diff --git a/backends/btor/Makefile.inc b/backends/btor/Makefile.inc
new file mode 100644
index 000000000..af7ab14dc
--- /dev/null
+++ b/backends/btor/Makefile.inc
@@ -0,0 +1,3 @@
+
+OBJS += backends/btor/btor.o
+
diff --git a/backends/btor/btor.cc b/backends/btor/btor.cc
new file mode 100644
index 000000000..f5babebce
--- /dev/null
+++ b/backends/btor/btor.cc
@@ -0,0 +1,973 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *  Copyright (C) 2014  Ahmed Irfan <irfan@fbk.eu>
+ *  
+ *  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.
+ *
+ */
+
+// [[CITE]] BTOR: Bit-Precise Modelling of Word-Level Problems for Model Checking 
+// Johannes Kepler University, Linz, Austria
+// http://fmv.jku.at/papers/BrummayerBiereLonsing-BPR08.pdf
+
+#include "kernel/rtlil.h"
+#include "kernel/register.h"
+#include "kernel/sigtools.h"
+#include "kernel/celltypes.h"
+#include "kernel/log.h"
+#include <string>
+#include <assert.h>
+#include <math.h>
+
+struct BtorDumperConfig
+{
+	bool subckt_mode;
+	bool conn_mode;
+	bool impltf_mode;
+
+	std::string buf_type, buf_in, buf_out;
+	std::string true_type, true_out, false_type, false_out;
+
+	BtorDumperConfig() : subckt_mode(false), conn_mode(false), impltf_mode(false) { }
+};
+
+struct WireInfo
+{
+	RTLIL::IdString cell_name;
+	RTLIL::SigChunk *chunk;
+
+	WireInfo(RTLIL::IdString c, RTLIL::SigChunk* ch) : cell_name(c), chunk(ch) { }
+};
+
+struct WireInfoOrder
+{
+	bool operator() (const WireInfo& x, const WireInfo& y)
+	{
+		return x.chunk < y.chunk;
+	}
+};
+
+struct BtorDumper
+{
+	FILE *f;
+	RTLIL::Module *module;
+	RTLIL::Design *design;
+	BtorDumperConfig *config;
+	CellTypes ct;
+
+	SigMap sigmap;
+	std::map<RTLIL::IdString, std::set<WireInfo,WireInfoOrder>> inter_wire_map;//<wire, dependency list> for maping the intermediate wires that are output of some cell
+	std::map<RTLIL::IdString, int> line_ref;//mapping of ids to line_num of the btor file
+	std::map<RTLIL::SigSpec, int> sig_ref;//mapping of sigspec to the line_num of the btor file
+	int line_num;//last line number of btor file
+	std::string str;//temp string for writing file
+	std::map<RTLIL::IdString, bool> basic_wires;//input wires and registers	
+	RTLIL::IdString curr_cell; //current cell being dumped
+	std::map<std::string, std::string> cell_type_translation, s_cell_type_translation; //RTLIL to BTOR translation
+	BtorDumper(FILE *f, RTLIL::Module *module, RTLIL::Design *design, BtorDumperConfig *config) :
+			f(f), module(module), design(design), config(config), ct(design), sigmap(module)
+	{
+		line_num=0;
+		str.clear();
+		for(auto it=module->wires.begin(); it!=module->wires.end(); ++it)
+		{
+			if(it->second->port_input)
+			{
+				basic_wires[it->first]=true;
+			}
+			else
+			{
+				basic_wires[it->first]=false;
+			}
+			inter_wire_map[it->first].clear();
+		}
+		curr_cell.clear();
+		//assert
+		cell_type_translation["$assert"] = "root";
+		//unary
+		cell_type_translation["$not"] = "not";
+		cell_type_translation["$neg"] = "neg";
+		cell_type_translation["$reduce_and"] = "redand";
+		cell_type_translation["$reduce_or"] = "redor";
+		cell_type_translation["$reduce_xor"] = "redxor";
+		cell_type_translation["$reduce_bool"] = "redor";
+		//binary
+		cell_type_translation["$and"] = "and";
+		cell_type_translation["$or"] = "or";
+		cell_type_translation["$xor"] = "xor";
+		cell_type_translation["$xnor"] = "xnor";
+		cell_type_translation["$shr"] = "srl";
+		cell_type_translation["$shl"] = "sll";
+		cell_type_translation["$sshr"] = "sra";
+		cell_type_translation["$sshl"] = "sll";
+		cell_type_translation["$lt"] = "ult";
+		cell_type_translation["$le"] = "ulte";
+		cell_type_translation["$gt"] = "ugt";
+		cell_type_translation["$ge"] = "ugte";
+		cell_type_translation["$eq"] = "eq";
+		cell_type_translation["$eqx"] = "eq";
+		cell_type_translation["$ne"] = "ne";
+		cell_type_translation["$nex"] = "ne";
+		cell_type_translation["$add"] = "add";
+		cell_type_translation["$sub"] = "sub";
+		cell_type_translation["$mul"] = "mul";
+		cell_type_translation["$mod"] = "urem";
+		cell_type_translation["$div"] = "udiv";
+		//mux
+		cell_type_translation["$mux"] = "cond";
+		//reg
+		cell_type_translation["$dff"] = "next";
+		cell_type_translation["$adff"] = "next";
+		cell_type_translation["$dffsr"] = "next";
+		//memories
+		//nothing here
+
+		//signed cell type translation 
+		//binary
+		s_cell_type_translation["$modx"] = "srem";
+		s_cell_type_translation["$mody"] = "smod";
+		s_cell_type_translation["$div"] = "sdiv";
+		s_cell_type_translation["$lt"] = "slt";
+		s_cell_type_translation["$le"] = "slte";
+		s_cell_type_translation["$gt"] = "sgt";
+		s_cell_type_translation["$ge"] = "sgte";
+		 
+	}
+	
+	std::vector<std::string> cstr_buf;
+
+	const char *cstr(const RTLIL::IdString id)
+	{
+		str = RTLIL::unescape_id(id);
+		for (size_t i = 0; i < str.size(); ++i)
+			if (str[i] == '#' || str[i] == '=')
+				str[i] = '?';
+		cstr_buf.push_back(str);
+		return cstr_buf.back().c_str();
+	}
+	
+	int dump_wire(RTLIL::Wire* wire)
+	{
+		if(basic_wires[wire->name])
+		{	
+			log("writing wire %s\n", cstr(wire->name));
+			auto it = line_ref.find(wire->name);
+			if(it==std::end(line_ref))
+			{
+				++line_num;
+				line_ref[wire->name]=line_num;			
+				str = stringf("%d var %d %s", line_num, wire->width, cstr(wire->name));
+				fprintf(f, "%s\n", str.c_str());
+				return line_num;
+			}
+			else return it->second;
+		}
+		else // case when the wire is not basic wire
+		{
+			log("case of non-basic wire - %s\n", cstr(wire->name));
+			auto it = line_ref.find(wire->name);
+			if(it==std::end(line_ref))
+			{
+				std::set<WireInfo, WireInfoOrder>& dep_set = inter_wire_map.at(wire->name);
+				int wire_line = 0;
+				int wire_width = 0;
+				for(auto dep_set_it=dep_set.begin(); dep_set_it!=dep_set.end(); ++dep_set_it)
+				{
+					RTLIL::IdString cell_id = dep_set_it->cell_name;
+					if(cell_id == curr_cell)
+						break;
+					log(" -- found cell %s\n", cstr(cell_id));
+					RTLIL::Cell* cell = module->cells.at(cell_id);
+					RTLIL::SigSpec* cell_output = get_cell_output(cell);
+					int cell_line = dump_cell(cell);				
+
+					if(dep_set.size()==1 && wire->width == cell_output->width)
+					{
+						wire_line = cell_line;
+						break;
+					}
+					else
+					{
+						int prev_wire_line=0; //previously dumped wire line
+						int start_bit=0;
+						for(unsigned j=0; j<cell_output->chunks.size(); ++j)
+						{
+							start_bit+=cell_output->chunks[j].width;
+							if(cell_output->chunks[j].wire->name == wire->name)
+							{
+								prev_wire_line = wire_line;
+								wire_line = ++line_num;
+								str = stringf("%d slice %d %d %d %d;1", line_num, cell_output->chunks[j].width,
+ 									cell_line, start_bit-1, start_bit-cell_output->chunks[j].width);
+								fprintf(f, "%s\n", str.c_str());
+								wire_width += cell_output->chunks[j].width;
+								if(prev_wire_line!=0)
+								{
+									++line_num;
+									str = stringf("%d concat %d %d %d", line_num, wire_width, wire_line, prev_wire_line);
+									fprintf(f, "%s\n", str.c_str());
+									wire_line = line_num;
+								}
+							}
+						}
+					}
+				}
+				if(dep_set.size()==0)
+				{
+					log(" - checking sigmap\n");						
+					RTLIL::SigSpec s = RTLIL::SigSpec(wire);
+					wire_line = dump_sigspec(&s, s.width);
+					line_ref[wire->name]=wire_line;
+				}
+				line_ref[wire->name]=wire_line;
+				return wire_line;
+			}
+			else 
+			{
+				log(" -- already processed wire\n");			
+				return it->second;
+			}
+		}
+		assert(false);
+		return -1;
+	}
+	
+	int dump_memory(const RTLIL::Memory* memory)
+	{
+		log("writing memory %s\n", cstr(memory->name));
+		auto it = line_ref.find(memory->name);
+		if(it==std::end(line_ref))
+		{
+			++line_num;
+			int address_bits = ceil(log(memory->size)/log(2));
+			str = stringf("%d array %d %d", line_num, memory->width, address_bits);
+			line_ref[memory->name]=line_num;			
+			fprintf(f, "%s\n", str.c_str());
+			return line_num;
+		}
+		else return it->second;
+	}
+
+	int dump_const(const RTLIL::Const* data, int width, int offset)
+	{
+		log("writing const \n");
+		if((data->flags & RTLIL::CONST_FLAG_STRING) == 0)
+		{
+			if(width<0)
+				width = data->bits.size() - offset;
+
+			std::string data_str = data->as_string();
+			//if(offset > 0)
+				data_str = data_str.substr(offset, width);
+
+			++line_num;
+			str = stringf("%d const %d %s", line_num, width, data_str.c_str());
+			fprintf(f, "%s\n", str.c_str());
+			return line_num;
+		}
+		else
+			log("writing const error\n");		
+		assert(false);
+		return -1;
+	}
+	
+	int dump_sigchunk(const RTLIL::SigChunk* chunk)
+	{
+		log("writing sigchunk\n");
+		int l=-1;
+		if(chunk->wire == NULL)
+		{
+			l=dump_const(&chunk->data, chunk->width, chunk->offset);			
+		}
+		else
+		{
+			if (chunk->width == chunk->wire->width && chunk->offset == 0)
+				l = dump_wire(chunk->wire);
+			else 
+			{
+				int wire_line_num = dump_wire(chunk->wire);
+				assert(wire_line_num>0);
+				++line_num;
+				str = stringf("%d slice %d %d %d %d;2", line_num, chunk->width, wire_line_num, 
+					chunk->width + chunk->offset - 1, chunk->offset);
+				fprintf(f, "%s\n", str.c_str());
+				l = line_num;				 
+			}
+		}
+		return l;
+	}
+
+	int dump_sigspec(const RTLIL::SigSpec* sig, int expected_width)
+	{
+		log("writing sigspec\n");
+		RTLIL::SigSpec s = sigmap(*sig);
+		int l = -1;
+		auto it = sig_ref.find(s);
+		if(it == std::end(sig_ref))
+		{
+			if (s.chunks.size() == 1) 
+			{
+				l = dump_sigchunk(&s.chunks[0]);
+			} 
+			else 
+			{
+				int l1, l2, w1, w2;
+				l1 = dump_sigchunk(&s.chunks[0]);
+				assert(l1>0);
+				w1 = s.chunks[0].width;
+				for (unsigned i=1; i < s.chunks.size(); ++i)
+				{
+					l2 = dump_sigchunk(&s.chunks[i]);
+					assert(l2>0);
+					w2 = s.chunks[i].width;
+					++line_num;
+					str = stringf("%d concat %d %d %d", line_num, w1+w2, l2, l1);
+					fprintf(f, "%s\n", str.c_str());
+					l1=line_num;
+					w1+=w2;
+				}
+				l = line_num;
+			}
+			sig_ref[s] = l;
+		}
+		else
+		{
+			l = it->second;
+		}
+		
+		if (expected_width != s.width)
+		{
+			log(" - changing width of sigspec\n");
+			//TODO: save the new signal in map
+			/*if(expected_width > s.width)
+				s.extend_u0(expected_width);
+			else if (expected_width < s.width)
+				s = s.extract(0, expected_width);
+			
+			it = sig_ref.find(s);
+			if(it == std::end(sig_ref))
+			{*/
+				if(expected_width > s.width)
+				{
+					//TODO: case the signal is signed
+					++line_num;
+					str = stringf ("%d zero %d", line_num, expected_width - s.width);
+					fprintf(f, "%s\n", str.c_str());
+					++line_num;
+					str = stringf ("%d concat %d %d %d", line_num, expected_width, line_num-1, l);
+					fprintf(f, "%s\n", str.c_str());
+					l = line_num;
+				}
+				else if(expected_width < s.width)
+				{
+					++line_num;
+					str = stringf ("%d slice %d %d %d %d;3", line_num, expected_width, l, expected_width-1, 0);
+					fprintf(f, "%s\n", str.c_str());
+					l = line_num;
+				}
+				/*sig_ref[s] = l;
+			}
+			else
+			{
+				l = it->second;
+			}*/
+		}
+		assert(l>0);
+		return l;
+	}
+	
+	int dump_cell(const RTLIL::Cell* cell)
+	{
+		auto it = line_ref.find(cell->name);
+		if(it==std::end(line_ref))
+		{
+			curr_cell = cell->name;
+			//assert cell
+			if(cell->type == "$assert")
+			{
+				log("writing assert cell - %s\n", cstr(cell->type));
+				const RTLIL::SigSpec* expr = &cell->connections.at(RTLIL::IdString("\\A"));
+				const RTLIL::SigSpec* en = &cell->connections.at(RTLIL::IdString("\\EN"));
+				assert(expr->width == 1);
+				assert(en->width == 1);
+				int expr_line = dump_sigspec(expr, 1);
+				int en_line = dump_sigspec(en, 1);
+				int one_line = ++line_num;
+				str = stringf("%d one 1", line_num);
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d %s %d %d %d", line_num, cell_type_translation.at("$eq").c_str(), 1, en_line, one_line);
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d %s %d %d %d %d", line_num, cell_type_translation.at("$mux").c_str(), 1, line_num-1,
+					expr_line, one_line);
+				fprintf(f, "%s\n", str.c_str());
+				int cell_line = ++line_num;
+				str = stringf("%d %s %d %d", line_num, cell_type_translation.at("$assert").c_str(), 1, line_num-1);
+				fprintf(f, "%s\n", str.c_str());
+				line_ref[cell->name]=cell_line;
+			}
+			//unary cells
+			if(cell->type == "$not" || cell->type == "$neg" || cell->type == "$pos" || cell->type == "$reduce_and" ||
+				cell->type == "$reduce_or" || cell->type == "$reduce_xor" || cell->type == "$reduce_bool")
+			{
+				log("writing unary cell - %s\n", cstr(cell->type));
+				int w = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				w = w>output_width ? w:output_width; //padding of w
+				int l = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), w);				
+				int cell_line = l;
+				if(cell->type != "$pos")
+				{	
+					cell_line = ++line_num;
+					bool reduced = (cell->type == "$not" || cell->type == "$neg") ? false : true;
+					str = stringf ("%d %s %d %d", cell_line, cell_type_translation.at(cell->type).c_str(), reduced?output_width:w, l);
+					fprintf(f, "%s\n", str.c_str());
+				}
+				if(output_width < w && (cell->type == "$not" || cell->type == "$neg" || cell->type == "$pos"))
+				{
+					++line_num;
+					str = stringf ("%d slice %d %d %d %d;4", line_num, output_width, cell_line, output_width-1, 0);
+					fprintf(f, "%s\n", str.c_str());
+					cell_line = line_num;
+				}				
+				line_ref[cell->name]=cell_line;
+			}
+			else if(cell->type == "$reduce_xnor" || cell->type == "$logic_not")//no direct translation in btor
+			{
+				log("writing unary cell - %s\n", cstr(cell->type));
+				int w = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				assert(output_width == 1);
+				int l = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), w);
+				if(cell->type == "$logic_not" && w > 1)
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d", line_num, cell_type_translation.at("$reduce_or").c_str(), output_width, l);
+					fprintf(f, "%s\n", str.c_str());
+				}
+				else if(cell->type == "$reduce_xnor")
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d", line_num, cell_type_translation.at("$reduce_xor").c_str(), output_width, l);
+					fprintf(f, "%s\n", str.c_str());
+				}		
+				++line_num;
+				str = stringf ("%d %s %d %d", line_num, cell_type_translation.at("$not").c_str(), output_width, line_num-1);
+				fprintf(f, "%s\n", str.c_str());
+				line_ref[cell->name]=line_num;
+			}
+			//binary cells
+			else if(cell->type == "$and" || cell->type == "$or" || cell->type == "$xor" || cell->type == "$xnor" ||
+				 cell->type == "$lt" || cell->type == "$le" || cell->type == "$eq" || cell->type == "$ne" || 
+				 cell->type == "$eqx" || cell->type == "$nex" || cell->type == "$ge" || cell->type == "$gt" )
+			{
+				log("writing binary cell - %s\n", cstr(cell->type));
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				assert(!(cell->type == "$eq" || cell->type == "$ne" || cell->type == "$eqx" || cell->type == "$nex" ||
+					cell->type == "$ge" || cell->type == "$gt") || output_width == 1);
+				bool l1_signed = cell->parameters.at(RTLIL::IdString("\\A_SIGNED")).as_bool();
+				bool l2_signed = cell->parameters.at(RTLIL::IdString("\\B_SIGNED")).as_bool();
+				int l1_width = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				int l2_width = 	cell->parameters.at(RTLIL::IdString("\\B_WIDTH")).as_int();
+				
+				assert(l1_signed == l2_signed);
+				l1_width = l1_width > output_width ? l1_width : output_width;					
+				l1_width = l1_width > l2_width ? l1_width : l2_width;
+				l2_width = l2_width > l1_width ? l2_width : l1_width;
+
+				int l1 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), l1_width);
+				int l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), l2_width);
+				
+				++line_num;
+				std::string op = cell_type_translation.at(cell->type);
+				if(cell->type == "$lt" || cell->type == "$le" ||
+				 cell->type == "$eq" || cell->type == "$ne" || cell->type == "$eqx" || cell->type == "$nex" ||
+				 cell->type == "$ge" || cell->type == "$gt")
+				{
+					if(l1_signed)
+						op = s_cell_type_translation.at(cell->type);
+				}
+				
+				str = stringf ("%d %s %d %d %d", line_num, op.c_str(), output_width, l1, l2);
+				fprintf(f, "%s\n", str.c_str());
+
+				line_ref[cell->name]=line_num;
+			}
+			else if(cell->type == "$add" || cell->type == "$sub" || cell->type == "$mul" || cell->type == "$div" || 
+				 cell->type == "$mod" )
+			{
+				//TODO: division by zero case
+				log("writing binary cell - %s\n", cstr(cell->type));
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				bool l1_signed = cell->parameters.at(RTLIL::IdString("\\A_SIGNED")).as_bool();
+				bool l2_signed = cell->parameters.at(RTLIL::IdString("\\B_SIGNED")).as_bool();
+				int l1_width = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				int l2_width = 	cell->parameters.at(RTLIL::IdString("\\B_WIDTH")).as_int();
+				
+				assert(l1_signed == l2_signed);
+				l1_width = l1_width > output_width ? l1_width : output_width;					
+				l1_width = l1_width > l2_width ? l1_width : l2_width;
+				l2_width = l2_width > l1_width ? l2_width : l1_width;
+
+				int l1 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), l1_width);
+				int l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), l2_width);
+				
+				++line_num;
+				std::string op = cell_type_translation.at(cell->type);
+				if(cell->type == "$div" && l1_signed)
+					op = s_cell_type_translation.at(cell->type);
+				else if(cell->type == "$mod")
+				{
+					if(l1_signed)
+						op = s_cell_type_translation.at("$modx");
+					else if(l2_signed)
+						op = s_cell_type_translation.at("$mody");
+				}
+				str = stringf ("%d %s %d %d %d", line_num, op.c_str(), l1_width, l1, l2);
+				fprintf(f, "%s\n", str.c_str());
+
+				if(output_width < l1_width)
+				{
+					++line_num;
+					str = stringf ("%d slice %d %d %d %d;5", line_num, output_width, line_num-1, output_width-1, 0);
+					fprintf(f, "%s\n", str.c_str());
+				}
+				line_ref[cell->name]=line_num;
+			}
+			else if(cell->type == "$shr" || cell->type == "$shl" || cell->type == "$sshr" || cell->type == "$sshl")
+			{
+				log("writing binary cell - %s\n", cstr(cell->type));
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				bool l1_signed = cell->parameters.at(RTLIL::IdString("\\A_SIGNED")).as_bool();
+				//bool l2_signed = cell->parameters.at(RTLIL::IdString("\\B_SIGNED")).as_bool();
+				int l1_width = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				l1_width = pow(2, ceil(log(l1_width)/log(2)));
+				int l2_width = 	cell->parameters.at(RTLIL::IdString("\\B_WIDTH")).as_int();
+				//assert(l2_width <= ceil(log(l1_width)/log(2)) );
+				int l1 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), l1_width);
+				int l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), ceil(log(l1_width)/log(2)));
+				int cell_output = ++line_num;
+				str = stringf ("%d %s %d %d %d", line_num, cell_type_translation.at(cell->type).c_str(), l1_width, l1, l2);
+				fprintf(f, "%s\n", str.c_str());
+
+				if(l2_width > ceil(log(l1_width)/log(2)))
+				{
+					int extra_width = l2_width - ceil(log(l1_width)/log(2));
+					l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), l2_width);
+					++line_num;
+					str = stringf ("%d slice %d %d %d %d;6", line_num, extra_width, l2, l2_width-1, l2_width-extra_width);
+					fprintf(f, "%s\n", str.c_str());
+					++line_num;
+					str = stringf ("%d one %d", line_num, extra_width);
+					fprintf(f, "%s\n", str.c_str());
+					int mux = ++line_num;
+					str = stringf ("%d %s %d %d %d", line_num, cell_type_translation.at("$gt").c_str(), 1, line_num-2, line_num-1);
+					fprintf(f, "%s\n", str.c_str());
+					++line_num;
+					str = stringf("%d %s %d", line_num, l1_signed && cell->type == "$sshr" ? "ones":"zero", l1_width);
+					fprintf(f, "%s\n", str.c_str());
+					++line_num;
+					str = stringf ("%d %s %d %d %d %d", line_num, cell_type_translation.at("$mux").c_str(), l1_width, mux, line_num-1, cell_output);
+					fprintf(f, "%s\n", str.c_str());
+					cell_output = line_num;
+				}
+
+				if(output_width < l1_width)
+				{
+					++line_num;
+					str = stringf ("%d slice %d %d %d %d;5", line_num, output_width, cell_output, output_width-1, 0);
+					fprintf(f, "%s\n", str.c_str());
+					cell_output = line_num;
+				}
+				line_ref[cell->name] = cell_output;	
+			}
+			else if(cell->type == "$logic_and" || cell->type == "$logic_or")//no direct translation in btor
+			{
+				log("writing binary cell - %s\n", cstr(cell->type));
+				int output_width = cell->parameters.at(RTLIL::IdString("\\Y_WIDTH")).as_int();
+				assert(output_width == 1);
+				int l1 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), output_width);
+				int l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), output_width);
+				int l1_width = cell->parameters.at(RTLIL::IdString("\\A_WIDTH")).as_int();
+				int l2_width = 	cell->parameters.at(RTLIL::IdString("\\B_WIDTH")).as_int();
+				if(l1_width >1)
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d", line_num, cell_type_translation.at("$reduce_or").c_str(), output_width, l1);
+					fprintf(f, "%s\n", str.c_str());
+					l1 = line_num;
+				}
+				if(l2_width > 1)
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d", line_num, cell_type_translation.at("$reduce_or").c_str(), output_width, l2);
+					fprintf(f, "%s\n", str.c_str());
+					l2 = line_num;
+				}
+				if(cell->type == "$logic_and")
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d %d", line_num, cell_type_translation.at("$and").c_str(), output_width, l1, l2);
+				}
+				else if(cell->type == "$logic_or")
+				{
+					++line_num;
+					str = stringf ("%d %s %d %d %d", line_num, cell_type_translation.at("$or").c_str(), output_width, l1, l2);
+				}
+				fprintf(f, "%s\n", str.c_str());
+				line_ref[cell->name]=line_num;
+			}
+			//multiplexers
+			else if(cell->type == "$mux")
+			{
+				log("writing mux cell\n");
+				int output_width = cell->parameters.at(RTLIL::IdString("\\WIDTH")).as_int();
+				int l1 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\A")), output_width);
+				int l2 = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\B")), output_width);
+				int s = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\S")), 1);
+				++line_num;
+				str = stringf ("%d %s %d %d %d %d", 
+					line_num, cell_type_translation.at(cell->type).c_str(), output_width, s, l2, l1);//if s is 0 then l1, if s is 1 then l2 //according to the implementation of mux cell
+				fprintf(f, "%s\n", str.c_str());
+				line_ref[cell->name]=line_num;
+			}
+			//registers
+			else if(cell->type == "$dff" || cell->type == "$adff" || cell->type == "$dffsr")
+			{
+				//TODO: remodelling fo adff cells
+				log("writing cell - %s\n", cstr(cell->type));
+				int output_width = cell->parameters.at(RTLIL::IdString("\\WIDTH")).as_int();
+				log(" - width is %d\n", output_width);
+				int cond = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\CLK")), 1);
+				bool polarity = cell->parameters.at(RTLIL::IdString("\\CLK_POLARITY")).as_bool();
+				const RTLIL::SigSpec* cell_output = &cell->connections.at(RTLIL::IdString("\\Q"));
+				int value = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\D")), output_width);
+				unsigned start_bit = 0;
+				for(unsigned i=0; i<cell_output->chunks.size(); ++i)
+				{
+					output_width = cell_output->chunks[i].width;
+					assert( output_width == cell_output->chunks[i].wire->width);//full reg is given the next value
+					int reg = dump_wire(cell_output->chunks[i].wire);//register
+					int slice = value;
+					if(cell_output->chunks.size()>1)
+					{
+						start_bit+=output_width;
+						slice = ++line_num;
+						str = stringf ("%d slice %d %d %d %d;", line_num, output_width, value, start_bit-1, 
+							start_bit-output_width);
+						fprintf(f, "%s\n", str.c_str());
+					}
+					if(cell->type == "$dffsr")
+					{
+						int sync_reset = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\CLR")), 1);
+						bool sync_reset_pol = cell->parameters.at(RTLIL::IdString("\\CLR_POLARITY")).as_bool();
+						int sync_reset_value = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\SET")),
+							output_width);
+						bool sync_reset_value_pol = cell->parameters.at(RTLIL::IdString("\\SET_POLARITY")).as_bool();
+						++line_num;
+						str = stringf ("%d %s %d %s%d %s%d %d", line_num, cell_type_translation.at("$mux").c_str(), 
+							output_width, sync_reset_pol ? "":"-", sync_reset, sync_reset_value_pol? "":"-", 
+							sync_reset_value, slice);
+						fprintf(f, "%s\n", str.c_str());
+						slice = line_num;
+					}
+					++line_num;
+					str = stringf ("%d %s %d %s%d %d %d", line_num, cell_type_translation.at("$mux").c_str(), 
+						output_width, polarity?"":"-", cond, slice, reg);
+				
+					fprintf(f, "%s\n", str.c_str());
+					int next = line_num;
+					if(cell->type == "$adff")
+					{
+						int async_reset = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\ARST")), 1);
+						bool async_reset_pol = cell->parameters.at(RTLIL::IdString("\\ARST_POLARITY")).as_bool();
+						int async_reset_value = dump_const(&cell->parameters.at(RTLIL::IdString("\\ARST_VALUE")),
+							output_width, 0);
+						++line_num;
+						str = stringf ("%d %s %d %s%d %d %d", line_num, cell_type_translation.at("$mux").c_str(), 
+							output_width, async_reset_pol ? "":"-", async_reset, async_reset_value, next);
+						fprintf(f, "%s\n", str.c_str());
+					}
+					++line_num;
+					str = stringf ("%d %s %d %d %d", line_num, cell_type_translation.at(cell->type).c_str(), 
+						output_width, reg, next);
+					fprintf(f, "%s\n", str.c_str());
+				}
+				line_ref[cell->name]=line_num;
+			}
+			//memories
+			else if(cell->type == "$memrd")
+			{
+				log("writing memrd cell\n");
+				str = cell->parameters.at(RTLIL::IdString("\\MEMID")).decode_string();
+				int mem = dump_memory(module->memories.at(RTLIL::IdString(str.c_str())));
+				int address_width = cell->parameters.at(RTLIL::IdString("\\ABITS")).as_int();
+				int address = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\ADDR")), address_width);
+				int data_width = cell->parameters.at(RTLIL::IdString("\\WIDTH")).as_int();
+				++line_num;
+				str = stringf("%d read %d %d %d", line_num, data_width, mem, address);	
+				fprintf(f, "%s\n", str.c_str());
+				line_ref[cell->name]=line_num;
+			}
+			else if(cell->type == "$memwr")
+			{
+				log("writing memwr cell\n");
+				int clk = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\CLK")), 1);
+				bool polarity = cell->parameters.at(RTLIL::IdString("\\CLK_POLARITY")).as_bool();
+				int enable = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\EN")), 1);
+				int address_width = cell->parameters.at(RTLIL::IdString("\\ABITS")).as_int();
+				int address = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\ADDR")), address_width);
+				int data_width = cell->parameters.at(RTLIL::IdString("\\WIDTH")).as_int();
+				int data = dump_sigspec(&cell->connections.at(RTLIL::IdString("\\DATA")), data_width);
+				str = cell->parameters.at(RTLIL::IdString("\\MEMID")).decode_string();
+				int mem = dump_memory(module->memories.at(RTLIL::IdString(str.c_str())));
+				++line_num;
+				if(polarity)
+					str = stringf("%d one 1", line_num);
+				else
+					str = stringf("%d zero 1", line_num);
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d eq 1 %d %d", line_num, clk, line_num-1);	
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d and 1 %d %d", line_num, line_num-1, enable);	
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d write %d %d %d %d %d", line_num, data_width, address_width, mem, address, data);	
+				fprintf(f, "%s\n", str.c_str());
+				++line_num;
+				str = stringf("%d acond %d %d %d %d %d", line_num, data_width, address_width, line_num-2/*enable*/, line_num-1, mem);	
+				fprintf(f, "%s\n", str.c_str());				
+				++line_num;
+				str = stringf("%d anext %d %d %d %d", line_num, data_width, address_width, mem, line_num-1);	
+				fprintf(f, "%s\n", str.c_str());				
+				line_ref[cell->name]=line_num;
+			}
+			curr_cell.clear();
+			return line_num;
+		}
+		else
+		{
+			return it->second;
+		}
+	}
+
+	RTLIL::SigSpec* get_cell_output(RTLIL::Cell* cell)
+	{
+		RTLIL::SigSpec *output_sig = nullptr;
+		if (cell->type == "$memrd")
+		{
+			output_sig = &cell->connections.at(RTLIL::IdString("\\DATA"));
+		}
+		else if(cell->type == "$memwr" || cell->type == "$assert")
+		{
+			//no output
+		}
+		else if(cell->type == "$dff" || cell->type == "$adff" || cell->type == "$dffsr")
+		{
+			output_sig = &cell->connections.at(RTLIL::IdString("\\Q"));
+		}
+		else 
+		{
+			output_sig = &cell->connections.at(RTLIL::IdString("\\Y"));
+		}
+		return output_sig;
+	}
+
+	void dump_property(RTLIL::Wire *wire)
+	{
+		int l = dump_wire(wire);
+		++line_num;
+		str = stringf("%d root 1 %d", line_num, l);
+		fprintf(f, "%s\n", str.c_str());
+	}
+
+	void dump()
+	{
+		fprintf(f, ";module %s\n", cstr(module->name));
+		
+		log("creating intermediate wires map\n");
+		//creating map of intermediate wires as output of some cell
+		for (auto it = module->cells.begin(); it != module->cells.end(); ++it)
+		{
+			RTLIL::Cell *cell = it->second;
+			RTLIL::SigSpec* output_sig = get_cell_output(cell);
+			if(output_sig==nullptr)
+				continue;
+			RTLIL::SigSpec s = sigmap(*output_sig);
+			output_sig = &s;
+			log(" - %s\n", cstr(it->second->type));
+			if (cell->type == "$memrd")
+			{
+				for(unsigned i=0; i<output_sig->chunks.size(); ++i)
+				{
+					RTLIL::Wire *w = output_sig->chunks[i].wire;
+					RTLIL::IdString wire_id = w->name;
+					inter_wire_map[wire_id].insert(WireInfo(cell->name,&output_sig->chunks[i]));
+				}
+			}
+			else if(cell->type == "$memwr")
+			{
+				continue;//nothing to do
+			}
+			else if(cell->type == "$dff" || cell->type == "$adff" || cell->type == "$dffsr")
+			{
+				RTLIL::IdString wire_id = output_sig->chunks[0].wire->name;
+				for(unsigned i=0; i<output_sig->chunks.size(); ++i)
+				{
+					RTLIL::Wire *w = output_sig->chunks[i].wire;
+					RTLIL::IdString wire_id = w->name;
+					inter_wire_map[wire_id].insert(WireInfo(cell->name,&output_sig->chunks[i]));
+					basic_wires[wire_id] = true;
+				}
+			}
+			else 
+			{
+				for(unsigned i=0; i<output_sig->chunks.size(); ++i)
+				{
+					RTLIL::Wire *w = output_sig->chunks[i].wire;
+					RTLIL::IdString wire_id = w->name;
+					inter_wire_map[wire_id].insert(WireInfo(cell->name,&output_sig->chunks[i]));
+				}
+			}
+		}
+		
+		log("writing input\n");
+		std::map<int, RTLIL::Wire*> inputs, outputs;
+		std::vector<RTLIL::Wire*> safety;
+		
+		for (auto &wire_it : module->wires) {
+			RTLIL::Wire *wire = wire_it.second;
+			if (wire->port_input)
+				inputs[wire->port_id] = wire;
+			if (wire->port_output) {
+				outputs[wire->port_id] = wire;
+				if (wire->name.find("safety") != std::string::npos )
+					safety.push_back(wire);
+			}
+		}
+
+		fprintf(f, ";inputs\n");
+		for (auto &it : inputs) {
+			RTLIL::Wire *wire = it.second;
+			dump_wire(wire);
+		}
+		fprintf(f, "\n");
+		
+		log("writing memories\n");
+		for(auto mem_it = module->memories.begin(); mem_it != module->memories.end(); ++mem_it)
+		{
+			dump_memory(mem_it->second);
+		}
+
+		log("writing output wires\n");
+		for (auto &it : outputs) {
+			RTLIL::Wire *wire = it.second;
+			dump_wire(wire);
+		}
+
+		log("writing cells\n");
+		for(auto cell_it = module->cells.begin(); cell_it != module->cells.end(); ++cell_it)
+		{
+			dump_cell(cell_it->second);	
+		}
+		
+		for(auto it: safety)
+			dump_property(it);
+
+		fprintf(f, "\n");
+		
+		log("writing outputs info\n");
+		fprintf(f, ";outputs\n");
+		for (auto &it : outputs) {
+			RTLIL::Wire *wire = it.second;
+			int l = dump_wire(wire);
+			fprintf(f, ";%d %s", l, cstr(wire->name));
+		}
+		fprintf(f, "\n");
+	}
+
+	static void dump(FILE *f, RTLIL::Module *module, RTLIL::Design *design, BtorDumperConfig &config)
+	{
+		BtorDumper dumper(f, module, design, &config);
+		dumper.dump();
+	}
+};
+
+struct BtorBackend : public Backend {
+	BtorBackend() : Backend("btor", "write design to BTOR file") { }
+	
+	virtual void help()
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    write_btor [filename]\n");
+		log("\n");
+		log("Write the current design to an BTOR file.\n");
+	}
+
+	virtual void execute(FILE *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design)
+	{
+		std::string top_module_name;
+		std::string buf_type, buf_in, buf_out;
+		std::string true_type, true_out;
+		std::string false_type, false_out;
+		BtorDumperConfig config;
+
+		log_header("Executing BTOR backend.\n");
+
+		size_t argidx=1;
+		extra_args(f, filename, args, argidx);
+		
+		if (top_module_name.empty())
+			for (auto & mod_it:design->modules)
+				if (mod_it.second->get_bool_attribute("\\top"))
+					top_module_name = mod_it.first;
+
+		fprintf(f, "; Generated by %s\n", yosys_version_str);
+		fprintf(f, ";  %s developed and maintained by Clifford Wolf <clifford@clifford.at>\n", yosys_version_str);
+		fprintf(f, "; BTOR Backend developed by Ahmed Irfan <irfan@fbk.eu> - Fondazione Bruno Kessler, Trento, Italy\n");
+		fprintf(f, ";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n");
+		
+		std::vector<RTLIL::Module*> mod_list;
+
+		for (auto module_it : design->modules)
+		{
+			RTLIL::Module *module = module_it.second;
+			if (module->get_bool_attribute("\\blackbox"))
+				continue;
+
+			if (module->processes.size() != 0)
+				log_error("Found unmapped processes in module %s: unmapped processes are not supported in BLIF backend!\n", RTLIL::id2cstr(module->name));
+
+			if (module->name == RTLIL::escape_id(top_module_name)) {
+				BtorDumper::dump(f, module, design, config);
+				top_module_name.clear();
+				continue;
+			}
+
+			mod_list.push_back(module);
+		}
+
+		if (!top_module_name.empty())
+			log_error("Can't find top module `%s'!\n", top_module_name.c_str());
+
+		for (auto module : mod_list)
+			BtorDumper::dump(f, module, design, config);
+	}
+} BtorBackend;
+
diff --git a/backends/btor/btor.ys b/backends/btor/btor.ys
new file mode 100644
index 000000000..20bce87e1
--- /dev/null
+++ b/backends/btor/btor.ys
@@ -0,0 +1,15 @@
+proc; 
+opt; opt_const -mux_undef; opt;
+rename -hide;;;
+#converting pmux to mux
+techmap -share_map pmux2mux.v;;
+memory -nomap;;
+#flatten design
+flatten;;
+#converting asyn memory write to syn memory
+memory_unpack; 
+#cell output to be a single wire
+splitnets -driver;
+setundef -zero -undriven;
+opt;;;
+
diff --git a/backends/btor/verilog2btor.sh b/backends/btor/verilog2btor.sh
new file mode 100755
index 000000000..a2f9ebc7e
--- /dev/null
+++ b/backends/btor/verilog2btor.sh
@@ -0,0 +1,35 @@
+#!/bin/sh
+
+#
+# Script to writing btor from verilog design
+#
+
+if [ "$#" -ne 3 ]; then
+  echo "Usage: $0 input.v output.btor top-module-name" >&2
+  exit 1
+fi
+if ! [ -e "$1" ]; then
+  echo "$1 not found" >&2
+  exit 1
+fi
+
+FULL_PATH=$(readlink -f $1)
+DIR=$(dirname $FULL_PATH)
+
+./yosys -q -p "
+read_verilog $1; 
+hierarchy -top $3; 
+hierarchy -libdir $DIR; 
+hierarchy -check; 
+proc; 
+opt; opt_const -mux_undef; opt;
+rename -hide;;;
+techmap -share_map pmux2mux.v;;
+memory -nomap;;
+flatten;;
+memory_unpack; 
+splitnets -driver;
+setundef -zero -undriven;
+opt;;;
+write_btor $2;"
+
diff --git a/manual/make.sh b/manual/make.sh
old mode 100644
new mode 100755