initial import

3 files changed, 947 insertions, 0 deletions

diff --git a/backends/verilog/Makefile.inc b/backends/verilog/Makefile.inc
new file mode 100644
index 000000000..c2dffef7a
--- /dev/null
+++ b/backends/verilog/Makefile.inc
@@ -0,0 +1,3 @@
+
+OBJS += backends/verilog/verilog_backend.o
+
diff --git a/backends/verilog/verilog_backend.cc b/backends/verilog/verilog_backend.cc
new file mode 100644
index 000000000..d79908006
--- /dev/null
+++ b/backends/verilog/verilog_backend.cc
@@ -0,0 +1,905 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *  
+ *  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.
+ *
+ *  ---
+ *
+ *  A simple and straightforward verilog backend.
+ *
+ *  Note that RTLIL processes can't always be mapped easily to a Verilog
+ *  process. Therefore this frontend should only be used to export a
+ *  Verilog netlist (i.e. after the "proc" pass has converted all processes
+ *  to logic networks and registers).
+ *
+ */
+
+#include "verilog_backend.h"
+#include "kernel/register.h"
+#include "kernel/celltypes.h"
+#include "kernel/log.h"
+#include <assert.h>
+#include <string>
+#include <sstream>
+#include <set>
+#include <map>
+
+namespace {
+
+bool norename, noattr, attr2comment, noexpr;
+int auto_name_counter, auto_name_offset, auto_name_digits;
+std::map<std::string, int> auto_name_map;
+
+std::set<std::string> reg_wires;
+
+CellTypes reg_ct;
+RTLIL::Module *active_module;
+
+void reset_auto_counter_id(const std::string &id, bool may_rename)
+{
+	const char *str = id.c_str();
+
+	if (*str == '$' && may_rename && !norename)
+		auto_name_map[id] = auto_name_counter++;
+
+	if (str[0] != '_' && str[1] != 0)
+		return;
+	for (int i = 0; str[i] != 0; i++) {
+		if (str[i] == '_')
+			continue;
+		if (str[i] < '0' || str[i] > '9')
+			return;
+	}
+
+	int num = atoi(str+1);
+	if (num >= auto_name_offset)
+		auto_name_offset = num + 1;
+}
+
+void reset_auto_counter(RTLIL::Module *module)
+{
+	auto_name_map.clear();
+	auto_name_counter = 0;
+	auto_name_offset = 0;
+
+	reset_auto_counter_id(module->name, false);
+
+	for (auto it = module->wires.begin(); it != module->wires.end(); it++)
+		reset_auto_counter_id(it->second->name, true);
+
+	for (auto it = module->cells.begin(); it != module->cells.end(); it++) {
+		reset_auto_counter_id(it->second->name, true);
+		reset_auto_counter_id(it->second->type, false);
+	}
+
+	for (auto it = module->processes.begin(); it != module->processes.end(); it++)
+		reset_auto_counter_id(it->second->name, false);
+
+	auto_name_digits = 1;
+	for (size_t i = 10; i < auto_name_offset + auto_name_map.size(); i = i*10)
+		auto_name_digits++;
+
+	for (auto it = auto_name_map.begin(); it != auto_name_map.end(); it++)
+		log("  renaming `%s' to `_%0*d_'.\n", it->first.c_str(), auto_name_digits, auto_name_offset + it->second);
+}
+
+std::string id(std::string internal_id, bool may_rename = true)
+{
+	const char *str = internal_id.c_str();
+	bool do_escape = false;
+
+	if (may_rename && auto_name_map.count(internal_id) != 0) {
+		char buffer[100];
+		snprintf(buffer, 100, "_%0*d_", auto_name_digits, auto_name_offset + auto_name_map[internal_id]);
+		return std::string(buffer);
+	}
+
+	if (*str == '\\')
+		str++;
+
+	if ('0' <= *str && *str <= '9')
+		do_escape = true;
+
+	for (int i = 0; str[i]; i++)
+	{
+		if ('0' <= str[i] && str[i] <= '9')
+			continue;
+		if ('a' <= str[i] && str[i] <= 'z')
+			continue;
+		if ('A' <= str[i] && str[i] <= 'Z')
+			continue;
+		if (str[i] == '_')
+			continue;
+		do_escape = true;
+		break;
+	}
+
+	if (do_escape)
+		return "\\" + std::string(str) + " ";
+	return std::string(str);
+}
+
+bool is_reg_wire(RTLIL::SigSpec sig, std::string &reg_name)
+{
+	sig.optimize();
+	if (sig.chunks.size() != 1 || sig.chunks[0].wire == NULL)
+		return false;
+	if (reg_wires.count(sig.chunks[0].wire->name) == 0)
+		return false;
+	reg_name = id(sig.chunks[0].wire->name);
+	if (sig.width != sig.chunks[0].wire->width)
+		if (sig.width == 1)
+			reg_name += stringf("[%d]", sig.chunks[0].wire->start_offset +  sig.chunks[0].offset);
+		else
+			reg_name += stringf("[%d]", sig.chunks[0].wire->start_offset +  sig.chunks[0].offset + sig.chunks[0].width - 1,
+					sig.chunks[0].wire->start_offset +  sig.chunks[0].offset);
+	return true;
+}
+
+void dump_const(FILE *f, RTLIL::Const &data, int width = -1, int offset = 0, bool no_decimal = false)
+{
+	if (width < 0)
+		width = data.bits.size() - offset;
+	if (data.str.empty() || width != (int)data.bits.size()) {
+		if (width == 32 && !no_decimal) {
+			uint32_t val = 0;
+			for (int i = offset+width-1; i >= offset; i--) {
+				assert(i < (int)data.bits.size());
+				if (data.bits[i] != RTLIL::S0 && data.bits[i] != RTLIL::S1)
+					goto dump_bits;
+				if (data.bits[i] == RTLIL::S1)
+					val |= 1 << (i - offset);
+			}
+			fprintf(f, "%d", (int)val);
+		} else {
+	dump_bits:
+			fprintf(f, "%d'b", width);
+			for (int i = offset+width-1; i >= offset; i--) {
+				assert(i < (int)data.bits.size());
+				switch (data.bits[i]) {
+				case RTLIL::S0: fprintf(f, "0"); break;
+				case RTLIL::S1: fprintf(f, "1"); break;
+				case RTLIL::Sx: fprintf(f, "x"); break;
+				case RTLIL::Sz: fprintf(f, "z"); break;
+				case RTLIL::Sa: fprintf(f, "z"); break;
+				case RTLIL::Sm: log_error("Found marker state in final netlist.");
+				}
+			}
+		}
+	} else {
+		fprintf(f, "\"");
+		for (size_t i = 0; i < data.str.size(); i++) {
+			if (data.str[i] == '\n')
+				fprintf(f, "\\n");
+			else if (data.str[i] == '\t')
+				fprintf(f, "\\t");
+			else if (data.str[i] < 32)
+				fprintf(f, "\\%03o", data.str[i]);
+			else if (data.str[i] == '"')
+				fprintf(f, "\\\"");
+			else
+				fputc(data.str[i], f);
+		}
+		fprintf(f, "\"");
+	}
+}
+
+void dump_sigchunk(FILE *f, RTLIL::SigChunk &chunk, bool no_decimal = false)
+{
+	if (chunk.wire == NULL) {
+		dump_const(f, chunk.data, chunk.width, chunk.offset, no_decimal);
+	} else {
+		if (chunk.width == chunk.wire->width && chunk.offset == 0)
+			fprintf(f, "%s", id(chunk.wire->name).c_str());
+		else if (chunk.width == 1)
+			fprintf(f, "%s[%d]", id(chunk.wire->name).c_str(), chunk.offset + chunk.wire->start_offset);
+		else
+			fprintf(f, "%s[%d:%d]", id(chunk.wire->name).c_str(),
+					chunk.offset + chunk.wire->start_offset + chunk.width - 1,
+					chunk.offset + chunk.wire->start_offset);
+	}
+}
+
+void dump_sigspec(FILE *f, RTLIL::SigSpec &sig)
+{
+	if (sig.chunks.size() == 1) {
+		dump_sigchunk(f, sig.chunks[0]);
+	} else {
+		fprintf(f, "{ ");
+		for (auto it = sig.chunks.rbegin(); it != sig.chunks.rend(); it++) {
+			if (it != sig.chunks.rbegin())
+				fprintf(f, ", ");
+			dump_sigchunk(f, *it, true);
+		}
+		fprintf(f, " }");
+	}
+}
+
+void dump_attributes(FILE *f, std::string indent, std::map<RTLIL::IdString, RTLIL::Const> &attributes, char term = '\n')
+{
+	if (noattr)
+		return;
+	for (auto it = attributes.begin(); it != attributes.end(); it++) {
+		fprintf(f, "%s" "%s %s", indent.c_str(), attr2comment ? "/*" : "(*", id(it->first).c_str());
+		if (it->second.bits.size() > 0) {
+			fprintf(f, " = ");
+			dump_const(f, it->second);
+		}
+		fprintf(f, " %s%c", attr2comment ? "*/" : "*)", term);
+	}
+}
+
+void dump_wire(FILE *f, std::string indent, RTLIL::Wire *wire)
+{
+	dump_attributes(f, indent, wire->attributes);
+	if (wire->port_input && !wire->port_output)
+		fprintf(f, "%s" "input %s", indent.c_str(), reg_wires.count(wire->name) ? "reg " : "");
+	else if (!wire->port_input && wire->port_output)
+		fprintf(f, "%s" "output %s", indent.c_str(), reg_wires.count(wire->name) ? "reg " : "");
+	else if (wire->port_input && wire->port_output)
+		fprintf(f, "%s" "inout %s", indent.c_str(), reg_wires.count(wire->name) ? "reg " : "");
+	else
+		fprintf(f, "%s" "%s ", indent.c_str(), reg_wires.count(wire->name) ? "reg" : "wire");
+	if (wire->width != 1)
+		fprintf(f, "[%d:%d] ", wire->width - 1 + wire->start_offset, wire->start_offset);
+	fprintf(f, "%s;\n", id(wire->name).c_str());
+}
+
+void dump_memory(FILE *f, std::string indent, RTLIL::Memory *memory)
+{
+	dump_attributes(f, indent, memory->attributes);
+	fprintf(f, "%s" "reg [%d:0] %s [%d:0];\n", indent.c_str(), memory->width-1, id(memory->name).c_str(), memory->size-1);
+}
+
+void dump_cell_expr_port(FILE *f, RTLIL::Cell *cell, std::string port, bool gen_signed = true)
+{
+	if (gen_signed && cell->parameters.count("\\" + port + "_SIGNED") > 0 && cell->parameters["\\" + port + "_SIGNED"].as_bool()) {
+		fprintf(f, "$signed(");
+		dump_sigspec(f, cell->connections["\\" + port]);
+		fprintf(f, ")");
+	} else
+		dump_sigspec(f, cell->connections["\\" + port]);
+}
+
+std::string cellname(RTLIL::Cell *cell)
+{
+	if (!norename && cell->name[0] == '$' && reg_ct.cell_known(cell->type) && cell->connections.count("\\Q") > 0)
+	{
+		RTLIL::SigSpec sig = cell->connections["\\Q"];
+		if (sig.width != 1 || sig.is_fully_const())
+			goto no_special_reg_name;
+
+		sig.optimize();
+		RTLIL::Wire *wire = sig.chunks[0].wire;
+
+		if (wire->name[0] != '\\')
+			goto no_special_reg_name;
+
+		std::string cell_name = wire->name;
+
+		size_t pos = cell_name.find('[');
+		if (pos != std::string::npos)
+			cell_name = cell_name.substr(0, pos) + "_reg" + cell_name.substr(pos);
+		else
+			cell_name = cell_name + "_reg";
+
+		if (wire->width != 1)
+			cell_name += stringf("[%d]", wire->start_offset + sig.chunks[0].offset);
+
+		if (active_module && active_module->count_id(cell_name) > 0)
+				goto no_special_reg_name;
+
+		return id(cell_name);
+	}
+	else
+	{
+no_special_reg_name:
+		return id(cell->name).c_str();
+	}
+}
+
+void dump_cell_expr_uniop(FILE *f, std::string indent, RTLIL::Cell *cell, std::string op)
+{
+	fprintf(f, "%s" "assign ", indent.c_str());
+	dump_sigspec(f, cell->connections["\\Y"]);
+	fprintf(f, " = %s ", op.c_str());
+	dump_attributes(f, "", cell->attributes, ' ');
+	dump_cell_expr_port(f, cell, "A", true);
+	fprintf(f, ";\n");
+}
+
+void dump_cell_expr_binop(FILE *f, std::string indent, RTLIL::Cell *cell, std::string op)
+{
+	fprintf(f, "%s" "assign ", indent.c_str());
+	dump_sigspec(f, cell->connections["\\Y"]);
+	fprintf(f, " = ");
+	dump_cell_expr_port(f, cell, "A", true);
+	fprintf(f, " %s ", op.c_str());
+	dump_attributes(f, "", cell->attributes, ' ');
+	dump_cell_expr_port(f, cell, "B", true);
+	fprintf(f, ";\n");
+}
+
+bool dump_cell_expr(FILE *f, std::string indent, RTLIL::Cell *cell)
+{
+	if (cell->type == "$_INV_") {
+		fprintf(f, "%s" "assign ", indent.c_str());
+		dump_sigspec(f, cell->connections["\\Y"]);
+		fprintf(f, " = ");
+		fprintf(f, "~");
+		dump_attributes(f, "", cell->attributes, ' ');
+		dump_cell_expr_port(f, cell, "A", false);
+		fprintf(f, ";\n");
+		return true;
+	}
+
+	if (cell->type == "$_AND_" || cell->type == "$_OR_" || cell->type == "$_XOR_") {
+		fprintf(f, "%s" "assign ", indent.c_str());
+		dump_sigspec(f, cell->connections["\\Y"]);
+		fprintf(f, " = ");
+		dump_cell_expr_port(f, cell, "A", false);
+		fprintf(f, " ");
+		if (cell->type == "$_AND_")
+			fprintf(f, "&");
+		if (cell->type == "$_OR_")
+			fprintf(f, "|");
+		if (cell->type == "$_XOR_")
+			fprintf(f, "^");
+		dump_attributes(f, "", cell->attributes, ' ');
+		fprintf(f, " ");
+		dump_cell_expr_port(f, cell, "B", false);
+		fprintf(f, ";\n");
+		return true;
+	}
+
+	if (cell->type == "$_MUX_") {
+		fprintf(f, "%s" "assign ", indent.c_str());
+		dump_sigspec(f, cell->connections["\\Y"]);
+		fprintf(f, " = ");
+		dump_cell_expr_port(f, cell, "S", false);
+		fprintf(f, " ? ");
+		dump_attributes(f, "", cell->attributes, ' ');
+		dump_cell_expr_port(f, cell, "B", false);
+		fprintf(f, " : ");
+		dump_cell_expr_port(f, cell, "A", false);
+		fprintf(f, ";\n");
+		return true;
+	}
+
+	if (cell->type.substr(0, 6) == "$_DFF_")
+	{
+		std::string reg_name = cellname(cell);
+		bool out_is_reg_wire = is_reg_wire(cell->connections["\\Q"], reg_name);
+
+		if (!out_is_reg_wire)
+			fprintf(f, "%s" "reg %s;\n", indent.c_str(), reg_name.c_str());
+
+		dump_attributes(f, indent, cell->attributes);
+		fprintf(f, "%s" "always @(%sedge ", indent.c_str(), cell->type[6] == 'P' ? "pos" : "neg");
+		dump_sigspec(f, cell->connections["\\C"]);
+		if (cell->type[7] != '_') {
+			fprintf(f, " or %sedge ", cell->type[7] == 'P' ? "pos" : "neg");
+			dump_sigspec(f, cell->connections["\\R"]);
+		}
+		fprintf(f, ")\n");
+
+		if (cell->type[7] != '_') {
+			fprintf(f, "%s" "  if (%s", indent.c_str(), cell->type[7] == 'P' ? "" : "!");
+			dump_sigspec(f, cell->connections["\\R"]);
+			fprintf(f, ")\n");
+			fprintf(f, "%s" "    %s <= %c;\n", indent.c_str(), reg_name.c_str(), cell->type[8]);
+			fprintf(f, "%s" "  else\n", indent.c_str());
+		}
+
+		fprintf(f, "%s" "    %s <= ", indent.c_str(), reg_name.c_str());
+		dump_cell_expr_port(f, cell, "D", false);
+		fprintf(f, ";\n");
+
+		if (!out_is_reg_wire) {
+			fprintf(f, "%s" "assign ", indent.c_str());
+			dump_sigspec(f, cell->connections["\\Q"]);
+			fprintf(f, " = %s;\n", reg_name.c_str());
+		}
+
+		return true;
+	}
+
+#define HANDLE_UNIOP(_type, _operator) \
+	if (cell->type ==_type) { dump_cell_expr_uniop(f, indent, cell, _operator); return true; }
+#define HANDLE_BINOP(_type, _operator) \
+	if (cell->type ==_type) { dump_cell_expr_binop(f, indent, cell, _operator); return true; }
+
+	HANDLE_UNIOP("$not", "~")
+	HANDLE_UNIOP("$pos", "+")
+	HANDLE_UNIOP("$neg", "-")
+
+	HANDLE_BINOP("$and",  "&")
+	HANDLE_BINOP("$or",   "|")
+	HANDLE_BINOP("$xor",  "^")
+	HANDLE_BINOP("$xnor", "~^")
+
+	HANDLE_UNIOP("$reduce_and",  "&")
+	HANDLE_UNIOP("$reduce_or",   "|")
+	HANDLE_UNIOP("$reduce_xor",  "^")
+	HANDLE_UNIOP("$reduce_xnor", "~^")
+	HANDLE_UNIOP("$reduce_bool", "|")
+
+	HANDLE_BINOP("$shl",  "<<")
+	HANDLE_BINOP("$shr",  ">>")
+	HANDLE_BINOP("$sshl", "<<<")
+	HANDLE_BINOP("$sshr", ">>>")
+
+	HANDLE_BINOP("$lt", "<")
+	HANDLE_BINOP("$le", "<=")
+	HANDLE_BINOP("$eq", "==")
+	HANDLE_BINOP("$ne", "!=")
+	HANDLE_BINOP("$ge", ">=")
+	HANDLE_BINOP("$gt", ">")
+
+	HANDLE_BINOP("$add", "+")
+	HANDLE_BINOP("$sub", "-")
+	HANDLE_BINOP("$mul", "*")
+	HANDLE_BINOP("$div", "/")
+	HANDLE_BINOP("$mod", "%")
+	HANDLE_BINOP("$pow", "**")
+
+	HANDLE_UNIOP("$logic_not", "!")
+	HANDLE_BINOP("$logic_and", "&&")
+	HANDLE_BINOP("$logic_or",  "||")
+
+#undef HANDLE_UNIOP
+#undef HANDLE_BINOP
+
+	if (cell->type == "$mux" || cell->type == "$pmux" || cell->type == "$pmux_safe")
+	{
+		int width = cell->parameters["\\WIDTH"].as_int();
+		int s_width = cell->connections["\\S"].width;
+		std::string reg_name = cellname(cell);
+		fprintf(f, "%s" "reg [%d:0] %s;\n", indent.c_str(), width-1, reg_name.c_str());
+
+		dump_attributes(f, indent, cell->attributes);
+		if (!noattr)
+			fprintf(f, "%s" "(* parallel_case *)\n", indent.c_str());
+		fprintf(f, "%s" "always @*\n", indent.c_str());
+		fprintf(f, "%s" "  casez (", indent.c_str());
+		dump_sigspec(f, cell->connections["\\S"]);
+		fprintf(f, noattr ? ") // synopsys parallel_case\n" : ")\n");
+
+		for (int i = 0; i < s_width; i++)
+		{
+			fprintf(f, "%s" "    %d'b", indent.c_str(), s_width);
+
+			for (int j = s_width-1; j >= 0; j--)
+				fprintf(f, "%c", j == i ? '1' : cell->type == "$pmux_safe" ? '0' : '?');
+
+			fprintf(f, ":\n");
+			fprintf(f, "%s" "      %s = ", indent.c_str(), reg_name.c_str());
+
+			RTLIL::SigSpec s = cell->connections["\\B"].extract(i * width, width);
+			dump_sigspec(f, s);
+			fprintf(f, ";\n");
+		}
+
+		fprintf(f, "%s" "    default:\n", indent.c_str());
+		fprintf(f, "%s" "      %s = ", indent.c_str(), reg_name.c_str());
+		dump_sigspec(f, cell->connections["\\A"]);
+		fprintf(f, ";\n");
+
+		fprintf(f, "%s" "  endcase\n", indent.c_str());
+		fprintf(f, "%s" "assign ", indent.c_str());
+		dump_sigspec(f, cell->connections["\\Y"]);
+		fprintf(f, " = %s;\n", reg_name.c_str());
+		return true;
+	}
+
+	if (cell->type == "$dff" || cell->type == "$adff")
+	{
+		RTLIL::SigSpec sig_clk, sig_arst, val_arst;
+		bool pol_clk, pol_arst = false;
+
+		sig_clk = cell->connections["\\CLK"];
+		pol_clk = cell->parameters["\\CLK_POLARITY"].as_bool();
+
+		if (cell->type == "$adff") {
+			sig_arst = cell->connections["\\ARST"];
+			pol_arst = cell->parameters["\\ARST_POLARITY"].as_bool();
+			val_arst = RTLIL::SigSpec(cell->parameters["\\ARST_VALUE"]);
+		}
+
+		std::string reg_name = cellname(cell);
+		bool out_is_reg_wire = is_reg_wire(cell->connections["\\Q"], reg_name);
+
+		if (!out_is_reg_wire)
+			fprintf(f, "%s" "reg [%d:0] %s;\n", indent.c_str(), cell->parameters["\\WIDTH"].as_int()-1, reg_name.c_str());
+
+		fprintf(f, "%s" "always @(%sedge ", indent.c_str(), pol_clk ? "pos" : "neg");
+		dump_sigspec(f, sig_clk);
+		if (cell->type == "$adff") {
+			fprintf(f, " or %sedge ", pol_arst ? "pos" : "neg");
+			dump_sigspec(f, sig_arst);
+		}
+		fprintf(f, ")\n");
+
+		if (cell->type == "$adff") {
+			fprintf(f, "%s" "  if (%s", indent.c_str(), pol_arst ? "" : "!");
+			dump_sigspec(f, sig_arst);
+			fprintf(f, ")\n");
+			fprintf(f, "%s" "    %s <= ", indent.c_str(), reg_name.c_str());
+			dump_sigspec(f, val_arst);
+			fprintf(f, ";\n");
+			fprintf(f, "%s" "  else\n", indent.c_str());
+		}
+
+		fprintf(f, "%s" "    %s <= ", indent.c_str(), reg_name.c_str());
+		dump_cell_expr_port(f, cell, "D", false);
+		fprintf(f, ";\n");
+
+		if (!out_is_reg_wire) {
+			fprintf(f, "%s" "assign ", indent.c_str());
+			dump_sigspec(f, cell->connections["\\Q"]);
+			fprintf(f, " = %s;\n", reg_name.c_str());
+		}
+
+		return true;
+	}
+
+	// FIXME: $memrd, $memwr, $mem, $fsm
+
+	return false;
+}
+
+void dump_cell(FILE *f, std::string indent, RTLIL::Cell *cell)
+{
+	if (cell->type[0] == '$' && !noexpr) {
+		if (dump_cell_expr(f, indent, cell))
+			return;
+	}
+
+	dump_attributes(f, indent, cell->attributes);
+	fprintf(f, "%s" "%s", indent.c_str(), id(cell->type, false).c_str());
+
+	if (cell->parameters.size() > 0) {
+		fprintf(f, " #(");
+		for (auto it = cell->parameters.begin(); it != cell->parameters.end(); it++) {
+			if (it != cell->parameters.begin())
+				fprintf(f, ",");
+			fprintf(f, "\n%s  .%s(", indent.c_str(), id(it->first).c_str());
+			dump_const(f, it->second);
+			fprintf(f, ")");
+		}
+		fprintf(f, "\n%s" ")", indent.c_str());
+	}
+
+	std::string cell_name = cellname(cell);
+	if (cell_name != id(cell->name))
+		fprintf(f, " %s /* %s */ (", cell_name.c_str(), id(cell->name).c_str());
+	else
+		fprintf(f, " %s (", cell_name.c_str());
+
+	bool first_arg = true;
+	std::set<std::string> numbered_ports;
+	for (int i = 1; true; i++) {
+		char str[16];
+		snprintf(str, 16, "$%d", i);
+		for (auto it = cell->connections.begin(); it != cell->connections.end(); it++) {
+			if (it->first != str)
+				continue;
+			if (!first_arg)
+				fprintf(f, ",");
+			first_arg = false;
+			fprintf(f, "\n%s  ", indent.c_str());
+			dump_sigspec(f, it->second);
+			numbered_ports.insert(it->first);
+			goto found_numbered_port;
+		}
+		break;
+	found_numbered_port:;
+	}
+	for (auto it = cell->connections.begin(); it != cell->connections.end(); it++) {
+		if (numbered_ports.count(it->first))
+			continue;
+		if (!first_arg)
+			fprintf(f, ",");
+		first_arg = false;
+		fprintf(f, "\n%s  .%s(", indent.c_str(), id(it->first).c_str());
+		if (it->second.width > 0)
+			dump_sigspec(f, it->second);
+		fprintf(f, ")");
+	}
+	fprintf(f, "\n%s" ");\n", indent.c_str());
+}
+
+void dump_conn(FILE *f, std::string indent, RTLIL::SigSpec &left, RTLIL::SigSpec &right)
+{
+	fprintf(f, "%s" "assign ", indent.c_str());
+	dump_sigspec(f, left);
+	fprintf(f, " = ");
+	dump_sigspec(f, right);
+	fprintf(f, ";\n");
+}
+
+void dump_proc_switch(FILE *f, std::string indent, RTLIL::SwitchRule *sw);
+
+void dump_case_body(FILE *f, std::string indent, RTLIL::CaseRule *cs, bool omit_trailing_begin = false)
+{
+	int number_of_stmts = cs->switches.size() + cs->actions.size();
+
+	if (!omit_trailing_begin && number_of_stmts >= 2)
+		fprintf(f, "%s" "begin\n", indent.c_str());
+
+	for (auto it = cs->actions.begin(); it != cs->actions.end(); it++) {
+		if (it->first.width == 0)
+			continue;
+		fprintf(f, "%s  ", indent.c_str());
+		dump_sigspec(f, it->first);
+		fprintf(f, " = ");
+		dump_sigspec(f, it->second);
+		fprintf(f, ";\n");
+	}
+
+	for (auto it = cs->switches.begin(); it != cs->switches.end(); it++)
+		dump_proc_switch(f, indent + "  ", *it);
+
+	if (!omit_trailing_begin && number_of_stmts == 0)
+		fprintf(f, "%s  /* empty */;\n", indent.c_str());
+
+	if (omit_trailing_begin || number_of_stmts >= 2)
+		fprintf(f, "%s" "end\n", indent.c_str());
+}
+
+void dump_proc_switch(FILE *f, std::string indent, RTLIL::SwitchRule *sw)
+{
+	if (sw->signal.width == 0) {
+		fprintf(f, "%s" "begin\n", indent.c_str());
+		for (auto it = sw->cases.begin(); it != sw->cases.end(); it++) {
+			if ((*it)->compare.size() == 0)
+				dump_case_body(f, indent + "  ", *it);
+		}
+		fprintf(f, "%s" "end\n", indent.c_str());
+		return;
+	}
+
+	fprintf(f, "%s" "casez (", indent.c_str());
+	dump_sigspec(f, sw->signal);
+	fprintf(f, ")\n");
+
+	for (auto it = sw->cases.begin(); it != sw->cases.end(); it++) {
+		fprintf(f, "%s  ", indent.c_str());
+		if ((*it)->compare.size() == 0)
+			fprintf(f, "default");
+		else {
+			for (size_t i = 0; i < (*it)->compare.size(); i++) {
+				if (i > 0)
+					fprintf(f, ", ");
+				dump_sigspec(f, (*it)->compare[i]);
+			}
+		}
+		fprintf(f, ":\n");
+		dump_case_body(f, indent + "    ", *it);
+	}
+
+	fprintf(f, "%s" "endcase\n", indent.c_str());
+}
+
+void case_body_find_regs(RTLIL::CaseRule *cs)
+{
+	for (auto it = cs->switches.begin(); it != cs->switches.end(); it++)
+	for (auto it2 = (*it)->cases.begin(); it2 != (*it)->cases.end(); it2++)
+		case_body_find_regs(*it2);
+
+	for (auto it = cs->actions.begin(); it != cs->actions.end(); it++) {
+		for (size_t i = 0; i < it->first.chunks.size(); i++)
+			if (it->first.chunks[i].wire)
+				reg_wires.insert(it->first.chunks[i].wire->name);
+	}
+}
+
+void dump_process(FILE *f, std::string indent, RTLIL::Process *proc, bool find_regs = false)
+{
+	if (find_regs) {
+		case_body_find_regs(&proc->root_case);
+		for (auto it = proc->syncs.begin(); it != proc->syncs.end(); it++)
+		for (auto it2 = (*it)->actions.begin(); it2 != (*it)->actions.end(); it2++) {
+			for (size_t i = 0; i < it2->first.chunks.size(); i++)
+				if (it2->first.chunks[i].wire)
+					reg_wires.insert(it2->first.chunks[i].wire->name);
+		}
+		return;
+	}
+
+	fprintf(f, "%s" "always @* begin\n", indent.c_str());
+	dump_case_body(f, indent, &proc->root_case, true);
+
+	std::string backup_indent = indent;
+
+	for (size_t i = 0; i < proc->syncs.size(); i++)
+	{
+		RTLIL::SyncRule *sync = proc->syncs[i];
+		indent = backup_indent;
+
+		if (sync->type == RTLIL::STa) {
+			fprintf(f, "%s" "always @* begin\n", indent.c_str());
+		} else {
+			fprintf(f, "%s" "always @(", indent.c_str());
+			if (sync->type == RTLIL::STp || sync->type == RTLIL::ST1)
+				fprintf(f, "posedge ");
+			if (sync->type == RTLIL::STn || sync->type == RTLIL::ST0)
+				fprintf(f, "negedge ");
+			dump_sigspec(f, sync->signal);
+			fprintf(f, ") begin\n");
+		}
+		std::string ends = indent + "end\n";
+		indent += "  ";
+
+		if (sync->type == RTLIL::ST0 || sync->type == RTLIL::ST1) {
+			fprintf(f, "%s" "if (%s", indent.c_str(), sync->type == RTLIL::ST0 ? "!" : "");
+			dump_sigspec(f, sync->signal);
+			fprintf(f, ") begin\n");
+			ends = indent + "end\n" + ends;
+			indent += "  ";
+		}
+
+		if (sync->type == RTLIL::STp || sync->type == RTLIL::STn) {
+			for (size_t j = 0; j < proc->syncs.size(); j++) {
+				RTLIL::SyncRule *sync2 = proc->syncs[j];
+				if (sync2->type == RTLIL::ST0 || sync2->type == RTLIL::ST1) {
+					fprintf(f, "%s" "if (%s", indent.c_str(), sync2->type == RTLIL::ST1 ? "!" : "");
+					dump_sigspec(f, sync2->signal);
+					fprintf(f, ") begin\n");
+					ends = indent + "end\n" + ends;
+					indent += "  ";
+				}
+			}
+		}
+
+		for (auto it = sync->actions.begin(); it != sync->actions.end(); it++) {
+			if (it->first.width == 0)
+				continue;
+			fprintf(f, "%s  ", indent.c_str());
+			dump_sigspec(f, it->first);
+			fprintf(f, " <= ");
+			dump_sigspec(f, it->second);
+			fprintf(f, ";\n");
+		}
+
+		fprintf(f, "%s", ends.c_str());
+	}
+}
+
+void dump_module(FILE *f, std::string indent, RTLIL::Module *module)
+{
+	reg_wires.clear();
+	reset_auto_counter(module);
+	active_module = module;
+
+	for (auto it = module->processes.begin(); it != module->processes.end(); it++)
+		dump_process(f, indent + "  ", it->second, true);
+
+	if (!noexpr)
+	{
+		std::set<std::pair<RTLIL::Wire*,int>> reg_bits;
+		for (auto &it : module->cells)
+		{
+			RTLIL::Cell *cell = it.second;
+			if (!reg_ct.cell_known(cell->type) || cell->connections.count("\\Q") == 0)
+				continue;
+
+			RTLIL::SigSpec sig = cell->connections["\\Q"];
+			sig.optimize();
+
+			if (sig.chunks.size() == 1 && sig.chunks[0].wire)
+				for (int i = 0; i < sig.chunks[0].width; i++)
+					reg_bits.insert(std::pair<RTLIL::Wire*,int>(sig.chunks[0].wire, sig.chunks[0].offset+i));
+		}
+		for (auto &it : module->wires)
+		{
+			RTLIL::Wire *wire = it.second;
+			for (int i = 0; i < wire->width; i++)
+				if (reg_bits.count(std::pair<RTLIL::Wire*,int>(wire, i)) == 0)
+					goto this_wire_aint_reg;
+			reg_wires.insert(wire->name);
+		this_wire_aint_reg:;
+		}
+	}
+
+	dump_attributes(f, indent, module->attributes);
+	fprintf(f, "%s" "module %s(", indent.c_str(), id(module->name, false).c_str());
+	bool keep_running = true;
+	for (int port_id = 1; keep_running; port_id++) {
+		keep_running = false;
+		for (auto it = module->wires.begin(); it != module->wires.end(); it++) {
+			RTLIL::Wire *wire = it->second;
+			if (wire->port_id == port_id) {
+				if (port_id != 1)
+					fprintf(f, ", ");
+				fprintf(f, "%s", id(wire->name).c_str());
+				keep_running = true;
+				continue;
+			}
+		}
+	}
+	fprintf(f, ");\n");
+
+	for (auto it = module->wires.begin(); it != module->wires.end(); it++)
+		dump_wire(f, indent + "  ", it->second);
+
+	for (auto it = module->memories.begin(); it != module->memories.end(); it++)
+		dump_memory(f, indent + "  ", it->second);
+
+	for (auto it = module->cells.begin(); it != module->cells.end(); it++)
+		dump_cell(f, indent + "  ", it->second);
+
+	for (auto it = module->processes.begin(); it != module->processes.end(); it++)
+		dump_process(f, indent + "  ", it->second);
+
+	for (auto it = module->connections.begin(); it != module->connections.end(); it++)
+		dump_conn(f, indent + "  ", it->first, it->second);
+
+	fprintf(f, "%s" "endmodule\n", indent.c_str());
+	active_module = NULL;
+}
+
+} /* namespace */
+
+struct VerilogBackend : public Backend {
+	VerilogBackend() : Backend("verilog") { }
+	virtual void execute(FILE *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design)
+	{
+		log_header("Executing Verilog backend.\n");
+
+		norename = false;
+		noattr = false;
+		attr2comment = false;
+		noexpr = false;
+
+		reg_ct.clear();
+		reg_ct.setup_stdcells_mem();
+		reg_ct.cell_types.insert("$dff");
+		reg_ct.cell_types.insert("$adff");
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			std::string arg = args[argidx];
+			if (arg == "-norename") {
+				norename = true;
+				continue;
+			}
+			if (arg == "-noattr") {
+				noattr = true;
+				continue;
+			}
+			if (arg == "-attr2comment") {
+				attr2comment = true;
+				continue;
+			}
+			if (arg == "-noexpr") {
+				noexpr = true;
+				continue;
+			}
+			break;
+		}
+		extra_args(f, filename, args, argidx);
+
+		for (auto it = design->modules.begin(); it != design->modules.end(); it++) {
+			log("Dumping module `%s'.\n", it->first.c_str());
+			if (it != design->modules.begin())
+				fprintf(f, "\n");
+			dump_module(f, "", it->second);
+		}
+
+		reg_ct.clear();
+	}
+} VerilogBackend;
+
diff --git a/backends/verilog/verilog_backend.h b/backends/verilog/verilog_backend.h
new file mode 100644
index 000000000..c40830ef2
--- /dev/null
+++ b/backends/verilog/verilog_backend.h
@@ -0,0 +1,39 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *  
+ *  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.
+ *
+ *  ---
+ *
+ *  A simple and straightforward verilog backend.
+ *
+ *  Note that RTLIL processes can't always be mapped easily to a Verilog
+ *  process. Therefore this frontend should only be used to export a
+ *  Verilog netlist (i.e. after the "proc" pass has converted all processes
+ *  to logic networks and registers).
+ *
+ */
+
+#ifndef VERILOG_BACKEND_H
+#define VERILOG_BACKEND_H
+
+#include "kernel/rtlil.h"
+#include <stdio.h>
+
+namespace VERILOG_BACKEND {
+	void verilog_backend(FILE *f, std::vector<std::string> args, RTLIL::Design *design);
+}
+
+#endif