diff --git a/CHANGELOG b/CHANGELOG
index 113aae820..f7774cb9e 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -26,6 +26,11 @@ Yosys 0.9 .. Yosys 0.9-dev
     - Added automatic gzip compression (based on filename extension) for backends
     - Improve attribute and parameter encoding in JSON to avoid ambiguities between
       bit vectors and strings containing [01xz]*
+    - Added "clkbufmap" pass
+    - Added "synth_xilinx -family xc6s" for Spartan 6 support (experimental)
+    - Added "synth_xilinx -ise" (experimental)
+    - Added "synth_xilinx -iopad"
+    - "synth_xilinx" now automatically inserts clock buffers (add -noclkbuf to disable)
     - Improvements in pmgen: subpattern and recursive matches
     - Added "opt_share" pass, run as part of "opt -full"
     - Added "ice40_wrapcarry" to encapsulate SB_LUT+SB_CARRY pairs for techmapping
diff --git a/README.md b/README.md
index 606c4942e..38ca77862 100644
--- a/README.md
+++ b/README.md
@@ -332,6 +332,21 @@ Verilog Attributes and non-standard features
   that represent module parameters or localparams (when the HDL front-end
   is run in -pwires mode).
 
+- The ``clkbuf_driver`` attribute can be set on an output port of a blackbox
+  module to mark it as a clock buffer output, and thus prevent ``clkbufmap``
+  from inserting another clock buffer on a net driven by such output.
+
+- The ``clkbuf_sink`` attribute can be set on an input port of a module to
+  request clock buffer insertion by the ``clkbufmap`` pass.
+
+- The ``clkbuf_inhibit`` is the default attribute to set on a wire to prevent
+  automatic clock buffer insertion by ``clkbufmap``. This behaviour can be
+  overridden by providing a custom selection to ``clkbufmap``.
+
+- The ``iopad_external_pin`` attribute on a blackbox module's port marks
+  it as the external-facing pin of an I/O pad, and prevents ``iopadmap``
+  from inserting another pad cell on it.
+
 - In addition to the ``(* ... *)`` attribute syntax, Yosys supports
   the non-standard ``{* ... *}`` attribute syntax to set default attributes
   for everything that comes after the ``{* ... *}`` statement. (Reset
diff --git a/examples/mimas2/run_yosys.ys b/examples/mimas2/run_yosys.ys
index b3204b1ca..b48877811 100644
--- a/examples/mimas2/run_yosys.ys
+++ b/examples/mimas2/run_yosys.ys
@@ -1,4 +1,3 @@
 read_verilog example.v
-synth_xilinx -top example -family xc6s
-iopadmap -bits -outpad OBUF I:O -inpad IBUF O:I
+synth_xilinx -top example -family xc6s -ise
 write_edif -pvector bra example.edif
diff --git a/passes/techmap/Makefile.inc b/passes/techmap/Makefile.inc
index 56f05eca4..631a80aa5 100644
--- a/passes/techmap/Makefile.inc
+++ b/passes/techmap/Makefile.inc
@@ -16,6 +16,7 @@ endif
 
 ifneq ($(SMALL),1)
 OBJS += passes/techmap/iopadmap.o
+OBJS += passes/techmap/clkbufmap.o
 OBJS += passes/techmap/hilomap.o
 OBJS += passes/techmap/extract.o
 OBJS += passes/techmap/extract_fa.o
diff --git a/passes/techmap/clkbufmap.cc b/passes/techmap/clkbufmap.cc
new file mode 100644
index 000000000..246932d81
--- /dev/null
+++ b/passes/techmap/clkbufmap.cc
@@ -0,0 +1,298 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *  Copyright (C) 2019  Marcin Kościelnicki <mwk@0x04.net>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+void split_portname_pair(std::string &port1, std::string &port2)
+{
+	size_t pos = port1.find_first_of(':');
+	if (pos != std::string::npos) {
+		port2 = port1.substr(pos+1);
+		port1 = port1.substr(0, pos);
+	}
+}
+
+struct ClkbufmapPass : public Pass {
+	ClkbufmapPass() : Pass("clkbufmap", "insert global buffers on clock networks") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    clkbufmap [options] [selection]\n");
+		log("\n");
+		log("Inserts global buffers between nets connected to clock inputs and their drivers.\n");
+		log("\n");
+		log("In the absence of any selection, all wires without the 'clkbuf_inhibit'\n");
+		log("attribute will be considered for global buffer insertion.\n");
+		log("Alternatively, to consider all wires without the 'buffer_type' attribute set to\n");
+		log("'none' or 'bufr' one would specify:\n");
+		log("  'w:* a:buffer_type=none a:buffer_type=bufr %%u %%d'\n");
+		log("as the selection.\n");
+		log("\n");
+		log("    -buf <celltype> <portname_out>:<portname_in>\n");
+		log("        Specifies the cell type to use for the global buffers\n");
+		log("        and its port names.  The first port will be connected to\n");
+		log("        the clock network sinks, and the second will be connected\n");
+		log("        to the actual clock source.  This option is required.\n");
+		log("\n");
+		log("    -inpad <celltype> <portname_out>:<portname_in>\n");
+		log("        If specified, a PAD cell of the given type is inserted on\n");
+		log("        clock nets that are also top module's inputs (in addition\n");
+		log("        to the global buffer).\n");
+		log("\n");
+	}
+
+	void module_queue(Design *design, Module *module, std::vector<Module *> &modules_sorted, pool<Module *> &modules_processed) {
+		if (modules_processed.count(module))
+			return;
+		for (auto cell : module->cells()) {
+			Module *submodule = design->module(cell->type);
+			if (!submodule)
+				continue;
+			module_queue(design, submodule, modules_sorted, modules_processed);
+		}
+		modules_sorted.push_back(module);
+		modules_processed.insert(module);
+	}
+
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		log_header(design, "Executing CLKBUFMAP pass (inserting global clock buffers).\n");
+
+		std::string buf_celltype, buf_portname, buf_portname2;
+		std::string inpad_celltype, inpad_portname, inpad_portname2;
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++)
+		{
+			std::string arg = args[argidx];
+			if (arg == "-buf" && argidx+2 < args.size()) {
+				buf_celltype = args[++argidx];
+				buf_portname = args[++argidx];
+				split_portname_pair(buf_portname, buf_portname2);
+				continue;
+			}
+			if (arg == "-inpad" && argidx+2 < args.size()) {
+				inpad_celltype = args[++argidx];
+				inpad_portname = args[++argidx];
+				split_portname_pair(inpad_portname, inpad_portname2);
+				continue;
+			}
+			break;
+		}
+
+		bool select = false;
+		if (argidx < args.size()) {
+			if (args[argidx].compare(0, 1, "-") != 0)
+				select = true;
+			extra_args(args, argidx, design);
+		}
+
+		if (buf_celltype.empty())
+			log_error("The -buf option is required.\n");
+
+		// Cell type, port name, bit index.
+		pool<pair<IdString, pair<IdString, int>>> sink_ports;
+		pool<pair<IdString, pair<IdString, int>>> buf_ports;
+
+		// Process submodules before module using them.
+		std::vector<Module *> modules_sorted;
+		pool<Module *> modules_processed;
+		for (auto module : design->selected_modules())
+			module_queue(design, module, modules_sorted, modules_processed);
+
+		for (auto module : modules_sorted)
+		{
+			if (module->get_blackbox_attribute()) {
+				for (auto port : module->ports) {
+					auto wire = module->wire(port);
+					if (wire->get_bool_attribute("\\clkbuf_driver"))
+						for (int i = 0; i < GetSize(wire); i++)
+							buf_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+					if (wire->get_bool_attribute("\\clkbuf_sink"))
+						for (int i = 0; i < GetSize(wire); i++)
+							sink_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+				}
+				continue;
+			}
+			pool<SigBit> sink_wire_bits;
+			pool<SigBit> buf_wire_bits;
+			pool<SigBit> driven_wire_bits;
+			SigMap sigmap(module);
+			// bit -> (buffer, buffer's input)
+			dict<SigBit, pair<Cell *, Wire *>> buffered_bits;
+
+			// First, collect nets that could use a clock buffer.
+			for (auto cell : module->cells())
+			for (auto port : cell->connections())
+			for (int i = 0; i < port.second.size(); i++)
+				if (sink_ports.count(make_pair(cell->type, make_pair(port.first, i))))
+					sink_wire_bits.insert(sigmap(port.second[i]));
+
+			// Second, collect ones that already have a clock buffer.
+			for (auto cell : module->cells())
+			for (auto port : cell->connections())
+			for (int i = 0; i < port.second.size(); i++)
+				if (buf_ports.count(make_pair(cell->type, make_pair(port.first, i))))
+					buf_wire_bits.insert(sigmap(port.second[i]));
+
+			// Collect all driven bits.
+			for (auto cell : module->cells())
+			for (auto port : cell->connections())
+				if (cell->output(port.first))
+					for (int i = 0; i < port.second.size(); i++)
+						driven_wire_bits.insert(port.second[i]);
+
+			// Insert buffers.
+			std::vector<pair<Wire *, Wire *>> input_queue;
+			// Copy current wire list, as we will be adding new ones during iteration.
+			std::vector<Wire *> wires(module->wires());
+			for (auto wire : wires)
+			{
+				// Should not happen.
+				if (wire->port_input && wire->port_output)
+					continue;
+				bool process_wire = module->selected(wire);
+				if (!select && wire->get_bool_attribute("\\clkbuf_inhibit"))
+					process_wire = false;
+				if (!process_wire) {
+					// This wire is supposed to be bypassed, so make sure we don't buffer it in
+					// some buffer higher up in the hierarchy.
+					if (wire->port_output)
+						for (int i = 0; i < GetSize(wire); i++)
+							buf_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+					continue;
+				}
+
+				pool<int> input_bits;
+
+				for (int i = 0; i < GetSize(wire); i++)
+				{
+					SigBit wire_bit(wire, i);
+					SigBit mapped_wire_bit = sigmap(wire_bit);
+					if (buf_wire_bits.count(mapped_wire_bit)) {
+						// Already buffered downstream.  If this is an output, mark it.
+						if (wire->port_output)
+							buf_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+					} else if (!sink_wire_bits.count(mapped_wire_bit)) {
+						// Nothing to do.
+					} else if (driven_wire_bits.count(wire_bit) || (wire->port_input && module->get_bool_attribute("\\top"))) {
+						// Clock network not yet buffered, driven by one of
+						// our cells or a top-level input -- buffer it.
+
+						log("Inserting %s on %s.%s[%d].\n", buf_celltype.c_str(), log_id(module), log_id(wire), i);
+						RTLIL::Cell *cell = module->addCell(NEW_ID, RTLIL::escape_id(buf_celltype));
+						Wire *iwire = module->addWire(NEW_ID);
+						cell->setPort(RTLIL::escape_id(buf_portname), mapped_wire_bit);
+						cell->setPort(RTLIL::escape_id(buf_portname2), iwire);
+						if (wire->port_input && !inpad_celltype.empty() && module->get_bool_attribute("\\top")) {
+							log("Inserting %s on %s.%s[%d].\n", inpad_celltype.c_str(), log_id(module), log_id(wire), i);
+							RTLIL::Cell *cell2 = module->addCell(NEW_ID, RTLIL::escape_id(inpad_celltype));
+							cell2->setPort(RTLIL::escape_id(inpad_portname), iwire);
+							iwire = module->addWire(NEW_ID);
+							cell2->setPort(RTLIL::escape_id(inpad_portname2), iwire);
+						}
+						buffered_bits[mapped_wire_bit] = make_pair(cell, iwire);
+
+						if (wire->port_input) {
+							input_bits.insert(i);
+						}
+					} else if (wire->port_input) {
+						// A clock input in a submodule -- mark it, let higher level
+						// worry about it.
+						if (wire->port_input)
+							sink_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+					}
+				}
+				if (!input_bits.empty()) {
+					// This is an input port and some buffers were inserted -- we need
+					// to create a new input wire and transfer attributes.
+					Wire *new_wire = module->addWire(NEW_ID, wire);
+
+					for (int i = 0; i < wire->width; i++) {
+						SigBit wire_bit(wire, i);
+						SigBit mapped_wire_bit = sigmap(wire_bit);
+						auto it = buffered_bits.find(mapped_wire_bit);
+						if (it != buffered_bits.end()) {
+
+							module->connect(it->second.second, SigSpec(new_wire, i));
+						} else {
+							module->connect(SigSpec(wire, i), SigSpec(new_wire, i));
+						}
+					}
+					input_queue.push_back(make_pair(wire, new_wire));
+				}
+			}
+
+			// Mark any newly-buffered output ports as such.
+			for (auto wire : module->selected_wires()) {
+				if (wire->port_input || !wire->port_output)
+					continue;
+				for (int i = 0; i < GetSize(wire); i++)
+				{
+					SigBit wire_bit(wire, i);
+					SigBit mapped_wire_bit = sigmap(wire_bit);
+					if (buffered_bits.count(mapped_wire_bit))
+						buf_ports.insert(make_pair(module->name, make_pair(wire->name, i)));
+				}
+			}
+
+			// Reconnect the drivers to buffer inputs.
+			for (auto cell : module->cells())
+			for (auto port : cell->connections()) {
+				if (!cell->output(port.first))
+					continue;
+				SigSpec sig = port.second;
+				bool newsig = false;
+				for (auto &bit : sig) {
+					const auto it = buffered_bits.find(sigmap(bit));
+					if (it == buffered_bits.end())
+						continue;
+					// Avoid substituting buffer's own output pin.
+					if (cell == it->second.first)
+						continue;
+					bit = it->second.second;
+					newsig = true;
+				}
+				if (newsig)
+					cell->setPort(port.first, sig);
+			}
+
+			// This has to be done last, to avoid upsetting sigmap before the port reconnections.
+			for (auto &it : input_queue) {
+				Wire *wire = it.first;
+				Wire *new_wire = it.second;
+				module->swap_names(new_wire, wire);
+				wire->attributes.clear();
+				wire->port_id = 0;
+				wire->port_input = false;
+				wire->port_output = false;
+			}
+
+			module->fixup_ports();
+		}
+	}
+} ClkbufmapPass;
+
+PRIVATE_NAMESPACE_END
diff --git a/passes/techmap/iopadmap.cc b/passes/techmap/iopadmap.cc
index a2551316f..c868b9a87 100644
--- a/passes/techmap/iopadmap.cc
+++ b/passes/techmap/iopadmap.cc
@@ -64,6 +64,11 @@ struct IopadmapPass : public Pass {
 		log("        of the tristate driver and the 2nd portname is the internal output\n");
 		log("        buffering the external signal.\n");
 		log("\n");
+		log("    -ignore <celltype> <portname>[:<portname>]*\n");
+		log("        Skips mapping inputs/outputs that are already connected to given\n");
+		log("        ports of the given cell.  Can be used multiple times.  This is in\n");
+		log("        addition to the cells specified as mapping targets.\n");
+		log("\n");
 		log("    -widthparam <param_name>\n");
 		log("        Use the specified parameter name to set the port width.\n");
 		log("\n");
@@ -88,6 +93,7 @@ struct IopadmapPass : public Pass {
 		std::string toutpad_celltype, toutpad_portname, toutpad_portname2, toutpad_portname3;
 		std::string tinoutpad_celltype, tinoutpad_portname, tinoutpad_portname2, tinoutpad_portname3, tinoutpad_portname4;
 		std::string widthparam, nameparam;
+		pool<pair<IdString, IdString>> ignore;
 		bool flag_bits = false;
 
 		size_t argidx;
@@ -127,6 +133,18 @@ struct IopadmapPass : public Pass {
 				split_portname_pair(tinoutpad_portname3, tinoutpad_portname4);
 				continue;
 			}
+			if (arg == "-ignore" && argidx+2 < args.size()) {
+				std::string ignore_celltype = args[++argidx];
+				std::string ignore_portname = args[++argidx];
+				std::string ignore_portname2;
+				while (!ignore_portname.empty()) {
+					split_portname_pair(ignore_portname, ignore_portname2);
+					ignore.insert(make_pair(RTLIL::escape_id(ignore_celltype), RTLIL::escape_id(ignore_portname)));
+
+					ignore_portname = ignore_portname2;
+				}
+				continue;
+			}
 			if (arg == "-widthparam" && argidx+1 < args.size()) {
 				widthparam = args[++argidx];
 				continue;
@@ -143,6 +161,23 @@ struct IopadmapPass : public Pass {
 		}
 		extra_args(args, argidx, design);
 
+		if (!inpad_portname2.empty())
+			ignore.insert(make_pair(RTLIL::escape_id(inpad_celltype), RTLIL::escape_id(inpad_portname2)));
+		if (!outpad_portname2.empty())
+			ignore.insert(make_pair(RTLIL::escape_id(outpad_celltype), RTLIL::escape_id(outpad_portname2)));
+		if (!inoutpad_portname2.empty())
+			ignore.insert(make_pair(RTLIL::escape_id(inoutpad_celltype), RTLIL::escape_id(inoutpad_portname2)));
+		if (!toutpad_portname3.empty())
+			ignore.insert(make_pair(RTLIL::escape_id(toutpad_celltype), RTLIL::escape_id(toutpad_portname3)));
+		if (!tinoutpad_portname4.empty())
+			ignore.insert(make_pair(RTLIL::escape_id(tinoutpad_celltype), RTLIL::escape_id(tinoutpad_portname4)));
+
+		for (auto module : design->modules())
+			if (module->get_blackbox_attribute())
+				for (auto wire : module->wires())
+					if (wire->get_bool_attribute("\\iopad_external_pin"))
+						ignore.insert(make_pair(module->name, wire->name));
+
 		for (auto module : design->selected_modules())
 		{
 			dict<IdString, pool<int>> skip_wires;
@@ -150,28 +185,11 @@ struct IopadmapPass : public Pass {
 			SigMap sigmap(module);
 
 			for (auto cell : module->cells())
-			{
-				if (cell->type == RTLIL::escape_id(inpad_celltype) && cell->hasPort(RTLIL::escape_id(inpad_portname2)))
-					for (auto bit : sigmap(cell->getPort(RTLIL::escape_id(inpad_portname2))))
+			for (auto port : cell->connections())
+				if (ignore.count(make_pair(cell->type, port.first)))
+					for (auto bit : sigmap(port.second))
 						skip_wire_bits.insert(bit);
 
-				if (cell->type == RTLIL::escape_id(outpad_celltype) && cell->hasPort(RTLIL::escape_id(outpad_portname2)))
-					for (auto bit : sigmap(cell->getPort(RTLIL::escape_id(outpad_portname2))))
-						skip_wire_bits.insert(bit);
-
-				if (cell->type == RTLIL::escape_id(inoutpad_celltype) && cell->hasPort(RTLIL::escape_id(inoutpad_portname2)))
-					for (auto bit : sigmap(cell->getPort(RTLIL::escape_id(inoutpad_portname2))))
-						skip_wire_bits.insert(bit);
-
-				if (cell->type == RTLIL::escape_id(toutpad_celltype) && cell->hasPort(RTLIL::escape_id(toutpad_portname3)))
-					for (auto bit : sigmap(cell->getPort(RTLIL::escape_id(toutpad_portname3))))
-						skip_wire_bits.insert(bit);
-
-				if (cell->type == RTLIL::escape_id(tinoutpad_celltype) && cell->hasPort(RTLIL::escape_id(tinoutpad_portname4)))
-					for (auto bit : sigmap(cell->getPort(RTLIL::escape_id(tinoutpad_portname4))))
-						skip_wire_bits.insert(bit);
-			}
-
 			if (!toutpad_celltype.empty() || !tinoutpad_celltype.empty())
 			{
 				dict<SigBit, pair<IdString, pool<IdString>>> tbuf_bits;
diff --git a/techlibs/xilinx/cells_sim.v b/techlibs/xilinx/cells_sim.v
index 3ad96d7fb..aeef7f885 100644
--- a/techlibs/xilinx/cells_sim.v
+++ b/techlibs/xilinx/cells_sim.v
@@ -29,24 +29,35 @@ module GND(output G);
   assign G = 0;
 endmodule
 
-module IBUF(output O, input I);
+module IBUF(
+    output O,
+    (* iopad_external_pin *)
+    input I);
   parameter IOSTANDARD = "default";
   parameter IBUF_LOW_PWR = 0;
   assign O = I;
 endmodule
 
-module OBUF(output O, input I);
+module OBUF(
+    (* iopad_external_pin *)
+    output O,
+    input I);
   parameter IOSTANDARD = "default";
   parameter DRIVE = 12;
   parameter SLEW = "SLOW";
   assign O = I;
 endmodule
 
-module BUFG(output O, input I);
+module BUFG(
+    (* clkbuf_driver *)
+    output O,
+    input I);
+
   assign O = I;
 endmodule
 
 module BUFGCTRL(
+    (* clkbuf_driver *)
     output O,
     input I0, input I1,
     input S0, input S1,
@@ -72,7 +83,11 @@ assign O = S0_true ? I0_internal : (S1_true ? I1_internal : INIT_OUT);
 
 endmodule
 
-module BUFHCE(output O, input I, input CE);
+module BUFHCE(
+    (* clkbuf_driver *)
+    output O,
+    input I,
+    input CE);
 
 parameter [0:0] INIT_OUT = 1'b0;
 parameter CE_TYPE = "SYNC";
@@ -221,7 +236,7 @@ endmodule
 
 `endif
 
-module FDRE (output reg Q, input C, CE, D, R);
+module FDRE (output reg Q, (* clkbuf_sink *) input C, input CE, D, R);
   parameter [0:0] INIT = 1'b0;
   parameter [0:0] IS_C_INVERTED = 1'b0;
   parameter [0:0] IS_D_INVERTED = 1'b0;
@@ -233,7 +248,7 @@ module FDRE (output reg Q, input C, CE, D, R);
   endcase endgenerate
 endmodule
 
-module FDSE (output reg Q, input C, CE, D, S);
+module FDSE (output reg Q, (* clkbuf_sink *) input C, input CE, D, S);
   parameter [0:0] INIT = 1'b1;
   parameter [0:0] IS_C_INVERTED = 1'b0;
   parameter [0:0] IS_D_INVERTED = 1'b0;
@@ -245,7 +260,7 @@ module FDSE (output reg Q, input C, CE, D, S);
   endcase endgenerate
 endmodule
 
-module FDCE (output reg Q, input C, CE, D, CLR);
+module FDCE (output reg Q, (* clkbuf_sink *) input C, input CE, D, CLR);
   parameter [0:0] INIT = 1'b0;
   parameter [0:0] IS_C_INVERTED = 1'b0;
   parameter [0:0] IS_D_INVERTED = 1'b0;
@@ -259,7 +274,7 @@ module FDCE (output reg Q, input C, CE, D, CLR);
   endcase endgenerate
 endmodule
 
-module FDPE (output reg Q, input C, CE, D, PRE);
+module FDPE (output reg Q, (* clkbuf_sink *) input C, input CE, D, PRE);
   parameter [0:0] INIT = 1'b1;
   parameter [0:0] IS_C_INVERTED = 1'b0;
   parameter [0:0] IS_D_INVERTED = 1'b0;
@@ -273,25 +288,25 @@ module FDPE (output reg Q, input C, CE, D, PRE);
   endcase endgenerate
 endmodule
 
-module FDRE_1 (output reg Q, input C, CE, D, R);
+module FDRE_1 (output reg Q, (* clkbuf_sink *) input C, input CE, D, R);
   parameter [0:0] INIT = 1'b0;
   initial Q <= INIT;
   always @(negedge C) if (R) Q <= 1'b0; else if(CE) Q <= D;
 endmodule
 
-module FDSE_1 (output reg Q, input C, CE, D, S);
+module FDSE_1 (output reg Q, (* clkbuf_sink *) input C, input CE, D, S);
   parameter [0:0] INIT = 1'b1;
   initial Q <= INIT;
   always @(negedge C) if (S) Q <= 1'b1; else if(CE) Q <= D;
 endmodule
 
-module FDCE_1 (output reg Q, input C, CE, D, CLR);
+module FDCE_1 (output reg Q, (* clkbuf_sink *) input C, input CE, D, CLR);
   parameter [0:0] INIT = 1'b0;
   initial Q <= INIT;
   always @(negedge C, posedge CLR) if (CLR) Q <= 1'b0; else if (CE) Q <= D;
 endmodule
 
-module FDPE_1 (output reg Q, input C, CE, D, PRE);
+module FDPE_1 (output reg Q, (* clkbuf_sink *) input C, input CE, D, PRE);
   parameter [0:0] INIT = 1'b1;
   initial Q <= INIT;
   always @(negedge C, posedge PRE) if (PRE) Q <= 1'b1; else if (CE) Q <= D;
@@ -302,6 +317,7 @@ module RAM32X1D (
   output DPO, SPO,
   (* abc_scc_break *)
   input  D,
+  (* clkbuf_sink *)
   input  WCLK,
   (* abc_scc_break *)
   input  WE,
@@ -324,6 +340,7 @@ module RAM64X1D (
   output DPO, SPO,
   (* abc_scc_break *)
   input  D,
+  (* clkbuf_sink *)
   input  WCLK,
   (* abc_scc_break *)
   input  WE,
@@ -346,6 +363,7 @@ module RAM128X1D (
   output       DPO, SPO,
   (* abc_scc_break *)
   input        D,
+  (* clkbuf_sink *)
   input        WCLK,
   (* abc_scc_break *)
   input        WE,
@@ -362,7 +380,9 @@ endmodule
 
 module SRL16E (
   output Q,
-  input A0, A1, A2, A3, CE, CLK, D
+  (* clkbuf_sink *)
+  input CLK,
+  input A0, A1, A2, A3, CE, D
 );
   parameter [15:0] INIT = 16'h0000;
   parameter [0:0] IS_CLK_INVERTED = 1'b0;
@@ -382,7 +402,9 @@ module SRLC32E (
   output Q,
   output Q31,
   input [4:0] A,
-  input CE, CLK, D
+  (* clkbuf_sink *)
+  input CLK,
+  input CE, D
 );
   parameter [31:0] INIT = 32'h00000000;
   parameter [0:0] IS_CLK_INVERTED = 1'b0;
diff --git a/techlibs/xilinx/cells_xtra.py b/techlibs/xilinx/cells_xtra.py
new file mode 100644
index 000000000..dd4e300ae
--- /dev/null
+++ b/techlibs/xilinx/cells_xtra.py
@@ -0,0 +1,257 @@
+#!/usr/bin/env python3
+
+from argparse import ArgumentParser
+from io import StringIO
+from enum import Enum, auto
+import os.path
+import sys
+
+
+class Cell:
+    def __init__(self, name, keep=False, port_attrs={}):
+        self.name = name
+        self.keep = keep
+        self.port_attrs = port_attrs
+
+
+CELLS = [
+    # Design elements types listed in Xilinx UG953
+    Cell('BSCANE2', keep=True),
+    # Cell('BUFG', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFGCE', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFGCE_1', port_attrs={'O': ['clkbuf_driver']}),
+    #Cell('BUFGCTRL', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFGMUX', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFGMUX_1', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFGMUX_CTRL', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFH', port_attrs={'O': ['clkbuf_driver']}),
+    #Cell('BUFHCE', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFIO', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFMR', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFMRCE', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('BUFR', port_attrs={'O': ['clkbuf_driver']}),
+    Cell('CAPTUREE2', keep=True),
+    # Cell('CARRY4'),
+    Cell('CFGLUT5', port_attrs={'CLK': ['clkbuf_sink']}),
+    Cell('DCIRESET', keep=True),
+    Cell('DNA_PORT'),
+    Cell('DSP48E1', port_attrs={'CLK': ['clkbuf_sink']}),
+    Cell('EFUSE_USR'),
+    # Cell('FDCE'),
+    # Cell('FDPE'),
+    # Cell('FDRE'),
+    # Cell('FDSE'),
+    Cell('FIFO18E1', port_attrs={'RDCLK': ['clkbuf_sink'], 'WRCLK': ['clkbuf_sink']}),
+    Cell('FIFO36E1', port_attrs={'RDCLK': ['clkbuf_sink'], 'WRCLK': ['clkbuf_sink']}),
+    Cell('FRAME_ECCE2'),
+    Cell('GTHE2_CHANNEL'),
+    Cell('GTHE2_COMMON'),
+    Cell('GTPE2_CHANNEL'),
+    Cell('GTPE2_COMMON'),
+    Cell('GTXE2_CHANNEL'),
+    Cell('GTXE2_COMMON'),
+    # Cell('IBUF', port_attrs={'I': ['iopad_external_pin']}),
+    Cell('IBUF_IBUFDISABLE', port_attrs={'I': ['iopad_external_pin']}),
+    Cell('IBUF_INTERMDISABLE', port_attrs={'I': ['iopad_external_pin']}),
+    Cell('IBUFDS', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_DIFF_OUT', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_DIFF_OUT_IBUFDISABLE', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_DIFF_OUT_INTERMDISABLE', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_GTE2', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_IBUFDISABLE', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFDS_INTERMDISABLE', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFG', port_attrs={'I': ['iopad_external_pin']}),
+    Cell('IBUFGDS', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('IBUFGDS_DIFF_OUT', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
+    Cell('ICAPE2', keep=True),
+    Cell('IDDR', port_attrs={'C': ['clkbuf_sink']}),
+    Cell('IDDR_2CLK', port_attrs={'C': ['clkbuf_sink'], 'CB': ['clkbuf_sink']}),
+    Cell('IDELAYCTRL', keep=True, port_attrs={'REFCLK': ['clkbuf_sink']}),
+    Cell('IDELAYE2', port_attrs={'C': ['clkbuf_sink']}),
+    Cell('IN_FIFO', port_attrs={'RDCLK': ['clkbuf_sink'], 'WRCLK': ['clkbuf_sink']}),
+    Cell('IOBUF', port_attrs={'IO': ['iopad_external_pin']}),
+    Cell('IOBUF_DCIEN', port_attrs={'IO': ['iopad_external_pin']}),
+    Cell('IOBUF_INTERMDISABLE', port_attrs={'IO': ['iopad_external_pin']}),
+    Cell('IOBUFDS', port_attrs={'IO': ['iopad_external_pin']}),
+    Cell('IOBUFDS_DCIEN', port_attrs={'IO': ['iopad_external_pin'], 'IOB': ['iopad_external_pin']}),
+    Cell('IOBUFDS_DIFF_OUT', port_attrs={'IO': ['iopad_external_pin'], 'IOB': ['iopad_external_pin']}),
+    Cell('IOBUFDS_DIFF_OUT_DCIEN', port_attrs={'IO': ['iopad_external_pin'], 'IOB': ['iopad_external_pin']}),
+    Cell('IOBUFDS_DIFF_OUT_INTERMDISABLE', port_attrs={'IO': ['iopad_external_pin'], 'IOB': ['iopad_external_pin']}),
+    Cell('ISERDESE2', port_attrs={
+        'CLK': ['clkbuf_sink'],
+        'CLKB': ['clkbuf_sink'],
+        'OCLK': ['clkbuf_sink'],
+        'OCLKB': ['clkbuf_sink'],
+        'CLKDIV': ['clkbuf_sink'],
+        'CLKDIVP': ['clkbuf_sink'],
+    }),
+    Cell('KEEPER'),
+    Cell('LDCE'),
+    Cell('LDPE'),
+    # Cell('LUT1'),
+    # Cell('LUT2'),
+    # Cell('LUT3'),
+    # Cell('LUT4'),
+    # Cell('LUT5'),
+    # Cell('LUT6'),
+    #Cell('LUT6_2'),
+    Cell('MMCME2_ADV'),
+    Cell('MMCME2_BASE'),
+    # Cell('MUXF7'),
+    # Cell('MUXF8'),
+    # Cell('OBUF', port_attrs={'O': ['iopad_external_pin']}),
+    Cell('OBUFDS', port_attrs={'O': ['iopad_external_pin'], 'OB': ['iopad_external_pin']}),
+    Cell('OBUFT', port_attrs={'O': ['iopad_external_pin']}),
+    Cell('OBUFTDS', port_attrs={'O': ['iopad_external_pin'], 'OB': ['iopad_external_pin']}),
+    Cell('ODDR', port_attrs={'C': ['clkbuf_sink']}),
+    Cell('ODELAYE2', port_attrs={'C': ['clkbuf_sink']}),
+    Cell('OSERDESE2', port_attrs={'CLK': ['clkbuf_sink'], 'CLKDIV': ['clkbuf_sink']}),
+    Cell('OUT_FIFO', port_attrs={'RDCLK': ['clkbuf_sink'], 'WRCLK': ['clkbuf_sink']}),
+    Cell('PHASER_IN'),
+    Cell('PHASER_IN_PHY'),
+    Cell('PHASER_OUT'),
+    Cell('PHASER_OUT_PHY'),
+    Cell('PHASER_REF'),
+    Cell('PHY_CONTROL'),
+    Cell('PLLE2_ADV'),
+    Cell('PLLE2_BASE'),
+    Cell('PS7', keep=True),
+    Cell('PULLDOWN'),
+    Cell('PULLUP'),
+    #Cell('RAM128X1D', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM128X1S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM256X1S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM32M', port_attrs={'WCLK': ['clkbuf_sink']}),
+    #Cell('RAM32X1D', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM32X1S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM32X1S_1', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM32X2S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM64M', port_attrs={'WCLK': ['clkbuf_sink']}),
+    #Cell('RAM64X1D', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM64X1S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM64X1S_1', port_attrs={'WCLK': ['clkbuf_sink']}),
+    Cell('RAM64X2S', port_attrs={'WCLK': ['clkbuf_sink']}),
+    # Cell('RAMB18E1', port_attrs={'CLKARDCLK': ['clkbuf_sink'], 'CLKBWRCLK': ['clkbuf_sink']}),
+    # Cell('RAMB36E1', port_attrs={'CLKARDCLK': ['clkbuf_sink'], 'CLKBWRCLK': ['clkbuf_sink']}),
+    Cell('ROM128X1'),
+    Cell('ROM256X1'),
+    Cell('ROM32X1'),
+    Cell('ROM64X1'),
+    #Cell('SRL16E', port_attrs={'CLK': ['clkbuf_sink']}),
+    #Cell('SRLC32E', port_attrs={'CLK': ['clkbuf_sink']}),
+    Cell('STARTUPE2', keep=True),
+    Cell('USR_ACCESSE2'),
+    Cell('XADC'),
+]
+
+class State(Enum):
+    OUTSIDE = auto()
+    IN_MODULE = auto()
+    IN_OTHER_MODULE = auto()
+    IN_FUNCTION = auto()
+    IN_TASK = auto()
+
+def xtract_cell_decl(cell, dirs, outf):
+    for dir in dirs:
+        fname = os.path.join(dir, cell.name + '.v')
+        try:
+            with open(fname) as f:
+                state = State.OUTSIDE
+                found = False
+                # Probably the most horrible Verilog "parser" ever written.
+                for l in f:
+                    l = l.partition('//')[0]
+                    l = l.strip()
+                    if l == 'module {}'.format(cell.name) or l.startswith('module {} '.format(cell.name)):
+                        if found:
+                            print('Multiple modules in {}.'.format(fname))
+                            sys.exit(1)
+                        elif state != State.OUTSIDE:
+                            print('Nested modules in {}.'.format(fname))
+                            sys.exit(1)
+                        found = True
+                        state = State.IN_MODULE
+                        if cell.keep:
+                            outf.write('(* keep *)\n')
+                        outf.write('module {} (...);\n'.format(cell.name))
+                    elif l.startswith('module '):
+                        if state != State.OUTSIDE:
+                            print('Nested modules in {}.'.format(fname))
+                            sys.exit(1)
+                        state = State.IN_OTHER_MODULE
+                    elif l.startswith('task '):
+                        if state == State.IN_MODULE:
+                            state = State.IN_TASK
+                    elif l.startswith('function '):
+                        if state == State.IN_MODULE:
+                            state = State.IN_FUNCTION
+                    elif l == 'endtask':
+                        if state == State.IN_TASK:
+                            state = State.IN_MODULE
+                    elif l == 'endfunction':
+                        if state == State.IN_FUNCTION:
+                            state = State.IN_MODULE
+                    elif l == 'endmodule':
+                        if state == State.IN_MODULE:
+                            outf.write(l + '\n')
+                            outf.write('\n')
+                        elif state != State.IN_OTHER_MODULE:
+                            print('endmodule in weird place in {}.'.format(cell.name, fname))
+                            sys.exit(1)
+                        state = State.OUTSIDE
+                    elif l.startswith(('input ', 'output ', 'inout ')) and state == State.IN_MODULE:
+                        if l.endswith((';', ',')):
+                            l = l[:-1]
+                        if ';' in l:
+                            print('Weird port line in {} [{}].'.format(fname, l))
+                            sys.exit(1)
+                        kind, _, ports = l.partition(' ')
+                        for port in ports.split(','):
+                            port = port.strip()
+                            for attr in cell.port_attrs.get(port, []):
+                                outf.write('    (* {} *)\n'.format(attr))
+                            outf.write('    {} {};\n'.format(kind, port))
+                    elif l.startswith('parameter ') and state == State.IN_MODULE:
+                        if 'UNPLACED' in l:
+                            continue
+                        if l.endswith((';', ',')):
+                            l = l[:-1]
+                        while '  ' in l:
+                            l = l.replace('  ', ' ')
+                        if ';' in l:
+                            print('Weird parameter line in {} [{}].'.format(fname, l))
+                            sys.exit(1)
+                        outf.write('    {};\n'.format(l))
+                if state != State.OUTSIDE:
+                    print('endmodule not found in {}.'.format(fname))
+                    sys.exit(1)
+                if not found:
+                    print('Cannot find module {} in {}.'.format(cell.name, fname))
+                    sys.exit(1)
+            return
+        except FileNotFoundError:
+            continue
+    print('Cannot find {}.'.format(cell.name))
+    sys.exit(1)
+
+if __name__ == '__main__':
+    parser = ArgumentParser(description='Extract Xilinx blackbox cell definitions from Vivado.')
+    parser.add_argument('vivado_dir', nargs='?', default='/opt/Xilinx/Vivado/2018.1')
+    args = parser.parse_args()
+
+    dirs = [
+        os.path.join(args.vivado_dir, 'data/verilog/src/xeclib'),
+        os.path.join(args.vivado_dir, 'data/verilog/src/retarget'),
+    ]
+    for dir in dirs:
+        if not os.path.isdir(dir):
+            print('{} is not a directory'.format(dir))
+
+    out = StringIO()
+    for cell in CELLS:
+        xtract_cell_decl(cell, dirs, out)
+
+    with open('cells_xtra.v', 'w') as f:
+        f.write('// Created by cells_xtra.py from Xilinx models\n')
+        f.write('\n')
+        f.write(out.getvalue())
diff --git a/techlibs/xilinx/cells_xtra.sh b/techlibs/xilinx/cells_xtra.sh
deleted file mode 100644
index 53b528820..000000000
--- a/techlibs/xilinx/cells_xtra.sh
+++ /dev/null
@@ -1,147 +0,0 @@
-#!/bin/bash
-
-set -e
-libdir="/opt/Xilinx/Vivado/2018.1/data/verilog/src"
-
-function xtract_cell_decl()
-{
-	for dir in $libdir/xeclib $libdir/retarget; do
-		[ -f $dir/$1.v ] || continue
-		[ -z "$2" ] || echo $2
-		egrep '^\s*((end)?module|parameter|input|inout|output|(end)?function|(end)?task)' $dir/$1.v |
-			sed -re '/UNPLACED/ d; /^\s*function/,/endfunction/ d; /^\s*task/,/endtask/ d;
-			         s,//.*,,; s/#?\(.*/(...);/; s/^(input|output|parameter)/ \1/;
-			         s/\s+$//; s/,$/;/; /input|output|parameter/ s/[^;]$/&;/; s/\s+/ /g;
-				 s/^ ((end)?module)/\1/; s/^ /    /; /module.*_bb/,/endmodule/ d;'
-		echo; return
-	done
-	echo "Can't find $1."
-	exit 1
-}
-
-{
-	echo "// Created by cells_xtra.sh from Xilinx models"
-	echo
-
-	# Design elements types listed in Xilinx UG953
-	xtract_cell_decl BSCANE2
-	# xtract_cell_decl BUFG
-	xtract_cell_decl BUFGCE
-	xtract_cell_decl BUFGCE_1
-	#xtract_cell_decl BUFGCTRL
-	xtract_cell_decl BUFGMUX
-	xtract_cell_decl BUFGMUX_1
-	xtract_cell_decl BUFGMUX_CTRL
-	xtract_cell_decl BUFH
-	#xtract_cell_decl BUFHCE
-	xtract_cell_decl BUFIO
-	xtract_cell_decl BUFMR
-	xtract_cell_decl BUFMRCE
-	xtract_cell_decl BUFR
-	xtract_cell_decl CAPTUREE2 "(* keep *)"
-	# xtract_cell_decl CARRY4
-	xtract_cell_decl CFGLUT5
-	xtract_cell_decl DCIRESET "(* keep *)"
-	xtract_cell_decl DNA_PORT
-	xtract_cell_decl DSP48E1
-	xtract_cell_decl EFUSE_USR
-	# xtract_cell_decl FDCE
-	# xtract_cell_decl FDPE
-	# xtract_cell_decl FDRE
-	# xtract_cell_decl FDSE
-	xtract_cell_decl FIFO18E1
-	xtract_cell_decl FIFO36E1
-	xtract_cell_decl FRAME_ECCE2
-	xtract_cell_decl GTHE2_CHANNEL
-	xtract_cell_decl GTHE2_COMMON
-	xtract_cell_decl GTPE2_CHANNEL
-	xtract_cell_decl GTPE2_COMMON
-	xtract_cell_decl GTXE2_CHANNEL
-	xtract_cell_decl GTXE2_COMMON
-	# xtract_cell_decl IBUF
-	xtract_cell_decl IBUF_IBUFDISABLE
-	xtract_cell_decl IBUF_INTERMDISABLE
-	xtract_cell_decl IBUFDS
-	xtract_cell_decl IBUFDS_DIFF_OUT
-	xtract_cell_decl IBUFDS_DIFF_OUT_IBUFDISABLE
-	xtract_cell_decl IBUFDS_DIFF_OUT_INTERMDISABLE
-	xtract_cell_decl IBUFDS_GTE2
-	xtract_cell_decl IBUFDS_IBUFDISABLE
-	xtract_cell_decl IBUFDS_INTERMDISABLE
-	xtract_cell_decl ICAPE2 "(* keep *)"
-	xtract_cell_decl IDDR
-	xtract_cell_decl IDDR_2CLK
-	xtract_cell_decl IDELAYCTRL "(* keep *)"
-	xtract_cell_decl IDELAYE2
-	xtract_cell_decl IN_FIFO
-	xtract_cell_decl IOBUF
-	xtract_cell_decl IOBUF_DCIEN
-	xtract_cell_decl IOBUF_INTERMDISABLE
-	xtract_cell_decl IOBUFDS
-	xtract_cell_decl IOBUFDS_DCIEN
-	xtract_cell_decl IOBUFDS_DIFF_OUT
-	xtract_cell_decl IOBUFDS_DIFF_OUT_DCIEN
-	xtract_cell_decl IOBUFDS_DIFF_OUT_INTERMDISABLE
-	xtract_cell_decl ISERDESE2
-	xtract_cell_decl KEEPER
-	xtract_cell_decl LDCE
-	xtract_cell_decl LDPE
-	# xtract_cell_decl LUT1
-	# xtract_cell_decl LUT2
-	# xtract_cell_decl LUT3
-	# xtract_cell_decl LUT4
-	# xtract_cell_decl LUT5
-	# xtract_cell_decl LUT6
-	#xtract_cell_decl LUT6_2
-	xtract_cell_decl MMCME2_ADV
-	xtract_cell_decl MMCME2_BASE
-	# xtract_cell_decl MUXF7
-	# xtract_cell_decl MUXF8
-	# xtract_cell_decl OBUF
-	xtract_cell_decl OBUFDS
-	xtract_cell_decl OBUFT
-	xtract_cell_decl OBUFTDS
-	xtract_cell_decl ODDR
-	xtract_cell_decl ODELAYE2
-	xtract_cell_decl OSERDESE2
-	xtract_cell_decl OUT_FIFO
-	xtract_cell_decl PHASER_IN
-	xtract_cell_decl PHASER_IN_PHY
-	xtract_cell_decl PHASER_OUT
-	xtract_cell_decl PHASER_OUT_PHY
-	xtract_cell_decl PHASER_REF
-	xtract_cell_decl PHY_CONTROL
-	xtract_cell_decl PLLE2_ADV
-	xtract_cell_decl PLLE2_BASE
-	xtract_cell_decl PS7 "(* keep *)"
-	xtract_cell_decl PULLDOWN
-	xtract_cell_decl PULLUP
-	#xtract_cell_decl RAM128X1D
-	xtract_cell_decl RAM128X1S
-	xtract_cell_decl RAM256X1S
-	xtract_cell_decl RAM32M
-	#xtract_cell_decl RAM32X1D
-	xtract_cell_decl RAM32X1S
-	xtract_cell_decl RAM32X1S_1
-	xtract_cell_decl RAM32X2S
-	xtract_cell_decl RAM64M
-	#xtract_cell_decl RAM64X1D
-	xtract_cell_decl RAM64X1S
-	xtract_cell_decl RAM64X1S_1
-	xtract_cell_decl RAM64X2S
-	# xtract_cell_decl RAMB18E1
-	# xtract_cell_decl RAMB36E1
-	xtract_cell_decl ROM128X1
-	xtract_cell_decl ROM256X1
-	xtract_cell_decl ROM32X1
-	xtract_cell_decl ROM64X1
-	#xtract_cell_decl SRL16E
-	#xtract_cell_decl SRLC32E
-	xtract_cell_decl STARTUPE2 "(* keep *)"
-	xtract_cell_decl USR_ACCESSE2
-	xtract_cell_decl XADC
-} > cells_xtra.new
-
-mv cells_xtra.new cells_xtra.v
-exit 0
-
diff --git a/techlibs/xilinx/cells_xtra.v b/techlibs/xilinx/cells_xtra.v
index 15fa1b63a..a6669b872 100644
--- a/techlibs/xilinx/cells_xtra.v
+++ b/techlibs/xilinx/cells_xtra.v
@@ -1,5 +1,6 @@
-// Created by cells_xtra.sh from Xilinx models
+// Created by cells_xtra.py from Xilinx models
 
+(* keep *)
 module BSCANE2 (...);
     parameter DISABLE_JTAG = "FALSE";
     parameter integer JTAG_CHAIN = 1;
@@ -20,29 +21,39 @@ module BUFGCE (...);
     parameter CE_TYPE = "SYNC";
     parameter [0:0] IS_CE_INVERTED = 1'b0;
     parameter [0:0] IS_I_INVERTED = 1'b0;
+    (* clkbuf_driver *)
     output O;
     input CE;
     input I;
 endmodule
 
 module BUFGCE_1 (...);
+    (* clkbuf_driver *)
     output O;
-    input CE, I;
+    input CE;
+    input I;
 endmodule
 
 module BUFGMUX (...);
     parameter CLK_SEL_TYPE = "SYNC";
+    (* clkbuf_driver *)
     output O;
-    input I0, I1, S;
+    input I0;
+    input I1;
+    input S;
 endmodule
 
 module BUFGMUX_1 (...);
     parameter CLK_SEL_TYPE = "SYNC";
+    (* clkbuf_driver *)
     output O;
-    input I0, I1, S;
+    input I0;
+    input I1;
+    input S;
 endmodule
 
 module BUFGMUX_CTRL (...);
+    (* clkbuf_driver *)
     output O;
     input I0;
     input I1;
@@ -50,16 +61,19 @@ module BUFGMUX_CTRL (...);
 endmodule
 
 module BUFH (...);
+    (* clkbuf_driver *)
     output O;
     input I;
 endmodule
 
 module BUFIO (...);
+    (* clkbuf_driver *)
     output O;
     input I;
 endmodule
 
 module BUFMR (...);
+    (* clkbuf_driver *)
     output O;
     input I;
 endmodule
@@ -68,12 +82,14 @@ module BUFMRCE (...);
     parameter CE_TYPE = "SYNC";
     parameter integer INIT_OUT = 0;
     parameter [0:0] IS_CE_INVERTED = 1'b0;
+    (* clkbuf_driver *)
     output O;
     input CE;
     input I;
 endmodule
 
 module BUFR (...);
+    (* clkbuf_driver *)
     output O;
     input CE;
     input CLR;
@@ -95,8 +111,15 @@ module CFGLUT5 (...);
     output CDO;
     output O5;
     output O6;
-    input I4, I3, I2, I1, I0;
-    input CDI, CE, CLK;
+    input I4;
+    input I3;
+    input I2;
+    input I1;
+    input I0;
+    input CDI;
+    input CE;
+    (* clkbuf_sink *)
+    input CLK;
 endmodule
 
 (* keep *)
@@ -108,7 +131,10 @@ endmodule
 module DNA_PORT (...);
     parameter [56:0] SIM_DNA_VALUE = 57'h0;
     output DOUT;
-    input CLK, DIN, READ, SHIFT;
+    input CLK;
+    input DIN;
+    input READ;
+    input SHIFT;
 endmodule
 
 module DSP48E1 (...);
@@ -175,6 +201,7 @@ module DSP48E1 (...);
     input CEINMODE;
     input CEM;
     input CEP;
+    (* clkbuf_sink *)
     input CLK;
     input [24:0] D;
     input [4:0] INMODE;
@@ -227,11 +254,13 @@ module FIFO18E1 (...);
     output WRERR;
     input [31:0] DI;
     input [3:0] DIP;
+    (* clkbuf_sink *)
     input RDCLK;
     input RDEN;
     input REGCE;
     input RST;
     input RSTREG;
+    (* clkbuf_sink *)
     input WRCLK;
     input WREN;
 endmodule
@@ -272,11 +301,13 @@ module FIFO36E1 (...);
     input [7:0] DIP;
     input INJECTDBITERR;
     input INJECTSBITERR;
+    (* clkbuf_sink *)
     input RDCLK;
     input RDEN;
     input REGCE;
     input RST;
     input RSTREG;
+    (* clkbuf_sink *)
     input WRCLK;
     input WREN;
 endmodule
@@ -1969,6 +2000,7 @@ module IBUF_IBUFDISABLE (...);
     parameter SIM_DEVICE = "7SERIES";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     input I;
     input IBUFDISABLE;
 endmodule
@@ -1979,6 +2011,7 @@ module IBUF_INTERMDISABLE (...);
     parameter SIM_DEVICE = "7SERIES";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     input I;
     input IBUFDISABLE;
     input INTERMDISABLE;
@@ -1993,7 +2026,10 @@ module IBUFDS (...);
     parameter IFD_DELAY_VALUE = "AUTO";
     parameter IOSTANDARD = "DEFAULT";
     output O;
-    input I, IB;
+    (* iopad_external_pin *)
+    input I;
+    (* iopad_external_pin *)
+    input IB;
 endmodule
 
 module IBUFDS_DIFF_OUT (...);
@@ -2001,8 +2037,12 @@ module IBUFDS_DIFF_OUT (...);
     parameter DQS_BIAS = "FALSE";
     parameter IBUF_LOW_PWR = "TRUE";
     parameter IOSTANDARD = "DEFAULT";
-    output O, OB;
-    input I, IB;
+    output O;
+    output OB;
+    (* iopad_external_pin *)
+    input I;
+    (* iopad_external_pin *)
+    input IB;
 endmodule
 
 module IBUFDS_DIFF_OUT_IBUFDISABLE (...);
@@ -2014,7 +2054,9 @@ module IBUFDS_DIFF_OUT_IBUFDISABLE (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    (* iopad_external_pin *)
     input I;
+    (* iopad_external_pin *)
     input IB;
     input IBUFDISABLE;
 endmodule
@@ -2028,7 +2070,9 @@ module IBUFDS_DIFF_OUT_INTERMDISABLE (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    (* iopad_external_pin *)
     input I;
+    (* iopad_external_pin *)
     input IB;
     input IBUFDISABLE;
     input INTERMDISABLE;
@@ -2041,7 +2085,9 @@ module IBUFDS_GTE2 (...);
     output O;
     output ODIV2;
     input CEB;
+    (* iopad_external_pin *)
     input I;
+    (* iopad_external_pin *)
     input IB;
 endmodule
 
@@ -2053,7 +2099,9 @@ module IBUFDS_IBUFDISABLE (...);
     parameter SIM_DEVICE = "7SERIES";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     input I;
+    (* iopad_external_pin *)
     input IB;
     input IBUFDISABLE;
 endmodule
@@ -2066,12 +2114,50 @@ module IBUFDS_INTERMDISABLE (...);
     parameter SIM_DEVICE = "7SERIES";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     input I;
+    (* iopad_external_pin *)
     input IB;
     input IBUFDISABLE;
     input INTERMDISABLE;
 endmodule
 
+module IBUFG (...);
+    parameter CAPACITANCE = "DONT_CARE";
+    parameter IBUF_DELAY_VALUE = "0";
+    parameter IBUF_LOW_PWR = "TRUE";
+    parameter IOSTANDARD = "DEFAULT";
+    output O;
+    (* iopad_external_pin *)
+    input I;
+endmodule
+
+module IBUFGDS (...);
+    parameter CAPACITANCE = "DONT_CARE";
+    parameter DIFF_TERM = "FALSE";
+    parameter IBUF_DELAY_VALUE = "0";
+    parameter IBUF_LOW_PWR = "TRUE";
+    parameter IOSTANDARD = "DEFAULT";
+    output O;
+    (* iopad_external_pin *)
+    input I;
+    (* iopad_external_pin *)
+    input IB;
+endmodule
+
+module IBUFGDS_DIFF_OUT (...);
+    parameter DIFF_TERM = "FALSE";
+    parameter DQS_BIAS = "FALSE";
+    parameter IBUF_LOW_PWR = "TRUE";
+    parameter IOSTANDARD = "DEFAULT";
+    output O;
+    output OB;
+    (* iopad_external_pin *)
+    input I;
+    (* iopad_external_pin *)
+    input IB;
+endmodule
+
 (* keep *)
 module ICAPE2 (...);
     parameter [31:0] DEVICE_ID = 32'h04244093;
@@ -2095,6 +2181,7 @@ module IDDR (...);
     parameter XON = "TRUE";
     output Q1;
     output Q2;
+    (* clkbuf_sink *)
     input C;
     input CE;
     input D;
@@ -2112,7 +2199,9 @@ module IDDR_2CLK (...);
     parameter SRTYPE = "SYNC";
     output Q1;
     output Q2;
+    (* clkbuf_sink *)
     input C;
+    (* clkbuf_sink *)
     input CB;
     input CE;
     input D;
@@ -2124,6 +2213,7 @@ endmodule
 module IDELAYCTRL (...);
     parameter SIM_DEVICE = "7SERIES";
     output RDY;
+    (* clkbuf_sink *)
     input REFCLK;
     input RST;
 endmodule
@@ -2143,6 +2233,7 @@ module IDELAYE2 (...);
     parameter integer SIM_DELAY_D = 0;
     output [4:0] CNTVALUEOUT;
     output DATAOUT;
+    (* clkbuf_sink *)
     input C;
     input CE;
     input CINVCTRL;
@@ -2174,9 +2265,11 @@ module IN_FIFO (...);
     output [7:0] Q7;
     output [7:0] Q8;
     output [7:0] Q9;
+    (* clkbuf_sink *)
     input RDCLK;
     input RDEN;
     input RESET;
+    (* clkbuf_sink *)
     input WRCLK;
     input WREN;
     input [3:0] D0;
@@ -2197,8 +2290,10 @@ module IOBUF (...);
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
     output O;
+    (* iopad_external_pin *)
     inout IO;
-    input I, T;
+    input I;
+    input T;
 endmodule
 
 module IOBUF_DCIEN (...);
@@ -2209,6 +2304,7 @@ module IOBUF_DCIEN (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     inout IO;
     input DCITERMDISABLE;
     input I;
@@ -2224,6 +2320,7 @@ module IOBUF_INTERMDISABLE (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     inout IO;
     input I;
     input IBUFDISABLE;
@@ -2238,8 +2335,11 @@ module IOBUFDS (...);
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
     output O;
-    inout IO, IOB;
-    input I, T;
+    (* iopad_external_pin *)
+    inout IO;
+    inout IOB;
+    input I;
+    input T;
 endmodule
 
 module IOBUFDS_DCIEN (...);
@@ -2251,7 +2351,9 @@ module IOBUFDS_DCIEN (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    (* iopad_external_pin *)
     inout IO;
+    (* iopad_external_pin *)
     inout IOB;
     input DCITERMDISABLE;
     input I;
@@ -2266,7 +2368,9 @@ module IOBUFDS_DIFF_OUT (...);
     parameter IOSTANDARD = "DEFAULT";
     output O;
     output OB;
+    (* iopad_external_pin *)
     inout IO;
+    (* iopad_external_pin *)
     inout IOB;
     input I;
     input TM;
@@ -2282,7 +2386,9 @@ module IOBUFDS_DIFF_OUT_DCIEN (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    (* iopad_external_pin *)
     inout IO;
+    (* iopad_external_pin *)
     inout IOB;
     input DCITERMDISABLE;
     input I;
@@ -2300,7 +2406,9 @@ module IOBUFDS_DIFF_OUT_INTERMDISABLE (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    (* iopad_external_pin *)
     inout IO;
+    (* iopad_external_pin *)
     inout IOB;
     input I;
     input IBUFDISABLE;
@@ -2348,15 +2456,21 @@ module ISERDESE2 (...);
     input BITSLIP;
     input CE1;
     input CE2;
+    (* clkbuf_sink *)
     input CLK;
+    (* clkbuf_sink *)
     input CLKB;
+    (* clkbuf_sink *)
     input CLKDIV;
+    (* clkbuf_sink *)
     input CLKDIVP;
     input D;
     input DDLY;
     input DYNCLKDIVSEL;
     input DYNCLKSEL;
+    (* clkbuf_sink *)
     input OCLK;
+    (* clkbuf_sink *)
     input OCLKB;
     input OFB;
     input RST;
@@ -2375,7 +2489,10 @@ module LDCE (...);
     parameter MSGON = "TRUE";
     parameter XON = "TRUE";
     output Q;
-    input CLR, D, G, GE;
+    input CLR;
+    input D;
+    input G;
+    input GE;
 endmodule
 
 module LDPE (...);
@@ -2385,7 +2502,10 @@ module LDPE (...);
     parameter MSGON = "TRUE";
     parameter XON = "TRUE";
     output Q;
-    input D, G, GE, PRE;
+    input D;
+    input G;
+    input GE;
+    input PRE;
 endmodule
 
 module MMCME2_ADV (...);
@@ -2533,7 +2653,10 @@ module OBUFDS (...);
     parameter CAPACITANCE = "DONT_CARE";
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
-    output O, OB;
+    (* iopad_external_pin *)
+    output O;
+    (* iopad_external_pin *)
+    output OB;
     input I;
 endmodule
 
@@ -2542,20 +2665,27 @@ module OBUFT (...);
     parameter integer DRIVE = 12;
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
+    (* iopad_external_pin *)
     output O;
-    input I, T;
+    input I;
+    input T;
 endmodule
 
 module OBUFTDS (...);
     parameter CAPACITANCE = "DONT_CARE";
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
-    output O, OB;
-    input I, T;
+    (* iopad_external_pin *)
+    output O;
+    (* iopad_external_pin *)
+    output OB;
+    input I;
+    input T;
 endmodule
 
 module ODDR (...);
     output Q;
+    (* clkbuf_sink *)
     input C;
     input CE;
     input D1;
@@ -2586,6 +2716,7 @@ module ODELAYE2 (...);
     parameter integer SIM_DELAY_D = 0;
     output [4:0] CNTVALUEOUT;
     output DATAOUT;
+    (* clkbuf_sink *)
     input C;
     input CE;
     input CINVCTRL;
@@ -2631,7 +2762,9 @@ module OSERDESE2 (...);
     output TBYTEOUT;
     output TFB;
     output TQ;
+    (* clkbuf_sink *)
     input CLK;
+    (* clkbuf_sink *)
     input CLKDIV;
     input D1;
     input D2;
@@ -2673,9 +2806,11 @@ module OUT_FIFO (...);
     output [3:0] Q9;
     output [7:0] Q5;
     output [7:0] Q6;
+    (* clkbuf_sink *)
     input RDCLK;
     input RDEN;
     input RESET;
+    (* clkbuf_sink *)
     input WRCLK;
     input WREN;
     input [7:0] D0;
@@ -3659,7 +3794,17 @@ module RAM128X1S (...);
     parameter [127:0] INIT = 128'h00000000000000000000000000000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
     output O;
-    input A0, A1, A2, A3, A4, A5, A6, D, WCLK, WE;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input A6;
+    input D;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM256X1S (...);
@@ -3668,6 +3813,7 @@ module RAM256X1S (...);
     output O;
     input [7:0] A;
     input D;
+    (* clkbuf_sink *)
     input WCLK;
     input WE;
 endmodule
@@ -3690,6 +3836,7 @@ module RAM32M (...);
     input [1:0] DIB;
     input [1:0] DIC;
     input [1:0] DID;
+    (* clkbuf_sink *)
     input WCLK;
     input WE;
 endmodule
@@ -3698,22 +3845,48 @@ module RAM32X1S (...);
     parameter [31:0] INIT = 32'h00000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
     output O;
-    input A0, A1, A2, A3, A4, D, WCLK, WE;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input D;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM32X1S_1 (...);
     parameter [31:0] INIT = 32'h00000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
     output O;
-    input A0, A1, A2, A3, A4, D, WCLK, WE;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input D;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM32X2S (...);
     parameter [31:0] INIT_00 = 32'h00000000;
     parameter [31:0] INIT_01 = 32'h00000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
-    output O0, O1;
-    input A0, A1, A2, A3, A4, D0, D1, WCLK, WE;
+    output O0;
+    output O1;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input D0;
+    input D1;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM64M (...);
@@ -3734,6 +3907,7 @@ module RAM64M (...);
     input DIB;
     input DIC;
     input DID;
+    (* clkbuf_sink *)
     input WCLK;
     input WE;
 endmodule
@@ -3742,46 +3916,97 @@ module RAM64X1S (...);
     parameter [63:0] INIT = 64'h0000000000000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
     output O;
-    input A0, A1, A2, A3, A4, A5, D, WCLK, WE;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input D;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM64X1S_1 (...);
     parameter [63:0] INIT = 64'h0000000000000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
     output O;
-    input A0, A1, A2, A3, A4, A5, D, WCLK, WE;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input D;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module RAM64X2S (...);
     parameter [63:0] INIT_00 = 64'h0000000000000000;
     parameter [63:0] INIT_01 = 64'h0000000000000000;
     parameter [0:0] IS_WCLK_INVERTED = 1'b0;
-    output O0, O1;
-    input A0, A1, A2, A3, A4, A5, D0, D1, WCLK, WE;
+    output O0;
+    output O1;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input D0;
+    input D1;
+    (* clkbuf_sink *)
+    input WCLK;
+    input WE;
 endmodule
 
 module ROM128X1 (...);
     parameter [127:0] INIT = 128'h00000000000000000000000000000000;
     output O;
-    input A0, A1, A2, A3, A4, A5, A6;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input A6;
 endmodule
 
 module ROM256X1 (...);
     parameter [255:0] INIT = 256'h0000000000000000000000000000000000000000000000000000000000000000;
     output O;
-    input A0, A1, A2, A3, A4, A5, A6, A7;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
+    input A6;
+    input A7;
 endmodule
 
 module ROM32X1 (...);
     parameter [31:0] INIT = 32'h00000000;
     output O;
-    input A0, A1, A2, A3, A4;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
 endmodule
 
 module ROM64X1 (...);
     parameter [63:0] INIT = 64'h0000000000000000;
     output O;
-    input A0, A1, A2, A3, A4, A5;
+    input A0;
+    input A1;
+    input A2;
+    input A3;
+    input A4;
+    input A5;
 endmodule
 
 (* keep *)
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index 87f4af8f7..f058da83d 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -63,6 +63,9 @@ struct SynthXilinxPass : public ScriptPass
 		log("        generate an output netlist (and BLIF file) suitable for VPR\n");
 		log("        (this feature is experimental and incomplete)\n");
 		log("\n");
+		log("    -ise\n");
+		log("        generate an output netlist suitable for ISE (enables -iopad)\n");
+		log("\n");
 		log("    -nobram\n");
 		log("        do not use block RAM cells in output netlist\n");
 		log("\n");
@@ -78,6 +81,15 @@ struct SynthXilinxPass : public ScriptPass
 		log("    -nowidelut\n");
 		log("        do not use MUXF[78] resources to implement LUTs larger than LUT6s\n");
 		log("\n");
+		log("    -iopad\n");
+		log("        enable I/O buffer insertion (selected automatically by -ise)\n");
+		log("\n");
+		log("    -noiopad\n");
+		log("        disable I/O buffer insertion (only useful with -ise)\n");
+		log("\n");
+		log("    -noclkbuf\n");
+		log("        disable automatic clock buffer insertion\n");
+		log("\n");
 		log("    -widemux <int>\n");
 		log("        enable inference of hard multiplexer resources (MUXF[78]) for muxes at or\n");
 		log("        above this number of inputs (minimum value 2, recommended value >= 5).\n");
@@ -104,7 +116,7 @@ struct SynthXilinxPass : public ScriptPass
 	}
 
 	std::string top_opt, edif_file, blif_file, family;
-	bool flatten, retime, vpr, nobram, nolutram, nosrl, nocarry, nowidelut, abc9;
+	bool flatten, retime, vpr, ise, iopad, noiopad, noclkbuf, nobram, nolutram, nosrl, nocarry, nowidelut, abc9;
 	bool flatten_before_abc;
 	int widemux;
 
@@ -117,6 +129,10 @@ struct SynthXilinxPass : public ScriptPass
 		flatten = false;
 		retime = false;
 		vpr = false;
+		ise = false;
+		iopad = false;
+		noiopad = false;
+		noclkbuf = false;
 		nocarry = false;
 		nobram = false;
 		nolutram = false;
@@ -184,6 +200,22 @@ struct SynthXilinxPass : public ScriptPass
 				vpr = true;
 				continue;
 			}
+			if (args[argidx] == "-ise") {
+				ise = true;
+				continue;
+			}
+			if (args[argidx] == "-iopad") {
+				iopad = true;
+				continue;
+			}
+			if (args[argidx] == "-noiopad") {
+				noiopad = true;
+				continue;
+			}
+			if (args[argidx] == "-noclkbuf") {
+				noclkbuf = true;
+				continue;
+			}
 			if (args[argidx] == "-nocarry") {
 				nocarry = true;
 				continue;
@@ -421,6 +453,18 @@ struct SynthXilinxPass : public ScriptPass
 			run("clean");
 		}
 
+		if (check_label("finalize")) {
+			bool do_iopad = iopad || (ise && !noiopad);
+			if (help_mode || !noclkbuf) {
+				if (help_mode || do_iopad)
+					run("clkbufmap -buf BUFG O:I -inpad IBUFG O:I", "(skip if '-noclkbuf', '-inpad' passed if '-iopad' or '-ise' and not '-noiopad')");
+				else
+					run("clkbufmap -buf BUFG O:I");
+			}
+			if (do_iopad)
+				run("iopadmap -bits -outpad OBUF I:O -inpad IBUF O:I A:top", "(only if '-iopad' or '-ise' and not '-noiopad')");
+		}
+
 		if (check_label("check")) {
 			run("hierarchy -check");
 			run("stat -tech xilinx");
diff --git a/techlibs/xilinx/xc6s_brams_bb.v b/techlibs/xilinx/xc6s_brams_bb.v
index eb1a29579..041d6b54f 100644
--- a/techlibs/xilinx/xc6s_brams_bb.v
+++ b/techlibs/xilinx/xc6s_brams_bb.v
@@ -1,5 +1,7 @@
 module RAMB8BWER (
+	(* clkbuf_sink *)
 	input CLKAWRCLK,
+	(* clkbuf_sink *)
 	input CLKBRDCLK,
 	input ENAWREN,
 	input ENBRDEN,
@@ -87,7 +89,9 @@ module RAMB8BWER (
 endmodule
 
 module RAMB16BWER (
+	(* clkbuf_sink *)
 	input CLKA,
+	(* clkbuf_sink *)
 	input CLKB,
 	input ENA,
 	input ENB,
diff --git a/techlibs/xilinx/xc7_brams_bb.v b/techlibs/xilinx/xc7_brams_bb.v
index a682ba4a7..a43b4b5a1 100644
--- a/techlibs/xilinx/xc7_brams_bb.v
+++ b/techlibs/xilinx/xc7_brams_bb.v
@@ -1,5 +1,7 @@
 module RAMB18E1 (
+	(* clkbuf_sink *)
 	input CLKARDCLK,
+	(* clkbuf_sink *)
 	input CLKBWRCLK,
 	input ENARDEN,
 	input ENBWREN,
@@ -123,7 +125,9 @@ module RAMB18E1 (
 endmodule
 
 module RAMB36E1 (
+	(* clkbuf_sink *)
 	input CLKARDCLK,
+	(* clkbuf_sink *)
 	input CLKBWRCLK,
 	input ENARDEN,
 	input ENBWREN,
diff --git a/tests/techmap/.gitignore b/tests/techmap/.gitignore
index 397b4a762..cfed22fc5 100644
--- a/tests/techmap/.gitignore
+++ b/tests/techmap/.gitignore
@@ -1 +1,2 @@
 *.log
+/*.mk
diff --git a/tests/techmap/clkbufmap.ys b/tests/techmap/clkbufmap.ys
new file mode 100644
index 000000000..f1277864e
--- /dev/null
+++ b/tests/techmap/clkbufmap.ys
@@ -0,0 +1,96 @@
+read_verilog <<EOT
+module clkbuf (input i, (* clkbuf_driver *) output o); endmodule
+module dff ((* clkbuf_sink *) input clk, input d, output q); endmodule
+module dffe ((* clkbuf_sink *) input c, input d, e, output q); endmodule
+module latch (input e, d, output q); endmodule
+module clkgen (output o); endmodule
+
+module top(input clk1, clk2, clk3, d, e, output [4:0] q);
+wire clk4, clk5, clk6;
+dff s0 (.clk(clk1), .d(d), .q(q[0]));
+dffe s1 (.c(clk2), .d(d), .e(e), .q(q[1]));
+latch s2 (.e(clk3), .d(d), .q(q[2]));
+sub s3 (.sclk4(clk4), .sclk5(clk5), .sclk6(clk6), .sd(d), .sq(q[3]));
+dff s4 (.clk(clk4), .d(d), .q(q[4]));
+dff s5 (.clk(clk5), .d(d), .q(q[4]));
+dff s6 (.clk(clk6), .d(d), .q(q[4]));
+endmodule
+
+module sub(output sclk4, output sclk5, output sclk6, input sd, output sq);
+wire tmp;
+clkgen s7(.o(sclk4));
+clkgen s8(.o(sclk5));
+clkgen s9(.o(tmp));
+clkbuf s10(.i(tmp), .o(sclk6));
+dff s11(.clk(sclk4), .d(sd), .q(sq));
+endmodule
+EOT
+
+hierarchy -auto-top
+design -save ref
+
+# ----------------------
+
+design -load ref
+clkbufmap -buf clkbuf o:i
+select -assert-count 3 top/t:clkbuf
+select -assert-count 2 sub/t:clkbuf
+select -set clk1 w:clk1 %a %co t:clkbuf %i          # Find 'clk1' fanouts that are 'clkbuf'
+select -assert-count 1 @clk1                        # Check there is one such fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s* %i    # Check that the 'o' of that clkbuf drives one fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s0 %i    # And that one fanout is 's0'
+select -set clk2 w:clk2 %a %co t:clkbuf %i
+select -assert-count 1 @clk2
+select -assert-count 1 @clk2 %x:+[o] %co c:s* %i
+select -assert-count 1 @clk2 %x:+[o] %co c:s1 %i
+select -set clk5 w:clk5 %a %ci t:clkbuf %i
+select -assert-count 1 @clk5
+select -assert-count 1 @clk5 %x:+[o] %co c:s5 %i
+select -assert-count 1 @clk5 %x:+[i] %ci c:s3 %i
+select -set sclk4 w:sclk4 %a %ci t:clkbuf %i
+select -assert-count 1 @sclk4
+select -assert-count 1 @sclk4 %x:+[o] %co c:s11 %i
+select -assert-count 1 @sclk4 %x:+[i] %ci c:s7 %i
+
+# ----------------------
+
+design -load ref
+setattr -set clkbuf_inhibit 0 w:clk1
+setattr -set clkbuf_inhibit 1 w:clk2
+clkbufmap -buf clkbuf o:i
+select -assert-count 2 top/t:clkbuf
+select -set clk1 w:clk1 %a %co t:clkbuf %i          # Find 'clk1' fanouts that are 'clkbuf'
+select -assert-count 1 @clk1                        # Check there is one such fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s* %i    # Check that the 'o' of that clkbuf drives one fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s0 %i    # And that one fanout is 's0'
+select -assert-count 0 w:clk2 %a %co t:clkbuf %i
+
+# ----------------------
+
+design -load ref
+setattr -set clkbuf_inhibit 1 w:clk1
+setattr -set buffer_type "bufg" w:clk2
+clkbufmap -buf clkbuf o:i w:* a:buffer_type=none a:buffer_type=bufr %u %d
+select -assert-count 3 top/t:clkbuf
+select -assert-count 2 sub/t:clkbuf
+select -set clk1 w:clk1 %a %co t:clkbuf %i          # Find 'clk1' fanouts that are 'clkbuf'
+select -assert-count 1 @clk1                        # Check there is one such fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s* %i    # Check that the 'o' of that clkbuf drives one fanout
+select -assert-count 1 @clk1 %x:+[o] %co c:s0 %i    # And that one fanout is 's0'
+select -set clk2 w:clk2 %a %co t:clkbuf %i          # Find 'clk1' fanouts that are 'clkbuf'
+select -assert-count 1 @clk2                        # Check there is one such fanout
+select -assert-count 1 @clk2 %x:+[o] %co c:s* %i    # Check that the 'o' of that clkbuf drives one fanout
+select -assert-count 1 @clk2 %x:+[o] %co c:s1 %i    # And that one fanout is 's0'
+
+# ----------------------
+
+design -load ref
+setattr -set buffer_type "none" w:clk1
+setattr -set buffer_type "bufr" w:clk2
+setattr -set buffer_type "bufr" w:sclk4
+setattr -set buffer_type "bufr" w:sclk5
+clkbufmap -buf clkbuf o:i w:* a:buffer_type=none a:buffer_type=bufr %u %d
+select -assert-count 0 w:clk1 %a %co t:clkbuf %i
+select -assert-count 0 w:clk2 %a %co t:clkbuf %i
+select -assert-count 0 top/t:clkbuf
+select -assert-count 1 sub/t:clkbuf
diff --git a/tests/techmap/run-test.sh b/tests/techmap/run-test.sh
index e2fc11e52..96489ff15 100755
--- a/tests/techmap/run-test.sh
+++ b/tests/techmap/run-test.sh
@@ -1,10 +1,20 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -e
-for x in *_runtest.sh; do
-	echo "Running $x.."
-	if ! bash $x &> ${x%.sh}.log; then
-		tail ${x%.sh}.log
-		echo ERROR
-		exit 1
+{
+echo "all::"
+for x in *.ys; do
+	echo "all:: run-$x"
+	echo "run-$x:"
+	echo "	@echo 'Running $x..'"
+	echo "	@../../yosys -ql ${x%.ys}.log $x"
+done
+for s in *.sh; do
+	if [ "$s" != "run-test.sh" ]; then
+		echo "all:: run-$s"
+		echo "run-$s:"
+		echo "	@echo 'Running $s..'"
+		echo "	@bash $s > ${s%.sh}.log 2>&1"
 	fi
 done
+} > run-test.mk
+exec ${MAKE:-make} -f run-test.mk