feedrate in °/min when moving only rotational axes

Marlin/src/module/planner.cpp

@@ -2083,6 +2083,10 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
 
  TERN_(LCD_SHOW_E_TOTAL, e_move_accumulator += steps_dist_mm.e);
 
+ #if HAS_ROTATIONAL_AXES
+ bool cartesian_move = true;
+ #endif
+
  if (true NUM_AXIS_GANG(
  && block->steps.a < MIN_STEPS_PER_SEGMENT,
  && block->steps.b < MIN_STEPS_PER_SEGMENT,
@@ -2101,8 +2105,8 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
  if (millimeters)
  block->millimeters = millimeters;
  else {
- /*
- *  Distance for interpretation of feedrate in accordance with LinuxCNC (the successor of NIST
+ /**
+ * Distance for interpretation of feedrate in accordance with LinuxCNC (the successor of NIST
  * RS274NGC interpreter - version 3)
  * Assume that X, Y, Z are the primary linear axes and U, V, W are secondary linear axes and A, B, C are
  * rotational axes. Then dX, dY, dZ are the displacements of the primary linear axes and dU, dV, dW are the displacements of linear axes and
@@ -2150,6 +2154,7 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
  #if HAS_ROTATIONAL_AXES
  if (NEAR_ZERO(distance_sqr)) {
  // Move involves only rotational axes. Calculate angular distance in accordance with LinuxCNC
+ cartesian_move = false;
  distance_sqr = ROTATIONAL_AXIS_GANG(sq(steps_dist_mm.i), + sq(steps_dist_mm.j), + sq(steps_dist_mm.k), + sq(steps_dist_mm.u), + sq(steps_dist_mm.v), + sq(steps_dist_mm.w));
  }
  #endif
@@ -2298,8 +2303,17 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
  const float inverse_millimeters = 1.0f / block->millimeters; // Inverse millimeters to remove multiple divides
 
  // Calculate inverse time for this move. No divide by zero due to previous checks.
- // Example: At 120mm/s a 60mm move takes 0.5s. So this will give 2.0.
- float inverse_secs = fr_mm_s * inverse_millimeters;
+ // Example: At 120mm/s a 60mm move involving XYZ axes takes 0.5s. So this will give 2.0.
+ // Example 2: At 120°/s a 60° move involving only rotational axes takes 0.5s. So this will give 2.0.
+ float inverse_secs;
+ #if HAS_ROTATIONAL_AXES
+ if (cartesian_move)
+ inverse_secs = fr_mm_s * inverse_millimeters;
+ else
+ inverse_secs = LINEAR_UNIT(fr_mm_s) * inverse_millimeters;
+ #else 
+ inverse_secs = fr_mm_s * inverse_millimeters;
+ #endif
 
  // Get the number of non busy movements in queue (non busy means that they can be altered)
  const uint8_t moves_queued = nonbusy_movesplanned();