按源修正外部单位换算

结论：依据 LinuxCNC emccanon.cc 与 units.h，GET_EXTERNAL_LENGTH_UNITS 返回 user-units-per-mm 而非当前程序单位；新增 G20/G21 后 G92.3 恢复覆盖，native/source-link/test-native 均通过。

core/src/linuxcnc_canon_bridge.cpp

@@ -782,11 +782,16 @@ int GET_EXTERNAL_FLOOD() {
 }
 
 CANON_UNITS GET_EXTERNAL_LENGTH_UNIT_TYPE() {
-    return active_sink && active_sink->unit_scale() == 25.4 ? CANON_UNITS_INCHES : CANON_UNITS_MM;
+    // LinuxCNC src/emc/task/emccanon.cc derives this from INI machine/user
+    // units, not from the active G20/G21 program units.
+    return CANON_UNITS_MM;
 }
 
 double GET_EXTERNAL_LENGTH_UNITS() {
-    return active_sink ? active_sink->unit_scale() : 1.0;
+    // LinuxCNC src/emc/task/emccanon.cc returns traj.linearUnits here:
+    // external/user units per internal millimeter. The simulator has no INI
+    // machine-units bridge yet, so the source-linked default is metric.
+    return 1.0;
 }
 
 double GET_EXTERNAL_ANGLE_UNITS() {

test-linuxcnc-rs274-native.sh

@@ -1178,6 +1178,10 @@ CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs2
 # asserts that unit changes rescale current linear axes and work/G92 linear
 # offsets while rotary axes remain angular values.
 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_units_current_position.ngc >"$output_dir/cnc_sim_linuxcnc_units_current_position.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc convert_axis_offsets()
+# stores G92 offsets through PROGRAM_TO_USER_LEN and restores them through
+# USER_TO_PROGRAM_LEN after convert_length_units() changes active program units.
+CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_units_g92_restore.ngc >"$output_dir/cnc_sim_linuxcnc_units_g92_restore.json"
 CNC_SIM_RS274_NATIVE_OUTPUT_DIR="$output_dir" python3 - <<'PY'
 import json
 import os
@@ -1224,6 +1228,28 @@ if units_rapid[2]["start"] != units_rapid[2]["end"]:
 if (units_rapid[1]["end"]["a"], units_rapid[1]["end"]["b"], units_rapid[1]["end"]["c"]) != (4, 5, 6):
     raise SystemExit("LinuxCNC G21 unit change unexpectedly scaled rotary axes")
 
+units_g92_restore = load("cnc_sim_linuxcnc_units_g92_restore.json")
+units_g92_states = [
+    (
+        event["line"],
+        event["start"]["x"],
+        event["start"]["y"],
+        event["start"]["z"],
+        event["start"]["a"],
+        event["start"]["b"],
+        event["start"]["c"],
+    )
+    for event in units_g92_restore
+    if event["type"] == "set-g92-offset" and event["line"] > 0
+]
+expected_units_g92_states = [
+    (3, -1, -2, -3, -4, -5, -6),
+    (5, 0, 0, 0, 0, 0, 0),
+    (6, -25.4, -50.8, -76.2, -4, -5, -6),
+]
+if units_g92_states != expected_units_g92_states:
+    raise SystemExit(f"unexpected LinuxCNC G20/G21 G92 restore states: {units_g92_states!r}")
+
 fractional_linenumbers = load("cnc_sim_linuxcnc_fractional_linenumbers.json")
 fractional_spindle_states = [
     (event["line"], event["spindle"])
@@ -3076,6 +3102,7 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_good_imperial.jso
 echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_default.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_ini.err"
 echo "dumped $output_dir/cnc_sim_linuxcnc_units_current_position.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_units_g92_restore.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_predefined_positions.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_machine_coordinates.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_cutter_comp.json"

test-linuxcnc-source-link.sh

@@ -1864,6 +1864,12 @@ CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_units_current_position.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_units_current_position.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc convert_axis_offsets()
+# stores G92 offsets through PROGRAM_TO_USER_LEN and restores them through
+# USER_TO_PROGRAM_LEN after convert_length_units() changes active program units.
+CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_units_g92_restore.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_units_g92_restore.json"
 
 CNC_SIM_RS274_SOURCE_OUTPUT_DIR="$output_dir" python3 - <<'PY'
 import json
@@ -1922,6 +1928,28 @@ if units_rapid[2]["start"] != units_rapid[2]["end"]:
 if (units_rapid[1]["end"]["a"], units_rapid[1]["end"]["b"], units_rapid[1]["end"]["c"]) != (4, 5, 6):
     raise SystemExit("source-linked LinuxCNC G21 unit change unexpectedly scaled rotary axes")
 
+units_g92_restore = load("cnc_sim_linuxcnc_source_units_g92_restore.json")
+units_g92_states = [
+    (
+        event["line"],
+        event["start"]["x"],
+        event["start"]["y"],
+        event["start"]["z"],
+        event["start"]["a"],
+        event["start"]["b"],
+        event["start"]["c"],
+    )
+    for event in units_g92_restore
+    if event["type"] == "set-g92-offset" and event["line"] > 0
+]
+expected_units_g92_states = [
+    (3, -1, -2, -3, -4, -5, -6),
+    (5, 0, 0, 0, 0, 0, 0),
+    (6, -25.4, -50.8, -76.2, -4, -5, -6),
+]
+if units_g92_states != expected_units_g92_states:
+    raise SystemExit(f"unexpected source-linked LinuxCNC G20/G21 G92 restore states: {units_g92_states!r}")
+
 fractional_linenumbers = load("cnc_sim_linuxcnc_source_fractional_linenumbers.json")
 fractional_spindle_states = [
     (event["line"], event["spindle"])
@@ -4176,3 +4204,4 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_source_extended_linenumbers.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_close_and_downcase_words.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_percent_file_ignores_trailing.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_units_current_position.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_source_units_g92_restore.json"

tests/gcode/linuxcnc_units_g92_restore.ngc

@@ -0,0 +1,7 @@
+G20 G90 G17
+(Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc convert_length_units rescales G92 axis offsets, and convert_axis_offsets restores #5211-#5219 through USER_TO_PROGRAM_LEN and USER_TO_PROGRAM_ANG on G92.3.)
+G92 X1 Y2 Z3 A4 B5 C6
+G21
+G92.2
+G92.3
+M30