From 01daa077a2837830914f3d99f351918d690b9093 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Marcelina=20Ko=C5=9Bcielnicka?= <mwk@0x04.net>
Date: Fri, 17 Jun 2022 14:11:04 +0200
Subject: [PATCH] memory_map: Use const drivers instead of FFs for ROMs.

---
 passes/memory/memory_map.cc | 111 +++++++++++++++++++-----------------
 1 file changed, 59 insertions(+), 52 deletions(-)

diff --git a/passes/memory/memory_map.cc b/passes/memory/memory_map.cc
index ca1ca483d..21c7a761e 100644
--- a/passes/memory/memory_map.cc
+++ b/passes/memory/memory_map.cc
@@ -191,6 +191,10 @@ struct MemoryMapWorker
 				data_reg_out[idx] = static_cells_map[addr];
 				count_static++;
 			}
+			else if (mem.wr_ports.empty())
+			{
+				data_reg_out[idx] = init_data.extract(i*mem.width, mem.width);
+			}
 			else
 			{
 				RTLIL::Cell *c = module->addCell(genid(mem.memid, "", addr), ID($dff));
@@ -266,69 +270,72 @@ struct MemoryMapWorker
 
 		log("  read interface: %d $dff and %d $mux cells.\n", count_dff, count_mux);
 
-		for (int i = 0; i < mem.size; i++)
+		if (!mem.wr_ports.empty())
 		{
-			int addr = i + mem.start_offset;
-			int idx = addr & ((1 << abits) - 1);
-			if (static_cells_map.count(addr) > 0)
-				continue;
-
-			RTLIL::SigSpec sig = data_reg_out[idx];
-
-			for (int j = 0; j < GetSize(mem.wr_ports); j++)
+			for (int i = 0; i < mem.size; i++)
 			{
-				auto &port = mem.wr_ports[j];
-				RTLIL::SigSpec wr_addr = port.addr.extract_end(port.wide_log2);
-				RTLIL::Wire *w_seladdr = addr_decode(wr_addr, RTLIL::SigSpec(addr >> port.wide_log2, GetSize(wr_addr)));
+				int addr = i + mem.start_offset;
+				int idx = addr & ((1 << abits) - 1);
+				if (static_cells_map.count(addr) > 0)
+					continue;
 
-				int sub = addr & ((1 << port.wide_log2) - 1);
+				RTLIL::SigSpec sig = data_reg_out[idx];
 
-				int wr_offset = 0;
-				while (wr_offset < mem.width)
+				for (int j = 0; j < GetSize(mem.wr_ports); j++)
 				{
-					int wr_width = 1;
-					RTLIL::SigSpec wr_bit = port.en.extract(wr_offset + sub * mem.width, 1);
-
-					while (wr_offset + wr_width < mem.width) {
-						RTLIL::SigSpec next_wr_bit = port.en.extract(wr_offset + wr_width + sub * mem.width, 1);
-						if (next_wr_bit != wr_bit)
-							break;
-						wr_width++;
-					}
+					auto &port = mem.wr_ports[j];
+					RTLIL::SigSpec wr_addr = port.addr.extract_end(port.wide_log2);
+					RTLIL::Wire *w_seladdr = addr_decode(wr_addr, RTLIL::SigSpec(addr >> port.wide_log2, GetSize(wr_addr)));
 
-					RTLIL::Wire *w = w_seladdr;
+					int sub = addr & ((1 << port.wide_log2) - 1);
 
-					if (wr_bit != State::S1)
+					int wr_offset = 0;
+					while (wr_offset < mem.width)
 					{
-						RTLIL::Cell *c = module->addCell(genid(mem.memid, "$wren", addr, "", j, "", wr_offset), ID($and));
-						c->parameters[ID::A_SIGNED] = RTLIL::Const(0);
-						c->parameters[ID::B_SIGNED] = RTLIL::Const(0);
-						c->parameters[ID::A_WIDTH] = RTLIL::Const(1);
-						c->parameters[ID::B_WIDTH] = RTLIL::Const(1);
-						c->parameters[ID::Y_WIDTH] = RTLIL::Const(1);
-						c->setPort(ID::A, w);
-						c->setPort(ID::B, wr_bit);
-
-						w = module->addWire(genid(mem.memid, "$wren", addr, "", j, "", wr_offset, "$y"));
-						c->setPort(ID::Y, RTLIL::SigSpec(w));
+						int wr_width = 1;
+						RTLIL::SigSpec wr_bit = port.en.extract(wr_offset + sub * mem.width, 1);
+
+						while (wr_offset + wr_width < mem.width) {
+							RTLIL::SigSpec next_wr_bit = port.en.extract(wr_offset + wr_width + sub * mem.width, 1);
+							if (next_wr_bit != wr_bit)
+								break;
+							wr_width++;
+						}
+
+						RTLIL::Wire *w = w_seladdr;
+
+						if (wr_bit != State::S1)
+						{
+							RTLIL::Cell *c = module->addCell(genid(mem.memid, "$wren", addr, "", j, "", wr_offset), ID($and));
+							c->parameters[ID::A_SIGNED] = RTLIL::Const(0);
+							c->parameters[ID::B_SIGNED] = RTLIL::Const(0);
+							c->parameters[ID::A_WIDTH] = RTLIL::Const(1);
+							c->parameters[ID::B_WIDTH] = RTLIL::Const(1);
+							c->parameters[ID::Y_WIDTH] = RTLIL::Const(1);
+							c->setPort(ID::A, w);
+							c->setPort(ID::B, wr_bit);
+
+							w = module->addWire(genid(mem.memid, "$wren", addr, "", j, "", wr_offset, "$y"));
+							c->setPort(ID::Y, RTLIL::SigSpec(w));
+						}
+
+						RTLIL::Cell *c = module->addCell(genid(mem.memid, "$wrmux", addr, "", j, "", wr_offset), ID($mux));
+						c->parameters[ID::WIDTH] = wr_width;
+						c->setPort(ID::A, sig.extract(wr_offset, wr_width));
+						c->setPort(ID::B, port.data.extract(wr_offset + sub * mem.width, wr_width));
+						c->setPort(ID::S, RTLIL::SigSpec(w));
+
+						w = module->addWire(genid(mem.memid, "$wrmux", addr, "", j, "", wr_offset, "$y"), wr_width);
+						c->setPort(ID::Y, w);
+
+						sig.replace(wr_offset, w);
+						wr_offset += wr_width;
+						count_wrmux++;
 					}
-
-					RTLIL::Cell *c = module->addCell(genid(mem.memid, "$wrmux", addr, "", j, "", wr_offset), ID($mux));
-					c->parameters[ID::WIDTH] = wr_width;
-					c->setPort(ID::A, sig.extract(wr_offset, wr_width));
-					c->setPort(ID::B, port.data.extract(wr_offset + sub * mem.width, wr_width));
-					c->setPort(ID::S, RTLIL::SigSpec(w));
-
-					w = module->addWire(genid(mem.memid, "$wrmux", addr, "", j, "", wr_offset, "$y"), wr_width);
-					c->setPort(ID::Y, w);
-
-					sig.replace(wr_offset, w);
-					wr_offset += wr_width;
-					count_wrmux++;
 				}
-			}
 
-			module->connect(RTLIL::SigSig(data_reg_in[idx], sig));
+				module->connect(RTLIL::SigSig(data_reg_in[idx], sig));
+			}
 		}
 
 		log("  write interface: %d write mux blocks.\n", count_wrmux);
-- 
2.30.2