diff --git a/common/design_utils.cc b/common/design_utils.cc
index bdf5ca5..10212a0 100644
--- a/common/design_utils.cc
+++ b/common/design_utils.cc
@@ -88,7 +88,7 @@
         NPNR_ASSERT(net->driver.cell == nullptr);
         net->driver.cell = cell;
         net->driver.port = port_name;
-    } else if (port.type == PORT_IN) {
+    } else if (port.type == PORT_IN || port.type == PORT_INOUT) {
         PortRef user;
         user.cell = cell;
         user.port = port_name;
@@ -146,4 +146,14 @@
     cell->ports[new_name] = pi;
 }
 
+void rename_net(Context *ctx, NetInfo *net, IdString new_name)
+{
+    if (net == nullptr)
+        return;
+    NPNR_ASSERT(!ctx->nets.count(new_name));
+    std::swap(ctx->nets[net->name], ctx->nets[new_name]);
+    ctx->nets.erase(net->name);
+    net->name = new_name;
+}
+
 NEXTPNR_NAMESPACE_END
diff --git a/common/design_utils.h b/common/design_utils.h
index 3eb9024..1ae1d64 100644
--- a/common/design_utils.h
+++ b/common/design_utils.h
@@ -94,6 +94,9 @@
 // Rename a port if it exists on a cell
 void rename_port(Context *ctx, CellInfo *cell, IdString old_name, IdString new_name);
 
+// Rename a net without invalidating pointers to it
+void rename_net(Context *ctx, NetInfo *net, IdString new_name);
+
 void print_utilisation(const Context *ctx);
 
 NEXTPNR_NAMESPACE_END
diff --git a/ecp5/cells.cc b/ecp5/cells.cc
index 37b6ac8..b70b412 100644
--- a/ecp5/cells.cc
+++ b/ecp5/cells.cc
@@ -416,7 +416,25 @@
     } else {
         NPNR_ASSERT(false);
     }
-    NetInfo *donet = trio->ports.at(ctx->id("I")).net;
+    NetInfo *donet = trio->ports.at(ctx->id("I")).net, *dinet = trio->ports.at(ctx->id("O")).net;
+
+    // Rename I/O nets to avoid conflicts
+    if (donet != nullptr)
+        rename_net(ctx, donet, ctx->id(donet->name.str(ctx) + "$TRELLIS_IO_OUT"));
+    if (dinet != nullptr)
+        rename_net(ctx, dinet, ctx->id(dinet->name.str(ctx) + "$TRELLIS_IO_IN"));
+
+    // Create a new top port net for accurate IO timing analysis and simulation netlists
+    if (ctx->ports.count(nxio->name)) {
+        IdString tn_netname = nxio->name;
+        NPNR_ASSERT(!ctx->nets.count(tn_netname));
+        std::unique_ptr<NetInfo> toplevel_net{new NetInfo};
+        toplevel_net->name = tn_netname;
+        connect_port(ctx, toplevel_net.get(), trio, ctx->id("B"));
+        ctx->ports[nxio->name].net = toplevel_net.get();
+        ctx->nets[tn_netname] = std::move(toplevel_net);
+    }
+
     CellInfo *tbuf = net_driven_by(
             ctx, donet, [](const Context *ctx, const CellInfo *cell) { return cell->type == ctx->id("$_TBUF_"); },
             ctx->id("Y"));
diff --git a/ecp5/pack.cc b/ecp5/pack.cc
index 244a79d..00ed891 100644
--- a/ecp5/pack.cc
+++ b/ecp5/pack.cc
@@ -362,8 +362,7 @@
                     for (auto &port : ci->ports)
                         disconnect_port(ctx, ci, port.first);
                 } else if (trio != nullptr) {
-                    // Trivial case, TRELLIS_IO used. Just destroy the net and the
-                    // iobuf
+                    // Trivial case, TRELLIS_IO used. Just remove the IOBUF
                     log_info("%s feeds TRELLIS_IO %s, removing %s %s.\n", ci->name.c_str(ctx), trio->name.c_str(ctx),
                              ci->type.c_str(ctx), ci->name.c_str(ctx));
 
@@ -384,14 +383,6 @@
                                 std::swap(net->clkconstr, onet->clkconstr);
                             }
                         }
-                        ctx->nets.erase(net->name);
-                        trio->ports.at(ctx->id("B")).net = nullptr;
-                    }
-                    if (ci->type == ctx->id("$nextpnr_iobuf")) {
-                        NetInfo *net2 = ci->ports.at(ctx->id("I")).net;
-                        if (net2 != nullptr) {
-                            ctx->nets.erase(net2->name);
-                        }
                     }
                 } else if (drives_top_port(ionet, tp)) {
                     log_info("%s feeds %s %s.%s, removing %s %s.\n", ci->name.c_str(ctx), tp.cell->type.c_str(ctx),
@@ -414,7 +405,8 @@
                     new_cells.push_back(std::move(tr_cell));
                     trio = new_cells.back().get();
                 }
-
+                for (auto port : ci->ports)
+                    disconnect_port(ctx, ci, port.first);
                 packed_cells.insert(ci->name);
                 if (trio != nullptr) {
                     for (const auto &attr : ci->attrs)