diff --git a/icetime/Makefile b/icetime/Makefile
index aead84a..2eef844 100644
--- a/icetime/Makefile
+++ b/icetime/Makefile
@@ -1,5 +1,4 @@
 # CXX = clang
-CXX ?= clang
 LDLIBS = -lm -lstdc++
 CXXFLAGS = -MD -O0 -ggdb -Wall -std=c++11 -I/usr/local/include
 CC = $(CXX)
diff --git a/icetime/icetime.cc b/icetime/icetime.cc
index 61a63ed..f59ad12 100644
--- a/icetime/icetime.cc
+++ b/icetime/icetime.cc
@@ -32,91 +32,55 @@ struct net_segment_name
 };
 
 std::map<net_segment_name, int> segment_to_net;
-std::vector<std::set<net_segment_name>> net_to_segments;
+std::map<int, std::set<net_segment_name>> net_to_segments;
 std::map<int, std::set<int>> net_buffers, net_rbuffers, net_routing;
+std::map<std::pair<int, int>, std::pair<int, int>> connection_pos;
 std::set<int> used_nets;
 
-void read_chipdb()
+// netlist_cells[cell_name][port_name] = port_expr
+std::map<std::string, std::map<std::string, std::string>> netlist_cells;
+std::map<std::string, std::string> netlist_cell_types;
+
+std::string vstringf(const char *fmt, va_list ap)
 {
-	char buffer[1024];
-	snprintf(buffer, 1024, "/usr/local/share/icebox/chipdb-%s.txt", config_device.c_str());
+	std::string string;
+	char *str = NULL;
 
-	FILE *fdb = fopen(buffer, "r");
-	if (fdb == nullptr) {
-		perror("Can't open chipdb file");
-		exit(1);
+#ifdef _WIN32
+	int sz = 64, rc;
+	while (1) {
+		va_list apc;
+		va_copy(apc, ap);
+		str = (char*)realloc(str, sz);
+		rc = vsnprintf(str, sz, fmt, apc);
+		va_end(apc);
+		if (rc >= 0 && rc < sz)
+			break;
+		sz *= 2;
+	}
+#else
+	if (vasprintf(&str, fmt, ap) < 0)
+		str = NULL;
+#endif
+
+	if (str != NULL) {
+		string = str;
+		free(str);
 	}
 
+	return string;
+}
 
-	std::string mode;
-	int current_net = -1;
-	std::string thiscfg;
+std::string stringf(const char *fmt, ...)
+{
+	std::string string;
+	va_list ap;
 
-	while (fgets(buffer, 1024, fdb))
-	{
-		if (buffer[0] == '#')
-			continue;
+	va_start(ap, fmt);
+	string = vstringf(fmt, ap);
+	va_end(ap);
 
-		const char *tok = strtok(buffer, " \t\r\n");
-		if (tok == nullptr)
-			continue;
-
-		if (tok[0] == '.')
-		{
-			mode = tok;
-
-			if (mode == ".net")
-			{
-				current_net = atoi(strtok(nullptr, " \t\r\n"));
-				if (current_net >= int(net_to_segments.size()))
-					net_to_segments.resize(current_net+1);
-			}
-
-			if (mode == ".buffer" || mode == ".routing")
-			{
-				int tile_x = atoi(strtok(nullptr, " \t\r\n"));
-				int tile_y = atoi(strtok(nullptr, " \t\r\n"));
-				current_net = atoi(strtok(nullptr, " \t\r\n"));
-
-				thiscfg = "";
-				while ((tok = strtok(nullptr, " \t\r\n")) != nullptr) {
-					int bit_row, bit_col, rc;
-					rc = sscanf(tok, "B%d[%d]", &bit_row, &bit_col);
-					assert(rc == 2);
-					thiscfg.push_back(config_bits[tile_x][tile_y][bit_row][bit_col] ? '1' : '0');
-				}
-			}
-
-			continue;
-		}
-
-		if (mode == ".net") {
-			int tile_x = atoi(tok);
-			int tile_y = atoi(strtok(nullptr, " \t\r\n"));
-			std::string segment_name = strtok(nullptr, " \t\r\n");
-			net_segment_name seg(tile_x, tile_y, segment_name);
-			segment_to_net[seg] = current_net;
-			net_to_segments[current_net].insert(seg);
-		}
-
-		if (mode == ".buffer" && !strcmp(tok, thiscfg.c_str())) {
-			int other_net = atoi(strtok(nullptr, " \t\r\n"));
-			net_rbuffers[current_net].insert(other_net);
-			net_buffers[other_net].insert(current_net);
-			used_nets.insert(current_net);
-			used_nets.insert(other_net);
-		}
-
-		if (mode == ".routing" && !strcmp(tok, thiscfg.c_str())) {
-			int other_net = atoi(strtok(nullptr, " \t\r\n"));
-			net_routing[current_net].insert(other_net);
-			net_routing[other_net].insert(current_net);
-			used_nets.insert(current_net);
-			used_nets.insert(other_net);
-		}
-	}
-
-	fclose(fdb);
+	return string;
 }
 
 void read_config()
@@ -173,6 +137,190 @@ void read_config()
 	}
 }
 
+void read_chipdb()
+{
+	char buffer[1024];
+	snprintf(buffer, 1024, "/usr/local/share/icebox/chipdb-%s.txt", config_device.c_str());
+
+	FILE *fdb = fopen(buffer, "r");
+	if (fdb == nullptr) {
+		perror("Can't open chipdb file");
+		exit(1);
+	}
+
+
+	std::string mode;
+	int current_net = -1;
+	int tile_x = -1, tile_y = -1;
+	std::string thiscfg;
+
+	while (fgets(buffer, 1024, fdb))
+	{
+		if (buffer[0] == '#')
+			continue;
+
+		const char *tok = strtok(buffer, " \t\r\n");
+		if (tok == nullptr)
+			continue;
+
+		if (tok[0] == '.')
+		{
+			mode = tok;
+
+			if (mode == ".net")
+			{
+				current_net = atoi(strtok(nullptr, " \t\r\n"));
+				continue;
+			}
+
+			if (mode == ".buffer" || mode == ".routing")
+			{
+				tile_x = atoi(strtok(nullptr, " \t\r\n"));
+				tile_y = atoi(strtok(nullptr, " \t\r\n"));
+				current_net = atoi(strtok(nullptr, " \t\r\n"));
+
+				thiscfg = "";
+				while ((tok = strtok(nullptr, " \t\r\n")) != nullptr) {
+					int bit_row, bit_col, rc;
+					rc = sscanf(tok, "B%d[%d]", &bit_row, &bit_col);
+					assert(rc == 2);
+					thiscfg.push_back(config_bits[tile_x][tile_y][bit_row][bit_col] ? '1' : '0');
+				}
+				continue;
+			}
+
+			continue;
+		}
+
+		if (mode == ".net") {
+			int tile_x = atoi(tok);
+			int tile_y = atoi(strtok(nullptr, " \t\r\n"));
+			std::string segment_name = strtok(nullptr, " \t\r\n");
+			net_segment_name seg(tile_x, tile_y, segment_name);
+			segment_to_net[seg] = current_net;
+			net_to_segments[current_net].insert(seg);
+		}
+
+		if (mode == ".buffer" && !strcmp(tok, thiscfg.c_str())) {
+			int other_net = atoi(strtok(nullptr, " \t\r\n"));
+			net_rbuffers[current_net].insert(other_net);
+			net_buffers[other_net].insert(current_net);
+			connection_pos[std::pair<int, int>(current_net, other_net)] =
+					connection_pos[std::pair<int, int>(other_net, current_net)] =
+					std::pair<int, int>(tile_x, tile_y);
+			used_nets.insert(current_net);
+			used_nets.insert(other_net);
+		}
+
+		if (mode == ".routing" && !strcmp(tok, thiscfg.c_str())) {
+			int other_net = atoi(strtok(nullptr, " \t\r\n"));
+			net_routing[current_net].insert(other_net);
+			net_routing[other_net].insert(current_net);
+			connection_pos[std::pair<int, int>(current_net, other_net)] =
+					connection_pos[std::pair<int, int>(other_net, current_net)] =
+					std::pair<int, int>(tile_x, tile_y);
+			used_nets.insert(current_net);
+			used_nets.insert(other_net);
+		}
+	}
+
+	fclose(fdb);
+
+	// purge unused nets from memory
+	int max_net = net_to_segments.rbegin()->first;
+	for (int net = 0; net <= max_net; net++)
+	{
+		if (used_nets.count(net))
+			continue;
+
+		for (auto seg : net_to_segments[net])
+			segment_to_net.erase(seg);
+		net_to_segments.erase(net);
+
+		for (auto other : net_buffers[net])
+			net_rbuffers[other].erase(net);
+		net_buffers.erase(net);
+
+		for (auto other : net_rbuffers[net])
+			net_buffers[other].erase(net);
+		net_rbuffers.erase(net);
+
+		for (auto other : net_routing[net])
+			net_routing[other].erase(net);
+		net_routing.erase(net);
+	}
+
+#if 1
+	for (int net : used_nets)
+	{
+		printf("// NET %d:\n", net);
+		for (auto seg : net_to_segments[net])
+			printf("//  SEG %d %d %s\n", seg.tile_x, seg.tile_y, seg.segment_name.c_str());
+		for (auto other : net_buffers[net])
+			printf("//  BUFFER %d %d %d\n", connection_pos[std::pair<int, int>(net, other)].first,
+					connection_pos[std::pair<int, int>(net, other)].second, other);
+		for (auto other : net_rbuffers[net])
+			printf("//  RBUFFER %d %d %d\n", connection_pos[std::pair<int, int>(net, other)].first,
+					connection_pos[std::pair<int, int>(net, other)].second, other);
+		for (auto other : net_routing[net])
+			printf("//  ROUTE %d %d %d\n", connection_pos[std::pair<int, int>(net, other)].first,
+					connection_pos[std::pair<int, int>(net, other)].second, other);
+	}
+#endif
+}
+
+std::string make_seg_pre_io(int x, int y, int z)
+{
+	auto cell = stringf("pre_io_%d_%d_%d", x, y, z);
+
+	if (netlist_cell_types.count(cell))
+		return cell;
+
+	netlist_cell_types[cell] = "PRE_IO";
+	netlist_cells[cell]["PADIN"] = stringf("io_pad_%d_%d_%d_dout", x, y, z);
+	netlist_cells[cell]["PADOUT"] = stringf("io_pad_%d_%d_%d_din", x, y, z);
+	netlist_cells[cell]["PADOEN"] = stringf("io_pad_%d_%d_%d_oe", x, y, z);
+	netlist_cells[cell]["LATCHINPUTVALUE"] = "";
+	netlist_cells[cell]["CLOCKENABLE"] = "";
+	netlist_cells[cell]["INPUTCLK"] = "";
+	netlist_cells[cell]["OUTPUTCLK"] = "";
+	netlist_cells[cell]["OUTPUTENABLE"] = "";
+	netlist_cells[cell]["DOUT1"] = "";
+	netlist_cells[cell]["DOUT0"] = "";
+	netlist_cells[cell]["DIN1"] = "";
+	netlist_cells[cell]["DIN0"] = "";
+
+	fprintf(fout, "  wire io_pad_%d_%d_%d_din;\n", x, y, z);
+	fprintf(fout, "  wire io_pad_%d_%d_%d_dout;\n", x, y, z);
+	fprintf(fout, "  wire io_pad_%d_%d_%d_oe;\n", x, y, z);
+	fprintf(fout, "  (* keep *) wire io_pad_%d_%d_%d_pin;\n", x, y, z);
+	fprintf(fout, "  IO_PAD io_pad_%d_%d_%d (\n", x, y, z);
+	fprintf(fout, "    .DIN(io_pad_%d_%d_%d_din),\n", x, y, z);
+	fprintf(fout, "    .DOUT(io_pad_%d_%d_%d_dout),\n", x, y, z);
+	fprintf(fout, "    .OE(io_pad_%d_%d_%d_oe),\n", x, y, z);
+	fprintf(fout, "    .PACKAGEPIN(io_pad_%d_%d_%d_pin)\n", x, y, z);
+	fprintf(fout, "  );\n");
+
+	return cell;
+}
+
+void make_seg_cell(int net, const net_segment_name &seg)
+{
+	int a, b;
+
+	if (sscanf(seg.segment_name.c_str(), "io_%d/D_IN_%d", &a, &b) == 2) {
+		auto cell = make_seg_pre_io(seg.tile_x, seg.tile_y, a);
+		netlist_cells[cell][stringf("DIN%d", b)] = stringf("net_%d", net);
+		return;
+	}
+
+	if (sscanf(seg.segment_name.c_str(), "io_%d/D_OUT_%d", &a, &b) == 2) {
+		auto cell = make_seg_pre_io(seg.tile_x, seg.tile_y, a);
+		netlist_cells[cell][stringf("DOUT%d", b)] = stringf("net_%d", net);
+		return;
+	}
+}
+
 void help(const char *cmd)
 {
 	printf("\n");
@@ -221,5 +369,26 @@ int main(int argc, char **argv)
 	printf("// Reading chipdb file..\n");
 	read_chipdb();
 
+	fprintf(fout, "module chip;\n");
+
+	for (int net : used_nets)
+		fprintf(fout, "  wire net_%d;\n", net);
+
+	for (int net : used_nets)
+	for (auto seg : net_to_segments[net])
+		make_seg_cell(net, seg);
+
+	for (auto it : netlist_cell_types) {
+		const char *sep = "";
+		fprintf(fout, "  %s %s (", it.second.c_str(), it.first.c_str());
+		for (auto port : netlist_cells[it.first]) {
+			fprintf(fout, "%s\n    .%s(%s)", sep, port.first.c_str(), port.second.c_str());
+			sep = ",";
+		}
+		fprintf(fout, "\n  );\n");
+	}
+
+	fprintf(fout, "endmodule\n");
+
 	return 0;
 }