diff --git a/src/emc/motion/control.c b/src/emc/motion/control.c
index 8c9ce66..0ab0f5f 100644
--- a/src/emc/motion/control.c
+++ b/src/emc/motion/control.c
@@ -19,6 +19,9 @@
 #ifdef SWITCHKINS_DEBUG
 #include <stdio.h>  // rtpreempt only, consolidate to stderr
 #endif
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
 
 #include "posemath.h"
 #include "rtapi.h"
@@ -67,6 +70,46 @@ extern struct emcmot_status_t *emcmotStatus;
 //  etc.
 static double *pcmd_p[EMCMOT_MAX_AXIS];
 
+/* Optional simulation-only servo oracle.  It is disabled unless the caller
+ * provides a file path, so normal LinuxCNC motion timing is unchanged. */
+static FILE *xyzac_trace_stream;
+static void xyzac_trace_tick(void) {
+    const char *path;
+    int joint;
+    struct timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    if (xyzac_trace_stream == NULL) {
+        path = getenv("LINUXCNC_XYZAC_TRACE_FILE");
+        if (path == NULL || path[0] == '\0') return;
+        xyzac_trace_stream = fopen(path, "w");
+        if (xyzac_trace_stream == NULL) return;
+        setvbuf(xyzac_trace_stream, NULL, _IOLBF, 0);
+    }
+    fprintf(xyzac_trace_stream,
+            "{\"wall_ns\":%llu,\"motion_heartbeat\":%u,\"position\":[%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g],\"actual_position\":[%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g,%.17g],\"velocity\":%.17g,\"acceleration\":%.17g,\"queue_depth\":%d,\"active_depth\":%d,\"motion_id\":%d,\"motion_type\":%d,\"paused\":%d,\"queue_full\":%d,\"joints\":[",
+            (unsigned long long)now.tv_sec * 1000000000ull + (unsigned long long)now.tv_nsec,
+            emcmotStatus->heartbeat,
+            emcmotStatus->carte_pos_cmd.tran.x, emcmotStatus->carte_pos_cmd.tran.y, emcmotStatus->carte_pos_cmd.tran.z,
+            emcmotStatus->carte_pos_cmd.a, emcmotStatus->carte_pos_cmd.b, emcmotStatus->carte_pos_cmd.c,
+            emcmotStatus->carte_pos_cmd.u, emcmotStatus->carte_pos_cmd.v, emcmotStatus->carte_pos_cmd.w,
+            emcmotStatus->carte_pos_fb.tran.x, emcmotStatus->carte_pos_fb.tran.y, emcmotStatus->carte_pos_fb.tran.z,
+            emcmotStatus->carte_pos_fb.a, emcmotStatus->carte_pos_fb.b, emcmotStatus->carte_pos_fb.c,
+            emcmotStatus->carte_pos_fb.u, emcmotStatus->carte_pos_fb.v, emcmotStatus->carte_pos_fb.w,
+            emcmotStatus->current_vel, emcmotStatus->acc, emcmotStatus->depth,
+            emcmotStatus->activeDepth, emcmotStatus->id, emcmotStatus->motionType,
+            emcmotStatus->paused, emcmotStatus->queueFull);
+    for (joint = 0; joint < EMCMOT_MAX_JOINTS; ++joint) {
+        if (joint != 0) fputc(',', xyzac_trace_stream);
+        fprintf(xyzac_trace_stream, "{\"cmd\":%.17g,\"fb\":%.17g,\"vel\":%.17g,\"acc\":%.17g,\"homed\":%d}",
+                emcmotStatus->joint_status[joint].pos_cmd,
+                emcmotStatus->joint_status[joint].pos_fb,
+                emcmotStatus->joint_status[joint].vel_cmd,
+                emcmotStatus->joint_status[joint].acc_cmd,
+                emcmotStatus->joint_status[joint].homed);
+    }
+    fputs("]}\n", xyzac_trace_stream);
+}
+
 /***********************************************************************
 *                      LOCAL FUNCTION PROTOTYPES                       *
 ************************************************************************/
@@ -271,6 +314,7 @@ void emcmotController(void *arg, long period)
     update_status();
     /* here ends the core of the controller */
     emcmotStatus->heartbeat++;
+    xyzac_trace_tick();
     /* set tail to head, to indicate work complete */
     emcmotStatus->tail = emcmotStatus->head;
 /* end of controller function */