clockgate: centralize clock enables out of FFs

passes/techmap/Makefile.inc

@@ -49,6 +49,7 @@ OBJS += passes/techmap/dffunmap.o
 OBJS += passes/techmap/flowmap.o
 OBJS += passes/techmap/extractinv.o
 OBJS += passes/techmap/cellmatch.o
+OBJS += passes/techmap/clockgate.o
 endif
 
 ifeq ($(DISABLE_SPAWN),0)

passes/techmap/clockgate.cc

@@ -0,0 +1,230 @@
+#include "kernel/yosys.h"
+#include "kernel/ff.h"
+#include <optional>
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct ClockGateCell {
+	IdString name;
+	IdString ce_pin;
+	IdString clk_in_pin;
+	IdString clk_out_pin;
+};
+
+ClockGateCell icg_from_arg(std::string& name, std::string& str) {
+	ClockGateCell c;
+	c.name = RTLIL::escape_id(name);
+	char delimiter = ':';
+	size_t pos1 = str.find(delimiter);
+	if (pos1 == std::string::npos)
+		log_cmd_error("Not enough ports in descriptor string");
+	size_t pos2 = str.find(delimiter, pos1 + 1);
+	if (pos2 == std::string::npos)
+		log_cmd_error("Not enough ports in descriptor string");
+	size_t pos3 = str.find(delimiter, pos2 + 1);
+	if (pos3 != std::string::npos)
+		log_cmd_error("Too many ports in descriptor string");
+
+	std::string ce = str.substr(0, pos1);
+	c.ce_pin = RTLIL::escape_id(ce);
+
+	std::string clk_in = str.substr(pos1 + 1, pos2 - (pos1 + 1));
+	c.clk_in_pin = RTLIL::escape_id(clk_in);
+
+	std::string clk_out = str.substr(pos2 + 1, str.size() - (pos2 + 1));
+	c.clk_out_pin = RTLIL::escape_id(clk_out);
+	return c;
+}
+
+struct ClockgatePass : public Pass {
+	ClockgatePass() : Pass("clockgate", "extract clock gating out of flip flops") { }
+	void help() override {
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    clockgate [options] [selection]\n");
+		log("\n");
+		log("Creates gated clock nets for sets of FFs with clock enable\n");
+		log("sharing a clock and replaces the FFs with versions without\n");
+		log("clock enable inputs. Intended to reduce power consumption\n");
+		log("in ASIC designs.\n");
+		log("\n");
+		log("    -pos <celltype> <ce>:<clk>:<gclk>\n");
+		log("        If specified, rising-edge FFs will have CE inputs\n");
+		log("        removed and a gated clock will be created by the\n");
+		log("        user-specified <celltype> ICG (integrated clock gating)\n");
+		log("        cell with ports named <ce>, <clk>, <gclk>.\n");
+		log("        The ICG's clock enable pin must be active high.\n");
+		log("    -neg <celltype> <ce>:<clk>:<gclk>\n");
+		log("        If specified, falling-edge FFs will have CE inputs\n");
+		log("        removed and a gated clock will be created by the\n");
+		log("        user-specified <celltype> ICG (integrated clock gating)\n");
+		log("        cell with ports named <ce>, <clk>, <gclk>.\n");
+		log("        The ICG's clock enable pin must be active high.\n");
+		log("    -tie_lo <port_name>\n");
+		log("        Port <port_name> of the ICG will be tied to zero.\n");
+		log("        Intended for DFT scan-enable pins.\n");
+		log("    -min_net_size <n>\n");
+		log("        Only work on clocks with at least <n> eligible FFs.\n");
+		// log("        \n");
+	}
+
+	SigMap sigmap;
+	FfInitVals initvals;
+
+	// One ICG will be generated per ClkNetInfo
+	// if the number of FFs associated with it is sufficent
+	struct ClkNetInfo {
+		// Original, ungated clock into enabled FF
+		Wire* clk_net;
+		// Original clock enable into enabled FF
+		Wire* ce_net;
+		bool pol_clk;
+		bool pol_ce;
+		unsigned int hash() const {
+			auto t = std::make_tuple(clk_net, ce_net, pol_clk, pol_ce);
+			unsigned int h = mkhash_init;
+			h = mkhash(h, hash_ops<decltype(t)>::hash(t));
+			return h;
+		}
+		bool operator==(const ClkNetInfo& other) const {
+			return (clk_net == other.clk_net) &&
+			       (ce_net == other.ce_net) &&
+			       (pol_clk == other.pol_clk) &&
+			       (pol_ce == other.pol_ce);
+		}
+	};
+
+	struct GClkNetInfo {
+		// How many CE FFs on this CLK net have we seen?
+		int net_size;
+		// After ICG generation, we have new gated CLK signals
+		Wire* new_net;
+	};
+
+	ClkNetInfo clk_info_from_ff(FfData& ff) {
+		Wire* clk = ff.sig_clk.as_wire();
+		Wire* ce = ff.sig_ce.as_wire();
+		ClkNetInfo info{clk, ce, ff.pol_clk, ff.pol_ce};
+		return info;
+	}
+
+	void execute(std::vector<std::string> args, RTLIL::Design *design) override {
+		log_header(design, "Executing CLOCK_GATE pass (extract clock gating out of flip flops).\n");
+
+		std::optional<ClockGateCell> pos_icg_desc;
+		std::optional<ClockGateCell> neg_icg_desc;
+		std::vector<std::string> tie_lo_ports;
+		int min_net_size = 0;
+
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			if (args[argidx] == "-pos" && argidx+2 < args.size()) {
+				auto name = args[++argidx];
+				auto rest = args[++argidx];
+				pos_icg_desc = icg_from_arg(name, rest);
+			}
+			if (args[argidx] == "-neg" && argidx+2 < args.size()) {
+				auto name = args[++argidx];
+				auto rest = args[++argidx];
+				neg_icg_desc = icg_from_arg(name, rest);
+			}
+			if (args[argidx] == "-tie_lo" && argidx+1 < args.size()) {
+				tie_lo_ports.push_back(RTLIL::escape_id(args[++argidx]));
+			}
+			if (args[argidx] == "-min_net_size" && argidx+1 < args.size()) {
+				min_net_size = atoi(args[++argidx].c_str());
+			}
+		}
+
+		extra_args(args, argidx, design);
+
+		pool<Cell*> ce_ffs;
+		dict<ClkNetInfo, GClkNetInfo> clk_nets;
+
+		int gated_flop_count = 0;
+		for (auto module : design->selected_whole_modules()) {
+			sigmap.set(module);
+			initvals.set(&sigmap, module);
+			for (auto cell : module->cells()) {
+				if (!RTLIL::builtin_ff_cell_types().count(cell->type))
+					continue;
+
+				FfData ff(&initvals, cell);
+				// It would be odd to get constants, but we better handle it
+				if (ff.has_ce && ff.sig_clk.is_wire() && ff.sig_ce.is_wire()) {
+					ce_ffs.insert(cell);
+
+					ClkNetInfo info = clk_info_from_ff(ff);
+					auto it = clk_nets.find(info);
+					if (it == clk_nets.end())
+						clk_nets[info] = GClkNetInfo();
+					clk_nets[info].net_size++;
+				}
+			}
+
+			for (auto& clk_net : clk_nets) {
+				log_debug("checking clk net %s\n", clk_net.first.clk_net->name.c_str());
+				auto& clk = clk_net.first;
+				auto& gclk = clk_net.second;
+
+				if (gclk.net_size < min_net_size)
+					continue;
+
+				std::optional<ClockGateCell> matching_icg_desc;
+
+				if (pos_icg_desc && clk.pol_clk)
+					matching_icg_desc = pos_icg_desc;
+				else if (neg_icg_desc && !clk.pol_clk)
+					matching_icg_desc = neg_icg_desc;
+
+				if (!matching_icg_desc)
+					continue;
+
+				log_debug("building ICG for clk net %s\n", clk_net.first.clk_net->name.c_str());
+				Cell* icg = module->addCell(NEW_ID, matching_icg_desc->name);
+				icg->setPort(matching_icg_desc->ce_pin, clk.ce_net);
+				icg->setPort(matching_icg_desc->clk_in_pin, clk.clk_net);
+				gclk.new_net = module->addWire(NEW_ID);
+				icg->setPort(matching_icg_desc->clk_out_pin, gclk.new_net);
+				// Tie low DFT ports like scan chain enable
+				for (auto port : tie_lo_ports)
+					icg->setPort(port, Const(0));
+				// Fix CE polarity if needed
+				if (!clk.pol_ce) {
+					SigBit ce_fixed_pol = module->NotGate(NEW_ID, clk.ce_net);
+					icg->setPort(matching_icg_desc->ce_pin, ce_fixed_pol);
+				}
+			}
+
+			for (auto cell : ce_ffs) {
+				FfData ff(&initvals, cell);
+				ClkNetInfo info = clk_info_from_ff(ff);
+				auto it = clk_nets.find(info);
+				log_assert(it != clk_nets.end() && "Bug: desync ce_ffs and clk_nets");
+
+				if (!it->second.new_net)
+					continue;
+
+				log_debug("Fix up FF %s\n", cell->name.c_str());
+				// Now we start messing with the design
+				ff.has_ce = false;
+				// Construct the clock gate
+				// ICG = integrated clock gate, industry shorthand
+				ff.sig_clk = (*it).second.new_net;
+
+				// Rebuild the flop
+				(void)ff.emit();
+
+				gated_flop_count++;
+			}
+			ce_ffs.clear();
+			clk_nets.clear();
+		}
+
+		log("Converted %d FFs.\n", gated_flop_count);
+    }
+} ClockgatePass;
+
+
+PRIVATE_NAMESPACE_END