Index: plugins/rt_topo/crbs_route.c
===================================================================
--- plugins/rt_topo/crbs_route.c	(revision 1447)
+++ plugins/rt_topo/crbs_route.c	(revision 1448)
@@ -176,13 +176,28 @@
 }
 */
 
+/* toa must be an arc */
+static int crbs_is_spiral(usrch_a_star_t *ctx, grbs_detached_addr_t *froma, grbs_addr_t *toa)
+{
+	usrch_a_star_node_t *it;
+	grbs_detached_addr_t *da;
+
+#warning TODO: we should probably allow real spirals and deny only on the same orbit (some maze setup may have legit spiral)
+
+	for(da = usrch_a_star_path_first_from(ctx, froma, &it); da != NULL; da = usrch_a_star_path_next(ctx, &it)) {
+		if (da->pt == toa->obj.arc->parent_pt)
+			return 1;
+	}
+}
+
 static int hop_cnt = 0;
 
 /* Attempt to create a grbs path segment from curr to pt:adir. If fails, return
    NULL. If succeeds, remove the path segment from the grbs context, add a
    detached address of it to the hash and return it. */
-static grbs_detached_addr_t *crbs_next_hop(crbs_t *crbs, grbs_detached_addr_t *curr, crbs_point_t *pt, grbs_arc_dir_t adir)
+static grbs_detached_addr_t *crbs_next_hop(usrch_a_star_t *ctx, grbs_detached_addr_t *curr, crbs_point_t *pt, grbs_arc_dir_t adir)
 {
+	crbs_t *crbs = ctx->user_data;
 	grbs_addr_t *froma, *toa;
 	grbs_2net_t *gtn = crbs->routing_tn;
 	grbs_detached_addr_t *res = NULL, dtmp[3];
@@ -241,6 +256,16 @@
 			}
 		}
 
+		if ((adir == GRBS_ADIR_CONVEX_CCW) || (adir == GRBS_ADIR_CONVEX_CW)) {
+			if (crbs_is_spiral(ctx, curr, toa)) {
+				printf("   INVALID spiral: P%ld\n", froma->obj.arc->parent_pt == NULL ? -1 : froma->obj.arc->parent_pt->uid);
+				grbs_path_cleanup_addr(&crbs->grbs, toa);
+				grbs_path_cleanup_addr(&crbs->grbs, froma);
+				return NULL;
+			}
+		}
+
+
 		grbs_detach_addr(&crbs->grbs, dtmp, toa);
 		key = grbs_det_addr_to_key(dtmp);
 		e = htad_getentry(&crbs->addrs, key);
@@ -306,7 +331,7 @@
 
 		if (pt == crbs->target->pt->user_data) { /* quick lane for reaching the target */
 			if (crbs_trace_ast) printf(" try from %s P%ld to TARGET P%ld", from_type, curr->pt->uid, pt->gpt->uid);
-			next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_INC);
+			next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_INC);
 			if (next != NULL) {
 				a->pt_idx = a->pts.used; /* don't consider detours from the current node if target node can be reached directly */
 				if (crbs_trace_ast) printf(" -> ok\n");
@@ -339,11 +364,11 @@
 			/* prefer concave over convex; order matters when reaching target: first
 			   valid solution will stop the search */
 			switch(a->grbs_idx) {
-				case 0: if (crbs_trace_ast) printf(" concave ccw"); next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_CONCAVE_CCW); break;
-				case 1: if (crbs_trace_ast) printf(" concave cw"); next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_CONCAVE_CW);  break;
-				case 2: if (crbs_trace_ast) printf(" vconcave"); next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_VCONCAVE); break;
-				case 3: if (crbs_trace_ast) printf(" convex ccw"); next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_CONVEX_CCW); break;
-				case 4: if (crbs_trace_ast) printf(" convex cw"); next = crbs_next_hop(crbs, curr, pt, GRBS_ADIR_CONVEX_CW); break;
+				case 0: if (crbs_trace_ast) printf(" concave ccw"); next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_CONCAVE_CCW); break;
+				case 1: if (crbs_trace_ast) printf(" concave cw"); next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_CONCAVE_CW);  break;
+				case 2: if (crbs_trace_ast) printf(" vconcave"); next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_VCONCAVE); break;
+				case 3: if (crbs_trace_ast) printf(" convex ccw"); next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_CONVEX_CCW); break;
+				case 4: if (crbs_trace_ast) printf(" convex cw"); next = crbs_next_hop(ctx, curr, pt, GRBS_ADIR_CONVEX_CW); break;
 			}
 
 			a->grbs_idx++;