feat(rs274ngc): MAX_UNWIND_TURNS auto rotary G0 rebase via G92

Add [AXIS_<L>] MAX_UNWIND_TURNS = N. On a G0 absolute move with the
rotary word, if the programmed (work-frame) delta exceeds N full turns,
fold the whole turns into the axis (G92) offset so the motor takes the
shortest path (within +/- 180 deg) to the target's angular position
while the work-frame position still reaches the commanded target. The
motion-side accumulated position is unchanged, so stepgens, encoders and
PID see no discontinuity.

Riding the existing G92 plumbing means the DRO, #<_a> and #5423 all
report the programmed value with no special-casing; the accumulated
turns appear as a G92 offset (#5214-#5216).

On re-home or estop reset the interpreter resynchronizes and detects the
frame re-anchor (a >180 deg work-frame jump on a managed axis with a
live offset); it collapses the stale offset back into the work frame and
re-emits the G92 so canon agrees, so a fresh home starts clean.

Gated to trivkins 1:1 axis-to-joint mapping; coupled kinematics (5-axis
TCP, gantry rotary) unsupported. Mutually exclusive with WRAPPED_ROTARY
(startup warning if both set on the same axis). Default 0 (disabled).

Author: grandixximo

docs/src/config/ini-config.adoc

@@ -1017,6 +1017,30 @@ The _<letter>_ specifies one of: X Y Z A B C U V W
   For a rotary axis (A,B,C typ) with unlimited rotation having no `MAX_LIMIT` for that axis in the `[AXIS_`<letter>`]` section a value of 1e99 is used.
 * `WRAPPED_ROTARY = 1` - (bool) When this is set to 1 for an ANGULAR axis the axis will move 0-359.999 degrees.
   Positive Numbers will move the axis in a positive direction and negative numbers will move the axis in the negative direction.
+* `MAX_UNWIND_TURNS = 10` - (real) When set to a positive value for a rotary axis (A, B, or C), enables automatic
+  unwind avoidance on G0 absolute moves. When a G0 with the rotary word would otherwise unwind more than
+  this many full turns from the current programmed position, the interpreter folds the whole turns into the
+  axis (G92) offset so the motor takes the shortest path (within +/- 180 degrees) to the target's angular
+  position while the programmed (work-frame) position still reaches the commanded target. Subsequent
+  G1/G0 absolute moves use the rebased frame. The motion-side traj.position remains accumulated, so
+  stepgens, encoders, and PID see no discontinuity.
++
+This is intended for rotational-cutting workflows (helical winding, spiral carving) where a G1 must
+honor literal multi-turn absolute targets but a terminal G0 should not unwind. CAM output and existing
+G-code do not need to change.
++
+Because the unwind rides the G92 offset, the DRO, `#5423`/`#5424`/`#5425` and `_a`/`_b`/`_c` named
+parameters all report the programmed value with no special handling, and the accumulated turns show up
+as a G92 offset (`#5214`/`#5215`/`#5216`). Consequences: the feature reserves G92 on a managed axis, so
+do not set G92 manually on an axis that has `MAX_UNWIND_TURNS` (use it freely on other axes); a `G92.1`
+in the program clears the accumulated unwind, after which the next qualifying G0 simply rebases again; and
+the offset is cleared automatically when the axis is re-homed or estop-reset, so a fresh home starts clean.
++
+The feature is gated to trivkins-style 1:1 axis-to-joint mapping; behavior in coupled kinematics
+(5-axis TCP, gantry rotary) is undefined and not supported. Mutually exclusive with `WRAPPED_ROTARY`;
+if both are set on the same axis, `MAX_UNWIND_TURNS` is ignored with a startup warning.
++
+Default: 0 (feature disabled).
 * `LOCKING_INDEXER_JOINT = 4` - (int) This value selects a joint to use for a locking indexer for the specified axis _<letter>_.
   In this example, the joint is 4 which would correspond to the B axis for a XYZAB system with trivkins (identity) kinematics.
   When set, a G0 move for this axis will initiate an unlock with the `joint.4.unlock pin` then wait for the `joint.4.is-unlocked` pin then move the joint at the rapid rate for that joint.

src/emc/rs274ngc/interp_convert.cc

@@ -5399,6 +5399,53 @@ int Interp::convert_straight(int move,   //!< either G_0 or G_1
   }
 
   settings->motion_mode = move;
+
+  // Auto-rotary-rebase: on a G0 with a rotary word, if the programmed
+  // (work-frame) delta exceeds MAX_UNWIND_TURNS, fold the whole turns of
+  // unwind into the axis (G92) offset so the motor takes the shortest path
+  // to the target's angular position (within +/- 180 deg) while the work-frame
+  // position still reaches the programmed target. Riding the existing G92
+  // plumbing means the DRO, #<_a> and #5423 all report the programmed value
+  // with no special-casing, and the motion-side accumulated position is left
+  // alone so stepgens, encoders and PID see no discontinuity.
+  // Only applies in absolute mode (G90); G53 explicitly bypasses; incremental
+  // (G91) does not need it.
+  if (move == G_0 &&
+      block->g_modes[GM_MODAL_0] != G_53 &&
+      settings->distance_mode == DISTANCE_MODE::ABSOLUTE) {
+      auto rebase = [](double cur, double *off, double max_turns, int flag,
+                       double bnum) -> bool {
+          if (!flag || max_turns <= 0.0) return false;
+          double delta = bnum - cur;
+          if (fabs(delta) / 360.0 <= max_turns) return false;
+          double mod = fmod(delta + 180.0, 360.0);
+          if (mod < 0.0) mod += 360.0;
+          double delta_short = mod - 180.0;
+          // Absorb the whole-turn remainder into the existing axis offset; the
+          // sub-turn delta_short is the only physical motion that results.
+          *off += (cur + delta_short) - bnum;
+          return true;
+      };
+      bool rebased = false;
+      rebased |= rebase(settings->AA_current, &settings->AA_axis_offset,
+                        settings->a_max_unwind_turns, block->a_flag, block->a_number);
+      rebased |= rebase(settings->BB_current, &settings->BB_axis_offset,
+                        settings->b_max_unwind_turns, block->b_flag, block->b_number);
+      rebased |= rebase(settings->CC_current, &settings->CC_axis_offset,
+                        settings->c_max_unwind_turns, block->c_flag, block->c_number);
+      if (rebased) {
+          SET_G92_OFFSET(settings->axis_offset_x, settings->axis_offset_y,
+                         settings->axis_offset_z, settings->AA_axis_offset,
+                         settings->BB_axis_offset, settings->CC_axis_offset,
+                         settings->u_axis_offset, settings->v_axis_offset,
+                         settings->w_axis_offset);
+          settings->parameters[G92_APPLIED] = 1.0;
+          settings->parameters[5214] = PROGRAM_TO_USER_ANG(settings->AA_axis_offset);
+          settings->parameters[5215] = PROGRAM_TO_USER_ANG(settings->BB_axis_offset);
+          settings->parameters[5216] = PROGRAM_TO_USER_ANG(settings->CC_axis_offset);
+      }
+  }
+
   CHP(find_ends(block, settings, &end_x, &end_y, &end_z,
                 &AA_end, &BB_end, &CC_end, &u_end, &v_end, &w_end));
 

src/emc/rs274ngc/interp_internal.hh

@@ -811,6 +811,15 @@ struct setup
   int b_axis_wrapped;
   int c_axis_wrapped;
 
+  // Per-axis automatic G0 unwind threshold, in turns.
+  // 0 disables; >0 makes a G0 that would otherwise unwind more than the
+  // threshold fold the whole turns into the axis (G92) offset, so the motor
+  // stays put while the work frame still reaches the programmed target.
+  // Mutually exclusive with WRAPPED_ROTARY.
+  double a_max_unwind_turns;
+  double b_max_unwind_turns;
+  double c_max_unwind_turns;
+
   int a_indexer_jnum;
   int b_indexer_jnum;
   int c_indexer_jnum;

src/emc/rs274ngc/rs274ngc_pre.cc

@@ -859,6 +859,9 @@ int Interp::init()
   _setup.a_axis_wrapped = 0;
   _setup.b_axis_wrapped = 0;
   _setup.c_axis_wrapped = 0;
+  _setup.a_max_unwind_turns = 0.0;
+  _setup.b_max_unwind_turns = 0.0;
+  _setup.c_max_unwind_turns = 0.0;
   _setup.random_toolchanger = 0;
   _setup.a_indexer_jnum = -1; // -1 means not used
   _setup.b_indexer_jnum = -1; // -1 means not used
@@ -888,6 +891,28 @@ int Interp::init()
           _setup.a_axis_wrapped = inifile.findBoolV("WRAPPED_ROTARY", "AXIS_A", false);
           _setup.b_axis_wrapped = inifile.findBoolV("WRAPPED_ROTARY", "AXIS_B", false);
           _setup.c_axis_wrapped = inifile.findBoolV("WRAPPED_ROTARY", "AXIS_C", false);
+
+          _setup.a_max_unwind_turns = inifile.findRealV("MAX_UNWIND_TURNS", "AXIS_A", 0.0);
+          _setup.b_max_unwind_turns = inifile.findRealV("MAX_UNWIND_TURNS", "AXIS_B", 0.0);
+          _setup.c_max_unwind_turns = inifile.findRealV("MAX_UNWIND_TURNS", "AXIS_C", 0.0);
+
+          struct UnwindCheck { const char *axis_name; int wrapped; double turns; };
+          UnwindCheck uw_checks[] = {
+              {"AXIS_A", _setup.a_axis_wrapped, _setup.a_max_unwind_turns},
+              {"AXIS_B", _setup.b_axis_wrapped, _setup.b_max_unwind_turns},
+              {"AXIS_C", _setup.c_axis_wrapped, _setup.c_max_unwind_turns},
+          };
+          for (auto &uw : uw_checks) {
+              if (uw.turns > 0.0 && uw.wrapped) {
+                  fprintf(stderr,
+                          "%s: MAX_UNWIND_TURNS is mutually exclusive with WRAPPED_ROTARY; "
+                          "MAX_UNWIND_TURNS ignored.\n", uw.axis_name);
+                  if (uw.axis_name[5] == 'A') _setup.a_max_unwind_turns = 0.0;
+                  if (uw.axis_name[5] == 'B') _setup.b_max_unwind_turns = 0.0;
+                  if (uw.axis_name[5] == 'C') _setup.c_max_unwind_turns = 0.0;
+              }
+          }
+
           _setup.random_toolchanger = inifile.findBoolV("RANDOM_TOOLCHANGER", "EMCIO", false);
           _setup.num_spindles = inifile.findIntV("SPINDLES", "TRAJ", 1);
 
@@ -2033,9 +2058,53 @@ int Interp::synch()
   _setup.control_mode = GET_EXTERNAL_MOTION_CONTROL_MODE();
   _setup.tolerance = GET_EXTERNAL_MOTION_CONTROL_TOLERANCE();
   _setup.naivecam_tolerance = GET_EXTERNAL_MOTION_CONTROL_NAIVECAM_TOLERANCE();
-  _setup.AA_current = GET_EXTERNAL_POSITION_A();
-  _setup.BB_current = GET_EXTERNAL_POSITION_B();
-  _setup.CC_current = GET_EXTERNAL_POSITION_C();
+  // Invalidate any MAX_UNWIND_TURNS auto-unwind G92 offset when the machine
+  // frame is re-anchored under us (homing, estop reset). Such an event snaps
+  // the external (work-frame) position by far more than any blend rounding
+  // while the interp was not commanding motion, so a jump over half a turn
+  // with a live offset on a managed axis means the accumulated frame is gone
+  // and the unwind offset is now stale. Collapse the offset back into the work
+  // frame and re-emit the G92 so canon agrees; otherwise the next absolute move
+  // would apply the stale offset and run onto the wrong path. A plain jog keeps
+  // machine and work frame moving together (sub-turn), so the offset stays
+  // valid and is left alone. Only managed axes (MAX_UNWIND_TURNS > 0) are
+  // touched, so a manually set G92 on an unmanaged axis is never disturbed.
+  {
+      double ext_a = GET_EXTERNAL_POSITION_A();
+      double ext_b = GET_EXTERNAL_POSITION_B();
+      double ext_c = GET_EXTERNAL_POSITION_C();
+      bool unwind_reset = false;
+      if (_setup.a_max_unwind_turns > 0.0 && _setup.AA_axis_offset != 0.0 &&
+          fabs(ext_a - _setup.AA_current) > 180.0) {
+          ext_a += _setup.AA_axis_offset;
+          _setup.AA_axis_offset = 0.0;
+          _setup.parameters[5214] = 0.0;
+          unwind_reset = true;
+      }
+      if (_setup.b_max_unwind_turns > 0.0 && _setup.BB_axis_offset != 0.0 &&
+          fabs(ext_b - _setup.BB_current) > 180.0) {
+          ext_b += _setup.BB_axis_offset;
+          _setup.BB_axis_offset = 0.0;
+          _setup.parameters[5215] = 0.0;
+          unwind_reset = true;
+      }
+      if (_setup.c_max_unwind_turns > 0.0 && _setup.CC_axis_offset != 0.0 &&
+          fabs(ext_c - _setup.CC_current) > 180.0) {
+          ext_c += _setup.CC_axis_offset;
+          _setup.CC_axis_offset = 0.0;
+          _setup.parameters[5216] = 0.0;
+          unwind_reset = true;
+      }
+      if (unwind_reset)
+          SET_G92_OFFSET(_setup.axis_offset_x, _setup.axis_offset_y,
+                         _setup.axis_offset_z, _setup.AA_axis_offset,
+                         _setup.BB_axis_offset, _setup.CC_axis_offset,
+                         _setup.u_axis_offset, _setup.v_axis_offset,
+                         _setup.w_axis_offset);
+      _setup.AA_current = ext_a;
+      _setup.BB_current = ext_b;
+      _setup.CC_current = ext_c;
+  }
   _setup.u_current  = GET_EXTERNAL_POSITION_U();
   _setup.v_current  = GET_EXTERNAL_POSITION_V();
   _setup.w_current  = GET_EXTERNAL_POSITION_W();