diff --git a/himbaechel/uarch/ng-ultra/gen/arch_gen.py b/himbaechel/uarch/ng-ultra/gen/arch_gen.py
index 14295736..ae66d002 100644
--- a/himbaechel/uarch/ng-ultra/gen/arch_gen.py
+++ b/himbaechel/uarch/ng-ultra/gen/arch_gen.py
@@ -381,12 +381,6 @@ def create_tile_types(ch: Chip, bels, bel_pins, crossbars, interconnects, muxes,
                             pd = tt.create_pip(f"{name}."+inp,f"{name}."+out,"MATRIX_PIP")
                             pd.extra_data = PipExtraData(ch.strs.id(f"{name}."+inp),PIP_EXTRA_MUX,int(inp[1:])-1,int(out[1:])-1)
 
-                elif (tile_type.startswith("IOB") and bel=="DFR"):
-                    by = tt.create_pip(f"{name}.I",f"{name}.O","BYPASS")
-                    by.extra_data = PipExtraData(ch.strs.id(name),PIP_EXTRA_BYPASS,0,0)
-                elif (tile_type.startswith("IOB") and bel=="DDFR"):
-                    by = tt.create_pip(f"{name}.I",f"{name}.O","BYPASS")
-                    by.extra_data = PipExtraData(ch.strs.id(name),PIP_EXTRA_BYPASS,0,0)
                 elif (tile_type.startswith("CKG") and bel=="WFG"):
                     by = tt.create_pip(f"{name}.ZI",f"{name}.ZO","BYPASS")
                     by.extra_data = PipExtraData(ch.strs.id(name),PIP_EXTRA_BYPASS,0,0)
diff --git a/himbaechel/uarch/ng-ultra/ng_ultra.cc b/himbaechel/uarch/ng-ultra/ng_ultra.cc
index 66a25f2e..677fa92e 100644
--- a/himbaechel/uarch/ng-ultra/ng_ultra.cc
+++ b/himbaechel/uarch/ng-ultra/ng_ultra.cc
@@ -114,7 +114,7 @@ void NgUltraImpl::postRoute()
     ctx->assignArchInfo();
     log_break();
     log_info("Resources spent on routing:\n");
-    int dff_bypass = 0, fe_new = 0, wfg_bypass = 0, gck_bypass = 0, ddfr_bypass = 0;
+    int dff_bypass = 0, fe_new = 0, wfg_bypass = 0, gck_bypass = 0;
     for (auto &net : ctx->nets) {
         NetInfo *ni = net.second.get();
         for (auto &w : ni->wires) {
@@ -132,7 +132,6 @@ void NgUltraImpl::postRoute()
                         if (type==id_BEYOND_FE) fe_new++;
                     }
                     CellInfo *cell = ctx->getBoundBelCell(bel);
-                    std::string bel_name = ctx->getBelName(cell->bel)[1].c_str(ctx);
                     switch(type.index) {
                         case id_BEYOND_FE.index : 
                                             dff_bypass++;
@@ -144,26 +143,6 @@ void NgUltraImpl::postRoute()
                                             cell->setParam(ctx->id("type"), Property("WFB"));
                                             break;
                         case id_GCK.index : gck_bypass++; break;
-                        case id_DDFR.index :
-                        case id_DFR.index : ddfr_bypass++;
-                                            {
-                                                Loc loc = ctx->getBelLocation(bel);
-                                                cell->setParam(ctx->id("type"), Property("BFR"));
-                                                cell->setParam(ctx->id("mode"), Property(2, 2));
-                                                cell->setParam(ctx->id("data_inv"), Property(0, 1));
-                                                if (boost::ends_with(bel_name, "CD")) {
-                                                    loc.z -= 3;
-                                                } else if (boost::ends_with(bel_name, "OD")) {
-                                                    loc.z -= 2;
-                                                } else {
-                                                    loc.z -= 1;
-                                                }
-                                                CellInfo *iob = ctx->getBoundBelCell(ctx->getBelByLocation(loc));
-                                                if (!iob || iob->params.count(ctx->id("iobname"))==0)
-                                                    log_error("IOB for '%s' must have iobname defined.\n", cell->name.c_str(ctx));
-                                                cell->setParam(ctx->id("iobname"), iob->params[ctx->id("iobname")]);
-                                            }                                    
-                                            break;
                         default:
                             log_error("Unmaped bel type '%s' for routing\n",type.c_str(ctx));
                     }
@@ -174,7 +153,6 @@ void NgUltraImpl::postRoute()
     log_info("    %6d DFFs used as BFF (%d new allocated FEs)\n", dff_bypass, fe_new);
     log_info("    %6d WFGs used as WFB\n", wfg_bypass);
     log_info("    %6d GCK\n", gck_bypass);
-    log_info("    %6d DFR/DDFR as BFR\n", ddfr_bypass);
 
     // Handle LUT permutation
     for (auto &cell : ctx->cells) {
diff --git a/himbaechel/uarch/ng-ultra/pack.cc b/himbaechel/uarch/ng-ultra/pack.cc
index 8875a44b..42d8d5eb 100644
--- a/himbaechel/uarch/ng-ultra/pack.cc
+++ b/himbaechel/uarch/ng-ultra/pack.cc
@@ -44,6 +44,9 @@ inline bool is_dff(const BaseCtx *ctx, const CellInfo *cell) { return cell->type
 // Return true if a cell is a FE
 inline bool is_fe(const BaseCtx *ctx, const CellInfo *cell) { return cell->type == id_BEYOND_FE; }
 
+// Return true if a cell is a DFR
+inline bool is_dfr(const BaseCtx *ctx, const CellInfo *cell) { return cell->type == id_NX_DFR; }
+
 // Process the contents of packed_cells
 void NgUltraPacker::flush_cells()
 {
@@ -397,31 +400,106 @@ void NgUltraPacker::pack_iobs(void)
         ci.type = new_type;
 
         ctx->bindBel(bel, &ci, PlaceStrength::STRENGTH_LOCKED);
+        to_update.push_back(&ci);
+    }
+    int dfr_as_bfr = 0, ddrf_as_bfr = 0;
+    for (auto cell : to_update) {
+        NetInfo *c_net = cell->getPort(id_C);
+        if (!c_net)
+            log_error("C input of IO primitive %s must be connected.\n", cell->name.c_str(ctx));
+        if (c_net->name == ctx->id("$PACKER_GND") && !cell->getPort(id_O))
+            log_error("O port of IO primitive %s must be connected.\n", cell->name.c_str(ctx));
+        if (c_net->name == ctx->id("$PACKER_VCC") && !cell->getPort(id_I))
+            log_error("I port of IO primitive %s must be connected.\n", cell->name.c_str(ctx));
+        if (!cell->getPort(id_I) && !cell->getPort(id_O))
+            log_error("I or O port of IO primitive %s must be connected.\n", cell->name.c_str(ctx));
 
-        NetInfo *net = ci.getPort(id_C);
-        if (net && net->name.in(ctx->id("$PACKER_GND"), ctx->id("$PACKER_VCC")))
         {
-            to_update.push_back(&ci);
+            CellInfo *iod = net_driven_by(ctx, c_net, is_dfr, id_O);
+            if (iod && c_net->users.entries()!=1)
+                log_error("NX_DFR '%s can only directly drive IOB.\n", iod->name.c_str(ctx));
+            if (!iod) {
+                if (cell->type==id_IOTP) ddrf_as_bfr++; else dfr_as_bfr++;
+                iod = create_cell_ptr((cell->type==id_IOTP) ? id_DDFR : id_DFR, ctx->id(cell->name.str(ctx) + "$iod_cd"));
+                NetInfo *new_out = ctx->createNet(ctx->id(iod->name.str(ctx) + "$O"));
+                iod->setParam(ctx->id("iobname"),str_or_default(cell->params, ctx->id("iobname"), ""));
+                iod->setParam(ctx->id("type"), Property("BFR"));
+                cell->disconnectPort(id_C);
+                if (c_net->name == ctx->id("$PACKER_GND"))
+                    iod->setParam(ctx->id("mode"), Property(0, 2));
+                else if (c_net->name == ctx->id("$PACKER_VCC"))
+                    iod->setParam(ctx->id("mode"), Property(1, 2));
+                else {
+                    iod->connectPort(id_I, c_net);
+                    iod->setParam(ctx->id("mode"), Property(2, 2));
+                    iod->setParam(ctx->id("data_inv"), Property(0, 1));
+                }
+                iod->connectPort(id_O, new_out);
+                cell->connectPort(id_C,new_out);
+            } else log_error("TODO handle DFR");
+            Loc cd_loc = cell->getLocation();
+            cd_loc.z += 3;
+            BelId bel = ctx->getBelByLocation(cd_loc);
+            ctx->bindBel(bel, iod, PlaceStrength::STRENGTH_LOCKED);
+        }
+        NetInfo *i_net = cell->getPort(id_I);
+        if (i_net) {
+            CellInfo *iod = net_driven_by(ctx, i_net, is_dfr, id_O);
+            if (iod && i_net->users.entries()!=1)
+                log_error("NX_DFR '%s can only directly drive IOB.\n", iod->name.c_str(ctx));
+            if (!iod) {
+                if (cell->type==id_IOTP) ddrf_as_bfr++; else dfr_as_bfr++;
+                iod = create_cell_ptr((cell->type==id_IOTP) ? id_DDFR : id_DFR, ctx->id(cell->name.str(ctx) + "$iod_od"));
+                NetInfo *new_out = ctx->createNet(ctx->id(iod->name.str(ctx) + "$O"));
+                iod->setParam(ctx->id("iobname"),str_or_default(cell->params, ctx->id("iobname"), ""));
+                iod->setParam(ctx->id("type"), Property("BFR"));
+                cell->disconnectPort(id_I);
+                if (i_net->name == ctx->id("$PACKER_GND"))
+                    iod->setParam(ctx->id("mode"), Property(0, 2));
+                else if (i_net->name == ctx->id("$PACKER_VCC"))
+                    iod->setParam(ctx->id("mode"), Property(1, 2));
+                else {
+                    iod->connectPort(id_I, i_net);
+                    iod->setParam(ctx->id("mode"), Property(2, 2));
+                    iod->setParam(ctx->id("data_inv"), Property(0, 1));
+                }
+                iod->connectPort(id_O, new_out);
+                cell->connectPort(id_I,new_out);
+            } else log_error("TODO handle DFR");
+            Loc cd_loc = cell->getLocation();
+            cd_loc.z += 2;
+            BelId bel = ctx->getBelByLocation(cd_loc);
+            ctx->bindBel(bel, iod, PlaceStrength::STRENGTH_LOCKED);
+        }
+
+        NetInfo *o_net = cell->getPort(id_O);
+        if (o_net) {
+            CellInfo *iod = net_only_drives(ctx, o_net, is_dfr, id_I, true);
+            if (!iod) {
+                if (cell->type==id_IOTP) ddrf_as_bfr++; else dfr_as_bfr++;
+                iod = create_cell_ptr((cell->type==id_IOTP) ? id_DDFR : id_DFR, ctx->id(cell->name.str(ctx) + "$iod_id"));
+                NetInfo *new_in = ctx->createNet(ctx->id(iod->name.str(ctx) + "$I"));
+                iod->setParam(ctx->id("iobname"),str_or_default(cell->params, ctx->id("iobname"), ""));
+                iod->setParam(ctx->id("type"), Property("BFR"));
+                cell->disconnectPort(id_O);
+                iod->connectPort(id_O, o_net);
+                iod->setParam(ctx->id("mode"), Property(2, 2));
+                iod->setParam(ctx->id("data_inv"), Property(0, 1));
+                iod->connectPort(id_I, new_in);
+                cell->connectPort(id_O,new_in);
+            } else log_error("TODO handle DFR");
+            Loc cd_loc = cell->getLocation();
+            cd_loc.z += 1;
+            BelId bel = ctx->getBelByLocation(cd_loc);
+            ctx->bindBel(bel, iod, PlaceStrength::STRENGTH_LOCKED);
         }
     }
-    for (auto cell : to_update) {
-        CellInfo *iod_cd = create_cell_ptr((cell->type==id_IOTP) ? id_DDFR : id_DFR, ctx->id(cell->name.str(ctx) + "$iod_cd"));
-        cell->disconnectPort(id_C);
-        NetInfo *new_out = ctx->createNet(ctx->id(iod_cd->name.str(ctx) + "$O"));
-        iod_cd->connectPort(id_O, new_out);
-        iod_cd->setParam(ctx->id("iobname"),str_or_default(cell->params, ctx->id("iobname"), ""));
-        iod_cd->setParam(ctx->id("type"), Property("BFR"));
-        if (cell->params[ctx->id("type")].as_string()=="IP")
-            iod_cd->setParam(ctx->id("mode"), Property(0, 2));
-        else
-            iod_cd->setParam(ctx->id("mode"), Property(1, 2));
-        cell->connectPort(id_C,new_out);
-        Loc loc = cell->getLocation();
-        loc.z += 3;
-        BelId bel = ctx->getBelByLocation(loc);
-        ctx->bindBel(bel, iod_cd, PlaceStrength::STRENGTH_LOCKED);
-    }
+    if (dfr_as_bfr)
+        log_info("    %6d DFRs used as BFR\n", dfr_as_bfr);
+    if (ddrf_as_bfr)
+        log_info("    %6d DDFRs used as BFR\n", ddrf_as_bfr);
 }
+
 void NgUltraPacker::pack_ioms(void)
 {
     log_info("Pack IOMs...\n");