yosys/passes/proc/proc_dff.cc

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2012  Claire Xenia Wolf <[email protected]>
 *
 *  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/register.h"
#include "kernel/sigtools.h"
#include "kernel/consteval.h"
#include "kernel/log.h"
#include <sstream>
#include <stdlib.h>
#include <stdio.h>

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

RTLIL::SigSpec find_any_lvalue(const RTLIL::Process *proc)
{
	RTLIL::SigSpec lvalue;

	for (auto sync : proc->syncs)
	for (auto &action : sync->actions)
		if (action.lhs.size() > 0) {
			lvalue = action.lhs;
			lvalue.sort_and_unify();
			break;
		}

	for (auto sync : proc->syncs) {
		RTLIL::SigSpec this_lvalue;
		for (auto &action : sync->actions)
			this_lvalue.append(action.lhs);
		this_lvalue.sort_and_unify();
		RTLIL::SigSpec common_sig = this_lvalue.extract(lvalue);
		if (common_sig.size() > 0)
			lvalue = common_sig;
	}

	return lvalue;
}

// A flop covers both the process it came from and the wires it drives.
void transfer_wire_sources(const SigSpec& sig, Cell* cell, const RTLIL::Process* proc)
{
	std::vector<SrcRef> sources{proc->src_id()};
	for (auto chunk : sig.chunks())
		if (chunk.wire && chunk.wire->src_id() != SrcRef::Null)
			sources.push_back(chunk.wire->src_id());
	SrcRef fused = cell->module->design->srcs.merge(std::span<const SrcRef>{sources});
	if (fused != SrcRef::Null)
		cell->set_src_id(fused);
}

void gen_dffsr_complex(RTLIL::Module *mod, RTLIL::SigSpec sig_d, RTLIL::SigSpec sig_q, RTLIL::SigSpec clk, bool clk_polarity,
		std::vector<std::pair<RTLIL::SigSpec, RTLIL::SyncRule*>> &async_rules, RTLIL::Process *proc)
{
	// A signal should be set/cleared if there is a load trigger that is enabled
	// such that the load value is 1/0 and it is the highest priority trigger
	RTLIL::SigSpec sig_sr_set = RTLIL::SigSpec(0, sig_d.size());
	RTLIL::SigSpec sig_sr_clr = RTLIL::SigSpec(0, sig_d.size());

	// Reverse iterate through the rules as the first ones are the highest priority
	// so need to be at the top of the mux trees
	for (auto it = async_rules.crbegin(); it != async_rules.crend(); it++)
	{
		const auto& [sync_value, rule] = *it;
		const auto pos_trig = rule->type == RTLIL::SyncType::ST1 ? rule->signal : mod->Not(NEW_ID, rule->signal);

		// If pos_trig is true, we have priority at this point in the tree so
		// set a bit if sync_value has a set bit. Otherwise, defer to the rest
		// of the priority tree
		sig_sr_set = mod->Mux(NEW_ID, sig_sr_set, sync_value, pos_trig);

		// Same deal with clear bit
		const auto sync_value_inv = mod->Not(NEW_ID, sync_value);
		sig_sr_clr = mod->Mux(NEW_ID, sig_sr_clr, sync_value_inv, pos_trig);
	}

	std::stringstream sstr;
	sstr << "$procdff$" << (autoidx++);

	RTLIL::Cell *cell = mod->addDffsr(sstr.str(), clk, sig_sr_set, sig_sr_clr, sig_d, sig_q, clk_polarity);
	cell->attributes = proc->attributes;
	transfer_wire_sources(sig_q, cell, proc);

	log("  created %s cell `%s' with %s edge clock and multiple level-sensitive resets.\n",
			cell->type, cell->name, clk_polarity ? "positive" : "negative");
}

void gen_aldff(RTLIL::Module *mod, RTLIL::SigSpec sig_in, RTLIL::SigSpec sig_set, RTLIL::SigSpec sig_out,
		bool clk_polarity, bool set_polarity, RTLIL::SigSpec clk, RTLIL::SigSpec set, RTLIL::Process *proc)
{
	std::stringstream sstr;
	sstr << "$procdff$" << (autoidx++);

	RTLIL::Cell *cell = mod->addCell(sstr.str(), ID($aldff));
	cell->attributes = proc->attributes;
	transfer_wire_sources(sig_out, cell, proc);

	cell->parameters[ID::WIDTH] = RTLIL::Const(sig_in.size());
	cell->parameters[ID::ALOAD_POLARITY] = RTLIL::Const(set_polarity, 1);
	cell->parameters[ID::CLK_POLARITY] = RTLIL::Const(clk_polarity, 1);
	cell->setPort(ID::D, sig_in);
	cell->setPort(ID::Q, sig_out);
	cell->setPort(ID::AD, sig_set);
	cell->setPort(ID::CLK, clk);
	cell->setPort(ID::ALOAD, set);

	log("  created %s cell `%s' with %s edge clock and %s level non-const reset.\n", cell->type, cell->name,
			clk_polarity ? "positive" : "negative", set_polarity ? "positive" : "negative");
}

void gen_dff(RTLIL::Module *mod, RTLIL::SigSpec sig_in, RTLIL::Const val_rst, RTLIL::SigSpec sig_out,
		bool clk_polarity, bool arst_polarity, RTLIL::SigSpec clk, RTLIL::SigSpec *arst, RTLIL::Process *proc)
{
	std::stringstream sstr;
	sstr << "$procdff$" << (autoidx++);

	RTLIL::Cell *cell = mod->addCell(sstr.str(), clk.empty() ? ID($ff) : arst ? ID($adff) : ID($dff));
	cell->attributes = proc->attributes;
	transfer_wire_sources(sig_out, cell, proc);

	cell->parameters[ID::WIDTH] = RTLIL::Const(sig_in.size());
	if (arst) {
		cell->parameters[ID::ARST_POLARITY] = RTLIL::Const(arst_polarity, 1);
		cell->parameters[ID::ARST_VALUE] = val_rst;
	}
	if (!clk.empty()) {
		cell->parameters[ID::CLK_POLARITY] = RTLIL::Const(clk_polarity, 1);
	}

	cell->setPort(ID::D, sig_in);
	cell->setPort(ID::Q, sig_out);
	if (arst)
		cell->setPort(ID::ARST, *arst);
	if (!clk.empty())
		cell->setPort(ID::CLK, clk);

	if (!clk.empty())
		log("  created %s cell `%s' with %s edge clock", cell->type, cell->name, clk_polarity ? "positive" : "negative");
	else
		log("  created %s cell `%s' with global clock", cell->type, cell->name);
	if (arst)
		log(" and %s level reset", arst_polarity ? "positive" : "negative");
	log(".\n");
}

static void error_at_src(const RTLIL::Design *design, SrcRef src, const std::string &msg)
{
	if (src == SrcRef::Null)
		log_error("%s\n", msg.c_str());
	else
		log_error("%s: %s\n", design->srcs.str(src).c_str(), msg.c_str());
}

static void error_at_proc(const RTLIL::Process *proc, const std::string &msg)
{
	error_at_src(proc->module->design, proc->src_id(), msg);
}

void proc_dff(RTLIL::Module *mod, RTLIL::Process *proc, ConstEval &ce)
{
	while (1)
	{
		RTLIL::SigSpec sig = find_any_lvalue(proc);

		if (sig.size() == 0)
			break;

		log("Creating register for signal `%s.%s' using process `%s.%s'.\n",
				mod->name, log_signal(sig), mod->name, proc->name);

		RTLIL::SigSpec insig = RTLIL::SigSpec(RTLIL::State::Sz, sig.size());
		RTLIL::SyncRule *sync_edge = NULL;
		RTLIL::SyncRule *sync_always = NULL;
		bool global_clock = false;

		// A priority ordered set of rules, pairing the value to be assigned for
		// that rule to the rule
		std::vector<std::pair<RTLIL::SigSpec, RTLIL::SyncRule*>> async_rules;

		// Needed when the async rules are collapsed into one as async_rules
		// works with pointers to SyncRule
		RTLIL::SyncRule single_async_rule;

		for (auto sync : proc->syncs)
		for (auto &action : sync->actions)
		{
			if (action.lhs.extract(sig).size() == 0)
				continue;

			if (sync->type == RTLIL::SyncType::ST0 || sync->type == RTLIL::SyncType::ST1) {
				RTLIL::SigSpec rstval = RTLIL::SigSpec(RTLIL::State::Sz, sig.size());
				sig.replace(action.lhs, action.rhs, &rstval);
				async_rules.emplace_back(rstval, sync);
			}
			else if (sync->type == RTLIL::SyncType::STp || sync->type == RTLIL::SyncType::STn) {
				if (sync_edge != NULL && sync_edge != sync)
					error_at_src(mod->design, action.src,
							stringf("Multiple edge sensitive events found for signal %s", log_signal(sig)));
				sig.replace(action.lhs, action.rhs, &insig);
				sync_edge = sync;
			}
			else if (sync->type == RTLIL::SyncType::STa) {
				if (sync_always != NULL && sync_always != sync)
					error_at_proc(proc, stringf("Multiple always events found for signal %s", log_signal(sig)));
				sig.replace(action.lhs, action.rhs, &insig);
				sync_always = sync;
			}
			else if (sync->type == RTLIL::SyncType::STg) {
				sig.replace(action.lhs, action.rhs, &insig);
				global_clock = true;
			}
			else {
				error_at_proc(proc, stringf("Event with any-edge sensitivity found for signal %s", log_signal(sig)));
			}

			action.lhs.remove2(sig, &action.rhs);
		}

		// If all async rules assign the same value, priority ordering between
		// them doesn't matter so they can be collapsed together into one rule
		// with the disjunction of triggers
		if (!async_rules.empty() &&
		    std::all_of(async_rules.begin(), async_rules.end(), [&](auto& p) {
		        return p.first == async_rules.front().first;
		    }))
		{
			const auto rstval = async_rules.front().first;

			// The trigger is the disjunction of existing triggers
			// (with appropriate negation)
			RTLIL::SigSpec triggers;
			for (const auto &[_, it] : async_rules)
				triggers.append(it->type == RTLIL::SyncType::ST1 ? it->signal : mod->Not(NEW_ID, it->signal));

			// Put this into the dummy sync rule so it can be treated the same
			// as ones coming from the module
			single_async_rule.type = RTLIL::SyncType::ST1;
			single_async_rule.signal = mod->ReduceOr(NEW_ID, triggers);
			// TODO
			single_async_rule.actions.push_back({sig, rstval});

			// Replace existing rules with this new rule
			async_rules.clear();
			async_rules.emplace_back(rstval, &single_async_rule);
		}

		SigSpec sig_q = sig;
		ce.assign_map.apply(insig);
		ce.assign_map.apply(sig);

		// If the reset value assigns the reg to itself, add this as part of
		// the input signal and delete the rule
		if (async_rules.size() == 1 && async_rules.front().first == sig) {
			const auto& [_, rule] = async_rules.front();
			if (rule->type == RTLIL::SyncType::ST1)
				insig = mod->Mux(NEW_ID, insig, sig, rule->signal);
			else
				insig = mod->Mux(NEW_ID, sig, insig, rule->signal);

			async_rules.clear();
		}

		if (sync_always) {
			if (sync_edge || !async_rules.empty())
				error_at_proc(proc, stringf("Mixed always event with edge and/or level sensitive events for signal %s", log_signal(sig)));
			log("  created direct connection (no actual register cell created).\n");
			mod->connect(RTLIL::SigSig(sig, insig));
			continue;
		}

		if (!sync_edge && !global_clock)
			error_at_proc(proc, stringf("Missing edge-sensitive event for signal %s", log_signal(sig)));

		// More than one reset value so we derive a dffsr formulation
		if (async_rules.size() > 1)
		{
			log_warning("Complex async reset for dff `%s'.\n", log_signal(sig));
			gen_dffsr_complex(mod, insig, sig, sync_edge->signal, sync_edge->type == RTLIL::SyncType::STp, async_rules, proc);
			continue;
		}

		// If there is a reset condition in the async rules, use it
		SigSpec rstval = async_rules.empty() ? RTLIL::SigSpec(RTLIL::State::Sz, sig.size()) : async_rules.front().first;
		RTLIL::SyncRule* sync_level = async_rules.empty() ? nullptr : async_rules.front().second;
		ce.assign_map.apply(rstval);

		if (!rstval.is_fully_const() && !ce.eval(rstval))
		{
			log_warning("Async reset value `%s' is not constant!\n", log_signal(rstval));
			gen_aldff(mod, insig, rstval, sig_q,
					sync_edge->type == RTLIL::SyncType::STp,
					sync_level && sync_level->type == RTLIL::SyncType::ST1,
					sync_edge->signal, sync_level->signal, proc);
			continue;
		}

		gen_dff(mod, insig, rstval.as_const(), sig_q,
				sync_edge && sync_edge->type == RTLIL::SyncType::STp,
				sync_level && sync_level->type == RTLIL::SyncType::ST1,
				sync_edge ? sync_edge->signal : SigSpec(),
				sync_level ? &sync_level->signal : NULL, proc);
	}
}

struct ProcDffPass : public Pass {
	ProcDffPass() : Pass("proc_dff", "extract flip-flops from processes") { }
	void help() override
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    proc_dff [selection]\n");
		log("\n");
		log("This pass identifies flip-flops in the processes and converts them to\n");
		log("d-type flip-flop cells.\n");
		log("\n");
	}
	void execute(std::vector<std::string> args, RTLIL::Design *design) override
	{
		log_header(design, "Executing PROC_DFF pass (convert process syncs to FFs).\n");

		extra_args(args, 1, design);

		for (auto mod : design->all_selected_modules()) {
			ConstEval ce(mod);
			for (auto proc : mod->selected_processes())
				proc_dff(mod, proc, ce);
		}
	}
} ProcDffPass;

PRIVATE_NAMESPACE_END