT
+    _MAX((STEPPER_TIMER_RATE) / HAL_TIMER_TYPE_MAX, 1U) // 32-bit shouldn't go below 1
+  #else
+    (F_CPU) / 500000U   // AVR shouldn't go below 32 (16MHz) or 40 (20MHz)
+  #endif
+);
+
 // Feedrate for manual moves
 #ifdef MANUAL_FEEDRATE
   constexpr xyze_feedrate_t manual_feedrate_mm_m = MANUAL_FEEDRATE,

Marlin/src/module/stepper.cpp

@@ -2173,15 +2173,15 @@ void Stepper::pulse_phase_isr() {
 // Calculate timer interval, with all limits applied.
 hal_timer_t Stepper::calc_timer_interval(uint32_t step_rate) {
 
+  constexpr uint32_t min_step_rate = MINIMAL_STEP_RATE;
+
   #ifdef CPU_32_BIT
 
     // A fast processor can just do integer division
-    constexpr uint32_t min_step_rate = uint32_t(STEPPER_TIMER_RATE) / HAL_TIMER_TYPE_MAX;
     return step_rate > min_step_rate ? uint32_t(STEPPER_TIMER_RATE) / step_rate : HAL_TIMER_TYPE_MAX;
 
   #else
 
-    constexpr uint32_t min_step_rate = (F_CPU) / 500000U; // i.e., 32 or 40
     if (step_rate >= 0x0800) {  // higher step rate
       // AVR is able to keep up at around 65kHz Stepping ISR rate at most.
       // So values for step_rate > 65535 might as well be truncated.