1 files changed, 552 insertions, 126 deletions

diff --git a/passes/sat/sim.cc b/passes/sat/sim.cc
index fb496ff87..a7c109374 100644
--- a/passes/sat/sim.cc
+++ b/passes/sat/sim.cc
@@ -1,7 +1,7 @@
 /*
  *  yosys -- Yosys Open SYnthesis Suite
  *
- *  Copyright (C) 2012  Clifford Wolf <clifford@clifford.at>
+ *  Copyright (C) 2012  Claire Xenia Wolf <claire@yosyshq.com>
  *
  *  Permission to use, copy, modify, and/or distribute this software for any
  *  purpose with or without fee is hereby granted, provided that the above
@@ -20,10 +20,50 @@
 #include "kernel/yosys.h"
 #include "kernel/sigtools.h"
 #include "kernel/celltypes.h"
+#include "kernel/mem.h"
+#include "kernel/fstdata.h"
+
+#include <ctime>
 
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
+enum class SimulationMode {
+	sim,
+	cmp,
+	gold,
+	gate,
+};
+
+static const std::map<std::string, int> g_units =
+{
+	{ "",    -9 }, // default is ns
+	{ "s",    0 },
+	{ "ms",  -3 },
+	{ "us",  -6 },
+	{ "ns",  -9 },
+	{ "ps", -12 },
+	{ "fs", -15 },
+	{ "as", -18 },
+	{ "zs", -21 },
+};
+
+static double stringToTime(std::string str)
+{
+	if (str=="END") return -1;
+
+	char *endptr;
+	long value = strtol(str.c_str(), &endptr, 10);
+
+	if (g_units.find(endptr)==g_units.end())
+		log_error("Cannot parse '%s', bad unit '%s'\n", str.c_str(), endptr);
+
+	if (value < 0)
+		log_error("Time value '%s' must be positive\n", str.c_str());
+
+	return value * pow(10.0, g_units.at(endptr));
+}
+
 struct SimShared
 {
 	bool debug = false;
@@ -31,6 +71,11 @@ struct SimShared
 	bool writeback = false;
 	bool zinit = false;
 	int rstlen = 1;
+	FstData *fst = nullptr;
+	double start_time = 0;
+	double stop_time = -1;
+	SimulationMode sim_mode = SimulationMode::sim;
+	bool cycles_set = false;
 };
 
 void zinit(State &v)
@@ -48,7 +93,8 @@ void zinit(Const &v)
 struct SimInstance
 {
 	SimShared *shared;
-
+	
+	std::string scope;
 	Module *module;
 	Cell *instance;
 
@@ -62,6 +108,7 @@ struct SimInstance
 
 	pool<SigBit> dirty_bits;
 	pool<Cell*> dirty_cells;
+	pool<IdString> dirty_memories;
 	pool<SimInstance*, hash_ptr_ops> dirty_children;
 
 	struct ff_state_t
@@ -72,21 +119,27 @@ struct SimInstance
 
 	struct mem_state_t
 	{
-		Const past_wr_clk;
-		Const past_wr_en;
-		Const past_wr_addr;
-		Const past_wr_data;
+		Mem *mem;
+		std::vector<Const> past_wr_clk;
+		std::vector<Const> past_wr_en;
+		std::vector<Const> past_wr_addr;
+		std::vector<Const> past_wr_data;
 		Const data;
 	};
 
 	dict<Cell*, ff_state_t> ff_database;
-	dict<Cell*, mem_state_t> mem_database;
+	dict<IdString, mem_state_t> mem_database;
 	pool<Cell*> formal_database;
+	dict<Cell*, IdString> mem_cells;
+
+	std::vector<Mem> memories;
 
 	dict<Wire*, pair<int, Const>> vcd_database;
+	dict<Wire*, pair<fstHandle, Const>> fst_database;
+	dict<Wire*, fstHandle> fst_handles;
 
-	SimInstance(SimShared *shared, Module *module, Cell *instance = nullptr, SimInstance *parent = nullptr) :
-			shared(shared), module(module), instance(instance), parent(parent), sigmap(module)
+	SimInstance(SimShared *shared, std::string scope, Module *module, Cell *instance = nullptr, SimInstance *parent = nullptr) :
+			shared(shared), scope(scope), module(module), instance(instance), parent(parent), sigmap(module)
 	{
 		log_assert(module);
 
@@ -108,6 +161,13 @@ struct SimInstance
 				}
 			}
 
+			if ((shared->fst) && !(shared->hide_internal && wire->name[0] == '$')) {
+				fstHandle id = shared->fst->getHandle(scope + "." + RTLIL::unescape_id(wire->name));
+				if (id==0 && wire->name.isPublic())
+					log_warning("Unable to found wire %s in input file.\n", (scope + "." + RTLIL::unescape_id(wire->name)).c_str());
+				fst_handles[wire] = id;
+			}
+
 			if (wire->attributes.count(ID::init)) {
 				Const initval = wire->attributes.at(ID::init);
 				for (int i = 0; i < GetSize(sig) && i < GetSize(initval); i++)
@@ -118,12 +178,25 @@ struct SimInstance
 			}
 		}
 
+		memories = Mem::get_all_memories(module);
+		for (auto &mem : memories) {
+			auto &mdb = mem_database[mem.memid];
+			mdb.mem = &mem;
+			for (auto &port : mem.wr_ports) {
+				mdb.past_wr_clk.push_back(Const(State::Sx));
+				mdb.past_wr_en.push_back(Const(State::Sx, GetSize(port.en)));
+				mdb.past_wr_addr.push_back(Const(State::Sx, GetSize(port.addr)));
+				mdb.past_wr_data.push_back(Const(State::Sx, GetSize(port.data)));
+			}
+			mdb.data = mem.get_init_data();
+		}
+
 		for (auto cell : module->cells())
 		{
 			Module *mod = module->design->module(cell->type);
 
 			if (mod != nullptr) {
-				dirty_children.insert(new SimInstance(shared, mod, cell, this));
+				dirty_children.insert(new SimInstance(shared, scope + "." + RTLIL::unescape_id(cell->name), mod, cell, this));
 			}
 
 			for (auto &port : cell->connections()) {
@@ -143,29 +216,9 @@ struct SimInstance
 				ff_database[cell] = ff;
 			}
 
-			if (cell->type == ID($mem))
+			if (cell->is_mem_cell())
 			{
-				mem_state_t mem;
-
-				mem.past_wr_clk = Const(State::Sx, GetSize(cell->getPort(ID::WR_CLK)));
-				mem.past_wr_en = Const(State::Sx, GetSize(cell->getPort(ID::WR_EN)));
-				mem.past_wr_addr = Const(State::Sx, GetSize(cell->getPort(ID::WR_ADDR)));
-				mem.past_wr_data = Const(State::Sx, GetSize(cell->getPort(ID::WR_DATA)));
-
-				mem.data = cell->getParam(ID::INIT);
-				int sz = cell->getParam(ID::SIZE).as_int() * cell->getParam(ID::WIDTH).as_int();
-
-				if (GetSize(mem.data) > sz)
-					mem.data.bits.resize(sz);
-
-				while (GetSize(mem.data) < sz)
-					mem.data.bits.push_back(State::Sx);
-
-				mem_database[cell] = mem;
-			}
-			if (cell->type.in(ID($memwr),ID($memrd)))
-			{
-				log_error("$memrd and $memwr cells have to be merged to stand-alone $mem cells (execute memory_collect pass)\n");
+				mem_cells[cell] = cell->parameters.at(ID::MEMID).decode_string();
 			}
 			if (cell->type.in(ID($assert), ID($cover), ID($assume))) {
 				formal_database.insert(cell);
@@ -188,7 +241,8 @@ struct SimInstance
 
 			for (auto &it : mem_database) {
 				mem_state_t &mem = it.second;
-				zinit(mem.past_wr_en);
+				for (auto &val : mem.past_wr_en)
+					zinit(val);
 				zinit(mem.data);
 			}
 		}
@@ -259,37 +313,9 @@ struct SimInstance
 		if (formal_database.count(cell))
 			return;
 
-		if (mem_database.count(cell))
+		if (mem_cells.count(cell))
 		{
-			mem_state_t &mem = mem_database.at(cell);
-
-			int num_rd_ports = cell->getParam(ID::RD_PORTS).as_int();
-
-			int size = cell->getParam(ID::SIZE).as_int();
-			int offset = cell->getParam(ID::OFFSET).as_int();
-			int abits = cell->getParam(ID::ABITS).as_int();
-			int width = cell->getParam(ID::WIDTH).as_int();
-
-			if (cell->getParam(ID::RD_CLK_ENABLE).as_bool())
-				log_error("Memory %s.%s has clocked read ports. Run 'memory' with -nordff.\n", log_id(module), log_id(cell));
-
-			SigSpec rd_addr_sig = cell->getPort(ID::RD_ADDR);
-			SigSpec rd_data_sig = cell->getPort(ID::RD_DATA);
-
-			for (int port_idx = 0; port_idx < num_rd_ports; port_idx++)
-			{
-				Const addr = get_state(rd_addr_sig.extract(port_idx*abits, abits));
-				Const data = Const(State::Sx, width);
-
-				if (addr.is_fully_def()) {
-					int index = addr.as_int() - offset;
-					if (index >= 0 && index < size)
-						data = mem.data.extract(index*width, width);
-				}
-
-				set_state(rd_data_sig.extract(port_idx*width, width), data);
-			}
-
+			dirty_memories.insert(mem_cells[cell]);
 			return;
 		}
 
@@ -297,7 +323,7 @@ struct SimInstance
 		{
 			auto child = children.at(cell);
 			for (auto &conn: cell->connections())
-				if (cell->input(conn.first)) {
+				if (cell->input(conn.first) && GetSize(conn.second)) {
 					Const value = get_state(conn.second);
 					child->set_state(child->module->wire(conn.first), value);
 				}
@@ -339,6 +365,12 @@ struct SimInstance
 				return;
 			}
 
+			// (A,S -> Y) cells
+			if (has_a && !has_b && !has_c && !has_d && has_s && has_y) {
+				set_state(sig_y, CellTypes::eval(cell, get_state(sig_a), get_state(sig_s)));
+				return;
+			}
+
 			// (A,B,S -> Y) cells
 			if (has_a && has_b && !has_c && !has_d && has_s && has_y) {
 				set_state(sig_y, CellTypes::eval(cell, get_state(sig_a), get_state(sig_b), get_state(sig_s)));
@@ -352,6 +384,29 @@ struct SimInstance
 		log_error("Unsupported cell type: %s (%s.%s)\n", log_id(cell->type), log_id(module), log_id(cell));
 	}
 
+	void update_memory(IdString id) {
+		auto &mdb = mem_database[id];
+		auto &mem = *mdb.mem;
+
+		for (int port_idx = 0; port_idx < GetSize(mem.rd_ports); port_idx++)
+		{
+			auto &port = mem.rd_ports[port_idx];
+			Const addr = get_state(port.addr);
+			Const data = Const(State::Sx, mem.width << port.wide_log2);
+
+			if (port.clk_enable)
+				log_error("Memory %s.%s has clocked read ports. Run 'memory' with -nordff.\n", log_id(module), log_id(mem.memid));
+
+			if (addr.is_fully_def()) {
+				int index = addr.as_int() - mem.start_offset;
+				if (index >= 0 && index < mem.size)
+					data = mdb.data.extract(index*mem.width, mem.width << port.wide_log2);
+			}
+
+			set_state(port.data, data);
+		}
+	}
+
 	void update_ph1()
 	{
 		pool<Cell*> queue_cells;
@@ -383,6 +438,10 @@ struct SimInstance
 				continue;
 			}
 
+			for (auto &memid : dirty_memories)
+				update_memory(memid);
+			dirty_memories.clear();
+
 			for (auto wire : queue_outports)
 				if (instance->hasPort(wire->name)) {
 					Const value = get_state(wire);
@@ -426,50 +485,40 @@ struct SimInstance
 
 		for (auto &it : mem_database)
 		{
-			Cell *cell = it.first;
-			mem_state_t &mem = it.second;
-
-			int num_wr_ports = cell->getParam(ID::WR_PORTS).as_int();
-
-			int size = cell->getParam(ID::SIZE).as_int();
-			int offset = cell->getParam(ID::OFFSET).as_int();
-			int abits = cell->getParam(ID::ABITS).as_int();
-			int width = cell->getParam(ID::WIDTH).as_int();
+			mem_state_t &mdb = it.second;
+			auto &mem = *mdb.mem;
 
-			Const wr_clk_enable = cell->getParam(ID::WR_CLK_ENABLE);
-			Const wr_clk_polarity = cell->getParam(ID::WR_CLK_POLARITY);
-			Const current_wr_clk  = get_state(cell->getPort(ID::WR_CLK));
-
-			for (int port_idx = 0; port_idx < num_wr_ports; port_idx++)
+			for (int port_idx = 0; port_idx < GetSize(mem.wr_ports); port_idx++)
 			{
+				auto &port = mem.wr_ports[port_idx];
 				Const addr, data, enable;
 
-				if (wr_clk_enable[port_idx] == State::S0)
+				if (!port.clk_enable)
 				{
-					addr = get_state(cell->getPort(ID::WR_ADDR).extract(port_idx*abits, abits));
-					data = get_state(cell->getPort(ID::WR_DATA).extract(port_idx*width, width));
-					enable = get_state(cell->getPort(ID::WR_EN).extract(port_idx*width, width));
+					addr = get_state(port.addr);
+					data = get_state(port.data);
+					enable = get_state(port.en);
 				}
 				else
 				{
-					if (wr_clk_polarity[port_idx] == State::S1 ?
-							(mem.past_wr_clk[port_idx] == State::S1 || current_wr_clk[port_idx] != State::S1) :
-							(mem.past_wr_clk[port_idx] == State::S0 || current_wr_clk[port_idx] != State::S0))
+					if (port.clk_polarity ?
+							(mdb.past_wr_clk[port_idx] == State::S1 || get_state(port.clk) != State::S1) :
+							(mdb.past_wr_clk[port_idx] == State::S0 || get_state(port.clk) != State::S0))
 						continue;
 
-					addr = mem.past_wr_addr.extract(port_idx*abits, abits);
-					data = mem.past_wr_data.extract(port_idx*width, width);
-					enable = mem.past_wr_en.extract(port_idx*width, width);
+					addr = mdb.past_wr_addr[port_idx];
+					data = mdb.past_wr_data[port_idx];
+					enable = mdb.past_wr_en[port_idx];
 				}
 
 				if (addr.is_fully_def())
 				{
-					int index = addr.as_int() - offset;
-					if (index >= 0 && index < size)
-						for (int i = 0; i < width; i++)
-							if (enable[i] == State::S1 && mem.data.bits.at(index*width+i) != data[i]) {
-								mem.data.bits.at(index*width+i) = data[i];
-								dirty_cells.insert(cell);
+					int index = addr.as_int() - mem.start_offset;
+					if (index >= 0 && index < mem.size)
+						for (int i = 0; i < (mem.width << port.wide_log2); i++)
+							if (enable[i] == State::S1 && mdb.data.bits.at(index*mem.width+i) != data[i]) {
+								mdb.data.bits.at(index*mem.width+i) = data[i];
+								dirty_memories.insert(mem.memid);
 								did_something = true;
 							}
 				}
@@ -500,13 +549,15 @@ struct SimInstance
 
 		for (auto &it : mem_database)
 		{
-			Cell *cell = it.first;
 			mem_state_t &mem = it.second;
 
-			mem.past_wr_clk  = get_state(cell->getPort(ID::WR_CLK));
-			mem.past_wr_en   = get_state(cell->getPort(ID::WR_EN));
-			mem.past_wr_addr = get_state(cell->getPort(ID::WR_ADDR));
-			mem.past_wr_data = get_state(cell->getPort(ID::WR_DATA));
+			for (int i = 0; i < GetSize(mem.mem->wr_ports); i++) {
+				auto &port = mem.mem->wr_ports[i];
+				mem.past_wr_clk[i]  = get_state(port.clk);
+				mem.past_wr_en[i]   = get_state(port.en);
+				mem.past_wr_addr[i] = get_state(port.addr);
+				mem.past_wr_data[i] = get_state(port.data);
+			}
 		}
 
 		for (auto cell : formal_database)
@@ -561,17 +612,14 @@ struct SimInstance
 
 		for (auto &it : mem_database)
 		{
-			Cell *cell = it.first;
 			mem_state_t &mem = it.second;
-			Const initval = mem.data;
-
-			while (GetSize(initval) >= 2) {
-				if (initval[GetSize(initval)-1] != State::Sx) break;
-				if (initval[GetSize(initval)-2] != State::Sx) break;
-				initval.bits.pop_back();
-			}
-
-			cell->setParam(ID::INIT, initval);
+			mem.mem->clear_inits();
+			MemInit minit;
+			minit.addr = mem.mem->start_offset;
+			minit.data = mem.data;
+			minit.en = Const(State::S1, mem.mem->width);
+			mem.mem->inits.push_back(minit);
+			mem.mem->emit();
 		}
 
 		for (auto it : children)
@@ -626,13 +674,125 @@ struct SimInstance
 		for (auto child : children)
 			child.second->write_vcd_step(f);
 	}
+
+	void write_fst_header(struct fstContext *f)
+	{
+		fstWriterSetScope(f, FST_ST_VCD_MODULE, stringf("%s",log_id(name())).c_str(), nullptr);
+		for (auto wire : module->wires())
+		{
+			if (shared->hide_internal && wire->name[0] == '$')
+				continue;
+
+			fstHandle id = fstWriterCreateVar(f, FST_VT_VCD_WIRE, FST_VD_IMPLICIT, GetSize(wire),
+												stringf("%s%s", wire->name[0] == '$' ? "\\" : "", log_id(wire)).c_str(), 0);
+			fst_database[wire] = make_pair(id, Const());
+		}
+
+		for (auto child : children)
+			child.second->write_fst_header(f);
+
+		fstWriterSetUpscope(f);
+	}
+
+	void write_fst_step(struct fstContext *f)
+	{
+		for (auto &it : fst_database)
+		{
+			Wire *wire = it.first;
+			Const value = get_state(wire);
+			fstHandle id = it.second.first;
+
+			if (it.second.second == value)
+				continue;
+
+			it.second.second = value;
+			std::stringstream ss;
+			for (int i = GetSize(value)-1; i >= 0; i--) {
+				switch (value[i]) {
+					case State::S0: ss << "0"; break;
+					case State::S1: ss << "1"; break;
+					case State::Sx: ss << "x"; break;
+					default: ss << "z";
+				}
+			}
+			fstWriterEmitValueChange(f, id, ss.str().c_str());
+		}
+
+		for (auto child : children)
+			child.second->write_fst_step(f);
+	}
+
+	void setInitState(uint64_t time)
+	{
+		for (auto &it : ff_database)
+		{
+			Cell *cell = it.first;
+			
+			SigSpec qsig = cell->getPort(ID::Q);
+			if (qsig.is_wire()) {
+				IdString name = qsig.as_wire()->name;
+				fstHandle id = shared->fst->getHandle(scope + "." + RTLIL::unescape_id(name));
+				if (id==0 && name.isPublic())
+					log_warning("Unable to found wire %s in input file.\n", (scope + "." + RTLIL::unescape_id(name)).c_str());
+				if (id!=0) {
+					Const fst_val = Const::from_string(shared->fst->valueAt(id, time));
+					set_state(qsig, fst_val);
+				}
+			}
+		}
+		for (auto child : children)
+			child.second->setInitState(time);
+	}
+
+	bool checkSignals(uint64_t time)
+	{
+		bool retVal = false;
+		for(auto &item : fst_handles) {
+			if (item.second==0) continue; // Ignore signals not found
+			Const fst_val = Const::from_string(shared->fst->valueAt(item.second, time));
+			Const sim_val = get_state(item.first);
+			if (sim_val.size()!=fst_val.size())
+				log_error("Signal '%s' size is different in gold and gate.\n", log_id(item.first));
+			if (shared->sim_mode == SimulationMode::sim) {
+				// No checks performed when using stimulus
+			} else if (shared->sim_mode == SimulationMode::gate && !fst_val.is_fully_def()) { // FST data contains X
+				for(int i=0;i<fst_val.size();i++) {
+					if (fst_val[i]!=State::Sx && fst_val[i]!=sim_val[i]) {
+						log_warning("Signal '%s' in file %s in simulation %s\n", log_id(item.first), log_signal(fst_val), log_signal(sim_val));
+						retVal = true;
+						break;
+					}
+				}
+			} else if (shared->sim_mode == SimulationMode::gold && !sim_val.is_fully_def()) { // sim data contains X
+				for(int i=0;i<sim_val.size();i++) {
+					if (sim_val[i]!=State::Sx && fst_val[i]!=sim_val[i]) {
+						log_warning("Signal '%s' in file %s in simulation %s\n", log_id(item.first), log_signal(fst_val), log_signal(sim_val));
+						retVal = true;
+						break;
+					}
+				}
+			} else {
+				if (fst_val!=sim_val) {
+					log_warning("Signal '%s' in file %s in simulation '%s'\n", log_id(item.first), log_signal(fst_val), log_signal(sim_val));
+					retVal = true;
+				}
+			}
+		}
+		for (auto child : children)
+			retVal |= child.second->checkSignals(time);
+		return retVal;
+	}
 };
 
 struct SimWorker : SimShared
 {
 	SimInstance *top = nullptr;
 	std::ofstream vcdfile;
+	struct fstContext *fstfile = nullptr;
 	pool<IdString> clock, clockn, reset, resetn;
+	std::string timescale;
+	std::string sim_filename;
+	std::string scope;
 
 	~SimWorker()
 	{
@@ -641,8 +801,16 @@ struct SimWorker : SimShared
 
 	void write_vcd_header()
 	{
-		if (!vcdfile.is_open())
-			return;
+		vcdfile << stringf("$version %s $end\n", yosys_version_str);
+
+		std::time_t t = std::time(nullptr);
+		char mbstr[255];
+		if (std::strftime(mbstr, sizeof(mbstr), "%c", std::localtime(&t))) {
+			vcdfile << stringf("$date ") << mbstr << stringf(" $end\n");
+		}
+
+		if (!timescale.empty())
+			vcdfile << stringf("$timescale %s $end\n", timescale.c_str());
 
 		int id = 1;
 		top->write_vcd_header(vcdfile, id);
@@ -652,13 +820,53 @@ struct SimWorker : SimShared
 
 	void write_vcd_step(int t)
 	{
-		if (!vcdfile.is_open())
-			return;
-
 		vcdfile << stringf("#%d\n", t);
 		top->write_vcd_step(vcdfile);
 	}
 
+	void write_fst_header()
+	{
+		std::time_t t = std::time(nullptr);
+		fstWriterSetDate(fstfile, asctime(std::localtime(&t)));
+		fstWriterSetVersion(fstfile, yosys_version_str);
+		if (!timescale.empty())
+			fstWriterSetTimescaleFromString(fstfile, timescale.c_str());
+
+		fstWriterSetPackType(fstfile, FST_WR_PT_FASTLZ);
+		fstWriterSetRepackOnClose(fstfile, 1);
+	   
+		top->write_fst_header(fstfile);
+	}
+
+	void write_fst_step(int t)
+	{
+		fstWriterEmitTimeChange(fstfile, t);
+
+		top->write_fst_step(fstfile);
+	}
+
+	void write_output_header()
+	{
+		if (vcdfile.is_open())
+			write_vcd_header();
+		if (fstfile)
+			write_fst_header();
+	}
+
+	void write_output_step(int t)
+	{
+		if (vcdfile.is_open())
+			write_vcd_step(t);
+		if (fstfile)
+			write_fst_step(t);
+	}
+
+	void write_output_end()
+	{
+		if (fstfile)
+			fstWriterClose(fstfile);
+	}
+
 	void update()
 	{
 		while (1)
@@ -697,7 +905,7 @@ struct SimWorker : SimShared
 	void run(Module *topmod, int numcycles)
 	{
 		log_assert(top == nullptr);
-		top = new SimInstance(this, topmod);
+		top = new SimInstance(this, scope, topmod);
 
 		if (debug)
 			log("\n===== 0 =====\n");
@@ -712,24 +920,25 @@ struct SimWorker : SimShared
 
 		update();
 
-		write_vcd_header();
-		write_vcd_step(0);
+		write_output_header();
+		write_output_step(0);
 
 		for (int cycle = 0; cycle < numcycles; cycle++)
 		{
 			if (debug)
 				log("\n===== %d =====\n", 10*cycle + 5);
-
+			else
+				log("Simulating cycle %d.\n", (cycle*2)+1);
 			set_inports(clock, State::S0);
 			set_inports(clockn, State::S1);
 
 			update();
-			write_vcd_step(10*cycle + 5);
+			write_output_step(10*cycle + 5);
 
 			if (debug)
 				log("\n===== %d =====\n", 10*cycle + 10);
 			else
-				log("Simulating cycle %d.\n", cycle+1);
+				log("Simulating cycle %d.\n", (cycle*2)+2);
 
 			set_inports(clock, State::S1);
 			set_inports(clockn, State::S0);
@@ -740,16 +949,137 @@ struct SimWorker : SimShared
 			}
 
 			update();
-			write_vcd_step(10*cycle + 10);
+			write_output_step(10*cycle + 10);
 		}
 
-		write_vcd_step(10*numcycles + 2);
+		write_output_step(10*numcycles + 2);
+
+		write_output_end();
 
 		if (writeback) {
 			pool<Module*> wbmods;
 			top->writeback(wbmods);
 		}
 	}
+
+	void run_cosim(Module *topmod, int numcycles)
+	{
+		log_assert(top == nullptr);
+		fst = new FstData(sim_filename);
+
+		if (scope.empty())
+			log_error("Scope must be defined for co-simulation.\n");
+
+		top = new SimInstance(this, scope, topmod);
+
+		std::vector<fstHandle> fst_clock;
+
+		for (auto portname : clock)
+		{
+			Wire *w = topmod->wire(portname);
+			if (!w)
+				log_error("Can't find port %s on module %s.\n", log_id(portname), log_id(top->module));
+			if (!w->port_input)
+				log_error("Clock port %s on module %s is not input.\n", log_id(portname), log_id(top->module));
+			fstHandle id = fst->getHandle(scope + "." + RTLIL::unescape_id(portname));
+			if (id==0)
+				log_error("Can't find port %s.%s in FST.\n", scope.c_str(), log_id(portname));
+			fst_clock.push_back(id);
+		}
+		for (auto portname : clockn)
+		{
+			Wire *w = topmod->wire(portname);
+			if (!w)
+				log_error("Can't find port %s on module %s.\n", log_id(portname), log_id(top->module));
+			if (!w->port_input)
+				log_error("Clock port %s on module %s is not input.\n", log_id(portname), log_id(top->module));
+			fstHandle id = fst->getHandle(scope + "." + RTLIL::unescape_id(portname));
+			if (id==0)
+				log_error("Can't find port %s.%s in FST.\n", scope.c_str(), log_id(portname));
+			fst_clock.push_back(id);
+		}
+		if (fst_clock.size()==0)
+			log_error("No clock signals defined for input file\n");
+
+		SigMap sigmap(topmod);
+		std::map<Wire*,fstHandle> inputs;
+
+		for (auto wire : topmod->wires()) {
+			if (wire->port_input) {
+				fstHandle id = fst->getHandle(scope + "." + RTLIL::unescape_id(wire->name));
+				if (id==0)
+					log_error("Unable to find required '%s' signal in file\n",(scope + "." + RTLIL::unescape_id(wire->name)).c_str());
+				inputs[wire] = id;
+			}
+		}
+
+		uint64_t startCount = 0;
+		uint64_t stopCount = 0;
+		if (start_time==0) {
+			if (start_time < fst->getStartTime())
+				log_warning("Start time is before simulation file start time\n");
+			startCount = fst->getStartTime();
+		} else if (start_time==-1) 
+			startCount = fst->getEndTime();
+		else {
+			startCount = start_time / fst->getTimescale();
+			if (startCount > fst->getEndTime()) {
+				startCount = fst->getEndTime();
+				log_warning("Start time is after simulation file end time\n");
+			}
+		}
+		if (stop_time==0) {
+			if (stop_time < fst->getStartTime())
+				log_warning("Stop time is before simulation file start time\n");
+			stopCount = fst->getStartTime();
+		} else if (stop_time==-1) 
+			stopCount = fst->getEndTime();
+		else {
+			stopCount = stop_time / fst->getTimescale();
+			if (stopCount > fst->getEndTime()) {
+				stopCount = fst->getEndTime();
+				log_warning("Stop time is after simulation file end time\n");
+			}
+		}
+		if (stopCount<startCount) {
+			log_error("Stop time is before start time\n");
+		}
+		auto samples = fst->getAllEdges(fst_clock, startCount, stopCount);
+
+		// Limit to number of cycles if provided
+		if (cycles_set && ((size_t)(numcycles *2) < samples.size()))
+			samples.erase(samples.begin() + (numcycles*2), samples.end());
+
+		// Add setup time (start time)
+		if (samples.empty() || samples.front()!=startCount)
+			samples.insert(samples.begin(), startCount);
+
+		fst->reconstructAllAtTimes(samples);
+		bool initial = true;
+		int cycle = 0;
+		log("Co-simulation from %lu%s to %lu%s\n", (unsigned long)startCount, fst->getTimescaleString(), (unsigned long)stopCount, fst->getTimescaleString());
+		for(auto &time : samples) {
+			log("Co-simulating cycle %d [%lu%s].\n", cycle, (unsigned long)time, fst->getTimescaleString());
+			for(auto &item : inputs) {
+				std::string v = fst->valueAt(item.second, time);
+				top->set_state(item.first, Const::from_string(v));
+			}
+			if (initial) {
+				top->setInitState(time);
+				initial = false;
+			}
+			update();
+
+			bool status = top->checkSignals(time);
+			if (status)
+				log_error("Signal difference\n");
+			cycle++;
+		}
+		if (writeback) {
+			pool<Module*> wbmods;
+			top->writeback(wbmods);
+		}
+	}
 };
 
 struct SimPass : public Pass {
@@ -765,6 +1095,9 @@ struct SimPass : public Pass {
 		log("    -vcd <filename>\n");
 		log("        write the simulation results to the given VCD file\n");
 		log("\n");
+		log("    -fst <filename>\n");
+		log("        write the simulation results to the given FST file\n");
+		log("\n");
 		log("    -clock <portname>\n");
 		log("        name of top-level clock input\n");
 		log("\n");
@@ -783,15 +1116,45 @@ struct SimPass : public Pass {
 		log("    -zinit\n");
 		log("        zero-initialize all uninitialized regs and memories\n");
 		log("\n");
+		log("    -timescale <string>\n");
+		log("        include the specified timescale declaration in the vcd\n");
+		log("\n");
 		log("    -n <integer>\n");
-		log("        number of cycles to simulate (default: 20)\n");
+		log("        number of clock cycles to simulate (default: 20)\n");
 		log("\n");
 		log("    -a\n");
-		log("        include all nets in VCD output, not just those with public names\n");
+		log("        use all nets in VCD/FST operations, not just those with public names\n");
 		log("\n");
 		log("    -w\n");
 		log("        writeback mode: use final simulation state as new init state\n");
 		log("\n");
+		log("    -r\n");
+		log("        read simulation results file (file formats supported: FST)\n");
+		log("\n");
+		log("    -scope\n");
+		log("        scope of simulation top model\n");
+		log("\n");
+		log("    -at <time>\n");
+		log("        sets start and stop time\n");
+		log("\n");
+		log("    -start <time>\n");
+		log("        start co-simulation in arbitary time (default 0)\n");
+		log("\n");
+		log("    -stop <time>\n");
+		log("        stop co-simulation in arbitary time (default END)\n");
+		log("\n");
+		log("    -sim\n");
+		log("        simulation with stimulus from FST (default)\n");
+		log("\n");
+		log("    -sim-cmp\n");
+		log("        co-simulation expect exact match\n");
+		log("\n");
+		log("    -sim-gold\n");
+		log("        co-simulation, x in simulation can match any value in FST\n");
+		log("\n");
+		log("    -sim-gate\n");
+		log("        co-simulation, x in FST can match any value in simulation\n");
+		log("\n");
 		log("    -d\n");
 		log("        enable debug output\n");
 		log("\n");
@@ -800,17 +1163,27 @@ struct SimPass : public Pass {
 	{
 		SimWorker worker;
 		int numcycles = 20;
+		bool start_set = false, stop_set = false, at_set = false;
 
 		log_header(design, "Executing SIM pass (simulate the circuit).\n");
 
 		size_t argidx;
 		for (argidx = 1; argidx < args.size(); argidx++) {
 			if (args[argidx] == "-vcd" && argidx+1 < args.size()) {
-				worker.vcdfile.open(args[++argidx].c_str());
+				std::string vcd_filename = args[++argidx];
+				rewrite_filename(vcd_filename);
+				worker.vcdfile.open(vcd_filename.c_str());
+				continue;
+			}
+			if (args[argidx] == "-fst" && argidx+1 < args.size()) {
+				std::string fst_filename = args[++argidx];
+				rewrite_filename(fst_filename);
+				worker.fstfile = (struct fstContext *)fstWriterCreate(fst_filename.c_str(),1);
 				continue;
 			}
 			if (args[argidx] == "-n" && argidx+1 < args.size()) {
 				numcycles = atoi(args[++argidx].c_str());
+				worker.cycles_set = true;
 				continue;
 			}
 			if (args[argidx] == "-rstlen" && argidx+1 < args.size()) {
@@ -833,6 +1206,10 @@ struct SimPass : public Pass {
 				worker.resetn.insert(RTLIL::escape_id(args[++argidx]));
 				continue;
 			}
+			if (args[argidx] == "-timescale" && argidx+1 < args.size()) {
+				worker.timescale = args[++argidx];
+				continue;
+			}
 			if (args[argidx] == "-a") {
 				worker.hide_internal = false;
 				continue;
@@ -849,9 +1226,55 @@ struct SimPass : public Pass {
 				worker.zinit = true;
 				continue;
 			}
+			if (args[argidx] == "-r" && argidx+1 < args.size()) {
+				std::string sim_filename = args[++argidx];
+				rewrite_filename(sim_filename);
+				worker.sim_filename = sim_filename;
+				continue;
+			}
+			if (args[argidx] == "-scope" && argidx+1 < args.size()) {
+				worker.scope = args[++argidx];
+				continue;
+			}
+			if (args[argidx] == "-start" && argidx+1 < args.size()) {
+				worker.start_time = stringToTime(args[++argidx]);
+				start_set = true;
+				continue;
+			}
+			if (args[argidx] == "-stop" && argidx+1 < args.size()) {
+				worker.stop_time = stringToTime(args[++argidx]);
+				stop_set = true;
+				continue;
+			}
+			if (args[argidx] == "-at" && argidx+1 < args.size()) {
+				worker.start_time = stringToTime(args[++argidx]);
+				worker.stop_time = worker.start_time;
+				at_set = true;
+				continue;
+			}
+			if (args[argidx] == "-sim") {
+				worker.sim_mode = SimulationMode::sim;
+				continue;
+			}
+			if (args[argidx] == "-sim-cmp") {
+				worker.sim_mode = SimulationMode::cmp;
+				continue;
+			}
+			if (args[argidx] == "-sim-gold") {
+				worker.sim_mode = SimulationMode::gold;
+				continue;
+			}
+			if (args[argidx] == "-sim-gate") {
+				worker.sim_mode = SimulationMode::gate;
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
+		if (at_set && (start_set || stop_set || worker.cycles_set))
+			log_error("'at' option can only be defined separate of 'start','stop' and 'n'\n");
+		if (stop_set && worker.cycles_set)
+			log_error("'stop' and 'n' can only be used exclusively'\n");
 
 		Module *top_mod = nullptr;
 
@@ -867,7 +1290,10 @@ struct SimPass : public Pass {
 			top_mod = mods.front();
 		}
 
-		worker.run(top_mod, numcycles);
+		if (worker.sim_filename.empty())
+			worker.run(top_mod, numcycles);
+		else
+			worker.run_cosim(top_mod, numcycles);
 	}
 } SimPass;