yosys/passes/fsm/fsm_detect.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  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
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "kernel/log.h"
#include "kernel/register.h"
#include "kernel/sigtools.h"
#include "kernel/consteval.h"
#include "kernel/celltypes.h"
#include "fsmdata.h"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

static RTLIL::Module *module;
static SigMap assign_map;
typedef std::pair<RTLIL::Cell*, RTLIL::IdString> sig2driver_entry_t;
static SigSet<sig2driver_entry_t> sig2driver, sig2user;
static std::set<RTLIL::Cell*> muxtree_cells;
static SigPool sig_at_port;

static bool check_state_mux_tree(RTLIL::SigSpec old_sig, RTLIL::SigSpec sig, pool<Cell*> &recursion_monitor, dict<RTLIL::SigSpec, bool> &mux_tree_cache)
{
	if (mux_tree_cache.find(sig) != mux_tree_cache.end())
		return mux_tree_cache.at(sig);

	if (sig.is_fully_const() || old_sig == sig) {
ret_true:
		mux_tree_cache[sig] = true;
		return true;
	}

	if (sig_at_port.check_any(assign_map(sig))) {
ret_false:
		mux_tree_cache[sig] = false;
		return false;
	}

	std::set<sig2driver_entry_t> cellport_list;
	sig2driver.find(sig, cellport_list);
	for (auto &cellport : cellport_list)
	{
		if ((cellport.first->type != ID($mux) && cellport.first->type != ID($pmux)) || cellport.second != ID::Y) {
			goto ret_false;
		}

		if (recursion_monitor.count(cellport.first)) {
			log_warning("logic loop in mux tree at signal %s in module %s.\n",
					log_signal(sig), RTLIL::id2cstr(module->name));
			goto ret_false;
		}

		recursion_monitor.insert(cellport.first);

		RTLIL::SigSpec sig_a = assign_map(cellport.first->getPort(ID::A));
		RTLIL::SigSpec sig_b = assign_map(cellport.first->getPort(ID::B));

		if (!check_state_mux_tree(old_sig, sig_a, recursion_monitor, mux_tree_cache)) {
			recursion_monitor.erase(cellport.first);
			goto ret_false;
		}

		for (int i = 0; i < sig_b.size(); i += sig_a.size())
			if (!check_state_mux_tree(old_sig, sig_b.extract(i, sig_a.size()), recursion_monitor, mux_tree_cache)) {
				recursion_monitor.erase(cellport.first);
				goto ret_false;
			}

		recursion_monitor.erase(cellport.first);
		muxtree_cells.insert(cellport.first);
	}

	goto ret_true;
}

static bool check_state_users(RTLIL::SigSpec sig)
{
	if (sig_at_port.check_any(assign_map(sig)))
		return false;

	std::set<sig2driver_entry_t> cellport_list;
	sig2user.find(sig, cellport_list);
	for (auto &cellport : cellport_list) {
		RTLIL::Cell *cell = cellport.first;
		if (muxtree_cells.count(cell) > 0)
			continue;
		if (cell->type == ID($logic_not) && assign_map(cell->getPort(ID::A)) == sig)
			continue;
		if (cellport.second != ID::A && cellport.second != ID::B)
			return false;
		if (!cell->hasPort(ID::A) || !cell->hasPort(ID::B) || !cell->hasPort(ID::Y))
			return false;
		for (auto &port_it : cell->connections())
			if (port_it.first != ID::A && port_it.first != ID::B && port_it.first != ID::Y)
				return false;
		if (assign_map(cell->getPort(ID::A)) == sig && cell->getPort(ID::B).is_fully_const())
			continue;
		if (assign_map(cell->getPort(ID::B)) == sig && cell->getPort(ID::A).is_fully_const())
			continue;
		return false;
	}

	return true;
}

static void detect_fsm(RTLIL::Wire *wire)
{
	bool has_fsm_encoding_attr = wire->attributes.count(ID::fsm_encoding) > 0 && wire->attributes.at(ID::fsm_encoding).decode_string() != "none";
	bool has_fsm_encoding_none = wire->attributes.count(ID::fsm_encoding) > 0 && wire->attributes.at(ID::fsm_encoding).decode_string() == "none";
	bool has_init_attr = wire->attributes.count(ID::init) > 0;
	bool is_module_port = sig_at_port.check_any(assign_map(RTLIL::SigSpec(wire)));
	bool looks_like_state_reg = false, looks_like_good_state_reg = false;
	bool is_self_resetting = false;

	if (has_fsm_encoding_none)
		return;

	if (wire->width <= 1) {
		if (has_fsm_encoding_attr) {
			log_warning("Removing fsm_encoding attribute from 1-bit net: %s.%s\n", log_id(wire->module), log_id(wire));
			wire->attributes.erase(ID::fsm_encoding);
		}
		return;
	}

	std::set<sig2driver_entry_t> cellport_list;
	sig2driver.find(RTLIL::SigSpec(wire), cellport_list);

	for (auto &cellport : cellport_list)
	{
		if ((cellport.first->type != ID($dff) && cellport.first->type != ID($adff)) || cellport.second != ID::Q)
			continue;

		muxtree_cells.clear();
		pool<Cell*> recursion_monitor;
		RTLIL::SigSpec sig_q = assign_map(cellport.first->getPort(ID::Q));
		RTLIL::SigSpec sig_d = assign_map(cellport.first->getPort(ID::D));
		dict<RTLIL::SigSpec, bool> mux_tree_cache;

		if (sig_q != assign_map(wire))
			continue;

		looks_like_state_reg = check_state_mux_tree(sig_q, sig_d, recursion_monitor, mux_tree_cache);
		looks_like_good_state_reg = check_state_users(sig_q);

		if (!looks_like_state_reg)
			break;

		ConstEval ce(wire->module);

		std::set<sig2driver_entry_t> cellport_list;
		sig2user.find(sig_q, cellport_list);

		auto sig_q_bits = sig_q.to_sigbit_pool();

		for (auto &cellport : cellport_list)
		{
			RTLIL::Cell *cell = cellport.first;
			bool set_output = false, clr_output = false;

			if (cell->type.in(ID($ne), ID($reduce_or), ID($reduce_bool)))
				set_output = true;

			if (cell->type.in(ID($eq), ID($logic_not), ID($reduce_and)))
				clr_output = true;

			if (set_output || clr_output) {
				for (auto &port_it : cell->connections())
					if (cell->input(port_it.first))
						for (auto bit : assign_map(port_it.second))
							if (bit.wire != nullptr && !sig_q_bits.count(bit))
								goto next_cellport;
			}

			if (set_output || clr_output) {
				for (auto &port_it : cell->connections())
					if (cell->output(port_it.first)) {
						SigSpec sig = assign_map(port_it.second);
						Const val(set_output ? State::S1 : State::S0, GetSize(sig));
						ce.set(sig, val);
					}
			}
		next_cellport:;
		}

		SigSpec sig_y = sig_d, sig_undef;
		if (ce.eval(sig_y, sig_undef))
			is_self_resetting = true;
	}

	if (has_fsm_encoding_attr)
	{
		vector<string> warnings;

		if (is_module_port)
			warnings.push_back("Forcing FSM recoding on module port might result in larger circuit.\n");

		if (!looks_like_good_state_reg)
			warnings.push_back("Users of state reg look like FSM recoding might result in larger circuit.\n");

		if (has_init_attr)
			warnings.push_back("Initialization value on FSM state register is ignored. Possible simulation-synthesis mismatch!\n");

		if (!looks_like_state_reg)
			warnings.push_back("Doesn't look like a proper FSM. Possible simulation-synthesis mismatch!\n");

		if (is_self_resetting)
			warnings.push_back("FSM seems to be self-resetting. Possible simulation-synthesis mismatch!\n");

		if (!warnings.empty()) {
			string warnmsg = stringf("Regarding the user-specified fsm_encoding attribute on %s.%s:\n", log_id(wire->module), log_id(wire));
			for (auto w : warnings) warnmsg += "    " + w;
			log_warning("%s", warnmsg.c_str());
		} else {
			log("FSM state register %s.%s already has fsm_encoding attribute.\n", log_id(wire->module), log_id(wire));
		}
	}
	else
	if (looks_like_state_reg && looks_like_good_state_reg && !has_init_attr && !is_module_port && !is_self_resetting)
	{
		log("Found FSM state register %s.%s.\n", log_id(wire->module), log_id(wire));
		wire->attributes[ID::fsm_encoding] = RTLIL::Const("auto");
	}
	else
	if (looks_like_state_reg)
	{
		log("Not marking %s.%s as FSM state register:\n", log_id(wire->module), log_id(wire));

		if (is_module_port)
			log("    Register is connected to module port.\n");

		if (!looks_like_good_state_reg)
			log("    Users of register don't seem to benefit from recoding.\n");

		if (has_init_attr)
			log("    Register has an initialization value.\n");

		if (is_self_resetting)
			log("    Circuit seems to be self-resetting.\n");
	}
}

struct FsmDetectPass : public Pass {
	FsmDetectPass() : Pass("fsm_detect", "finding FSMs in design") { }
	void help() override
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    fsm_detect [selection]\n");
		log("\n");
		log("This pass detects finite state machines by identifying the state signal.\n");
		log("The state signal is then marked by setting the attribute 'fsm_encoding'\n");
		log("on the state signal to \"auto\".\n");
		log("\n");
		log("Existing 'fsm_encoding' attributes are not changed by this pass.\n");
		log("\n");
		log("Signals can be protected from being detected by this pass by setting the\n");
		log("'fsm_encoding' attribute to \"none\".\n");
		log("\n");
	}
	void execute(std::vector<std::string> args, RTLIL::Design *design) override
	{
		log_header(design, "Executing FSM_DETECT pass (finding FSMs in design).\n");
		extra_args(args, 1, design);

		CellTypes ct;
		ct.setup_internals();
		ct.setup_internals_anyinit();
		ct.setup_internals_mem();
		ct.setup_stdcells();
		ct.setup_stdcells_mem();

		for (auto mod : design->selected_modules())
		{
			module = mod;
			assign_map.set(module);

			sig2driver.clear();
			sig2user.clear();
			sig_at_port.clear();
			for (auto cell : module->cells())
				for (auto &conn_it : cell->connections()) {
					if (ct.cell_output(cell->type, conn_it.first) || !ct.cell_known(cell->type)) {
						RTLIL::SigSpec sig = conn_it.second;
						assign_map.apply(sig);
						sig2driver.insert(sig, sig2driver_entry_t(cell, conn_it.first));
					}
					if (!ct.cell_known(cell->type) || ct.cell_input(cell->type, conn_it.first)) {
						RTLIL::SigSpec sig = conn_it.second;
						assign_map.apply(sig);
						sig2user.insert(sig, sig2driver_entry_t(cell, conn_it.first));
					}
				}

			for (auto wire : module->wires())
				if (wire->port_id != 0)
					sig_at_port.add(assign_map(wire));

			for (auto wire : module->selected_wires())
				detect_fsm(wire);
		}

		assign_map.clear();
		sig2driver.clear();
		sig2user.clear();
		muxtree_cells.clear();
	}
} FsmDetectPass;

PRIVATE_NAMESPACE_END