yosys/passes/memory/memory_dff.cc

/*
 *  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.
 *
 */

#include "kernel/register.h"
#include "kernel/log.h"
#include <stdlib.h>
#include <assert.h>
#include <sstream>

static void normalize_sig(RTLIL::Module *module, RTLIL::SigSpec &sig)
{
	for (auto &conn : module->connections)
		sig.replace(conn.first, conn.second);
}

static bool find_sig_before_dff(RTLIL::Module *module, RTLIL::SigSpec &sig, RTLIL::SigSpec &clk, bool &clk_polarity, bool after = false)
{
	bool replaced_bits = false;
	normalize_sig(module, sig);
	sig.expand();

	for (size_t i = 0; i < sig.chunks.size(); i++)
	{
		RTLIL::SigChunk &chunk = sig.chunks[i];

		if (chunk.wire == NULL)
			continue;

		for (auto &cell_it : module->cells)
		{
			RTLIL::Cell *cell = cell_it.second;

			if (cell->type != "$dff")
				continue;

			if (clk != RTLIL::SigSpec(RTLIL::State::Sx)) {
				if (cell->connections["\\CLK"] != clk)
					continue;
				if (cell->parameters["\\CLK_POLARITY"].as_bool() != clk_polarity)
					continue;
			}

			RTLIL::SigSpec q_norm = cell->connections[after ? "\\D" : "\\Q"];
			normalize_sig(module, q_norm);

			RTLIL::SigSpec d = q_norm.extract(chunk, &cell->connections[after ? "\\Q" : "\\D"]);
			if (d.width != 1)
				continue;

			assert(d.chunks.size() == 1);
			chunk = d.chunks[0];
			clk = cell->connections["\\CLK"];
			clk_polarity = cell->parameters["\\CLK_POLARITY"].as_bool();
			replaced_bits = true;
			goto replaced_this_bit;
		}

		return false;
	replaced_this_bit:;
	}

	sig.optimize();
	return replaced_bits;
}

static void handle_wr_cell(RTLIL::Module *module, RTLIL::Cell *cell)
{
	log("Checking cell `%s' in module `%s': ", cell->name.c_str(), module->name.c_str());

	RTLIL::SigSpec clk = RTLIL::SigSpec(RTLIL::State::Sx);
	bool clk_polarity = 0;

	RTLIL::SigSpec sig_addr = cell->connections["\\ADDR"];
	if (!find_sig_before_dff(module, sig_addr, clk, clk_polarity)) {
		log("no (compatible) $dff for address input found.\n");
		return;
	}

	RTLIL::SigSpec sig_data = cell->connections["\\DATA"];
	if (!find_sig_before_dff(module, sig_data, clk, clk_polarity)) {
		log("no (compatible) $dff for data input found.\n");
		return;
	}

	RTLIL::SigSpec sig_en = cell->connections["\\EN"];
	if (!find_sig_before_dff(module, sig_en, clk, clk_polarity)) {
		log("no (compatible) $dff for enable input found.\n");
		return;
	}

	cell->connections["\\CLK"] = clk;
	cell->connections["\\ADDR"] = sig_addr;
	cell->connections["\\DATA"] = sig_data;
	cell->connections["\\EN"] = sig_en;
	cell->parameters["\\CLK_ENABLE"] = RTLIL::Const(1);
	cell->parameters["\\CLK_POLARITY"] = RTLIL::Const(clk_polarity);
	log("merged $dff to cell.\n");
}

#if 1
static void handle_rd_cell(RTLIL::Module*, RTLIL::Cell*)
{
	// merging dffs into read ports isn't neccessary for memory_map.
	// we'd loose the information if the register is on the address or
	// data port and wouldn't get any benefits.
}
#else
static void disconnect_dff(RTLIL::Module *module, RTLIL::SigSpec sig)
{
	normalize_sig(module, sig);
	sig.sort_and_unify();

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

	RTLIL::Wire *wire = new RTLIL::Wire;
	wire->name = sstr.str();
	wire->width = sig.width;
	module->wires[wire->name] = wire;

	RTLIL::SigSpec newsig(wire);

	for (auto &cell_it : module->cells) {
		RTLIL::Cell *cell = cell_it.second;
		if (cell->type == "$dff")
			cell->connections["\\Q"].replace(sig, newsig);
	}
}

static void handle_rd_cell(RTLIL::Module *module, RTLIL::Cell *cell)
{
	log("Checking cell `%s' in module `%s': ", cell->name.c_str(), module->name.c_str());

	bool clk_polarity = 0;

	RTLIL::SigSpec clk_addr = RTLIL::SigSpec(RTLIL::State::Sx);
	RTLIL::SigSpec sig_addr = cell->connections["\\ADDR"];
	if (find_sig_before_dff(module, sig_addr, clk_addr, clk_polarity))
	{
		cell->connections["\\CLK"] = clk_addr;
		cell->connections["\\ADDR"] = sig_addr;
		cell->parameters["\\CLK_ENABLE"] = RTLIL::Const(1);
		cell->parameters["\\CLK_POLARITY"] = RTLIL::Const(clk_polarity);
		log("merged address $dff to cell.\n");
		return;
	}

	RTLIL::SigSpec clk_data = RTLIL::SigSpec(RTLIL::State::Sx);
	RTLIL::SigSpec sig_data = cell->connections["\\DATA"];
	if (find_sig_before_dff(module, sig_data, clk_data, clk_polarity, true))
	{
		disconnect_dff(module, sig_data);
		cell->connections["\\CLK"] = clk_data;
		cell->connections["\\DATA"] = sig_data;
		cell->parameters["\\CLK_ENABLE"] = RTLIL::Const(1);
		cell->parameters["\\CLK_POLARITY"] = RTLIL::Const(clk_polarity);
		log("merged data $dff to cell.\n");
		return;
	}

	log("no (compatible) $dff found.\n");
}
#endif

static void handle_module(RTLIL::Design *design, RTLIL::Module *module)
{
	for (auto &cell_it : module->cells) {
		if (!design->selected(module, cell_it.second))
			continue;
		if (cell_it.second->type == "$memwr" && !cell_it.second->parameters["\\CLK_ENABLE"].as_bool())
				handle_wr_cell(module, cell_it.second);
		if (cell_it.second->type == "$memrd" && !cell_it.second->parameters["\\CLK_ENABLE"].as_bool())
				handle_rd_cell(module, cell_it.second);
	}
}

struct MemoryDffPass : public Pass {
	MemoryDffPass() : Pass("memory_dff", "merge input/output DFFs into memories") { }
	virtual void help()
	{
		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
		log("\n");
		log("    memory_dff [selection]\n");
		log("\n");
		log("This pass detects DFFs at memory ports and merges them into the memory port.\n");
		log("I.e. it consumes an asynchronous memory port and the flip-flops at its\n");
		log("interface and yields a synchronous memory port.\n");
		log("\n");
	}
	virtual void execute(std::vector<std::string> args, RTLIL::Design *design) {
		log_header("Executing MEMORY_DFF pass (merging $dff cells to $memrd and $memwr).\n");
		extra_args(args, 1, design);
		for (auto &mod_it : design->modules)
			if (design->selected(mod_it.second))
				handle_module(design, mod_it.second);
	}
} MemoryDffPass;