Add shregmap -init_msb_first and use in synth_xilinx

2 files changed, 16 insertions, 4 deletions

diff --git a/passes/techmap/shregmap.cc b/passes/techmap/shregmap.cc
index f20863ba0..6cd9082dc 100644
--- a/passes/techmap/shregmap.cc
+++ b/passes/techmap/shregmap.cc
@@ -34,7 +34,7 @@ struct ShregmapOptions
 {
 	int minlen, maxlen;
 	int keep_before, keep_after;
-	bool zinit, init, params, ffe;
+	bool zinit, init, params, ffe, init_msb_first;
 	dict<IdString, pair<IdString, IdString>> ffcells;
 	ShregmapTech *tech;
 
@@ -48,6 +48,7 @@ struct ShregmapOptions
 		init = false;
 		params = false;
 		ffe = false;
+		init_msb_first = false;
 		tech = nullptr;
 	}
 };
@@ -307,6 +308,8 @@ struct ShregmapWorker
 						initval.push_back(State::S0);
 					remove_init.insert(bit);
 				}
+				if (opts.init_msb_first)
+					std::reverse(initval.begin(), initval.end());
 				first_cell->setParam("\\INIT", initval);
 			}
 
@@ -442,9 +445,13 @@ struct ShregmapPass : public Pass {
 		log("\n");
 		log("    -init\n");
 		log("        map initialized registers to the shift reg, add an INIT parameter to\n");
-		log("        generated cells with the initialization value. (first bit to shift out\n");
+		log("        generated cells with the initialization value. (First bit to shift out\n");
 		log("        in LSB position)\n");
 		log("\n");
+		log("    -init_msb_first\n");
+		log("        same as -init, but INIT parameter to have first bit to shift out\n");
+		log("        in MSB position.\n");
+		log("\n");
 		log("    -tech greenpak4\n");
 		log("        map to greenpak4 shift registers.\n");
 		log("\n");
@@ -515,6 +522,11 @@ struct ShregmapPass : public Pass {
 				opts.init = true;
 				continue;
 			}
+			if (args[argidx] == "-init_msb_first") {
+				opts.init = true;
+				opts.init_msb_first = true;
+				continue;
+			}
 			if (args[argidx] == "-params") {
 				opts.params = true;
 				continue;
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index ce597ea4a..71b468e38 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -105,7 +105,7 @@ struct SynthXilinxPass : public Pass
 		log("        dff2dffe\n");
 		log("        opt -full\n");
 		log("        techmap -map +/techmap.v -map +/xilinx/arith_map.v\n");
-		log("        shregmap -init -params -enpol any_or_none\n");
+		log("        shregmap -init_msb_first -params -enpol any_or_none\n");
 		log("        opt -fast\n");
 		log("\n");
 		log("    map_luts:\n");
@@ -225,7 +225,7 @@ struct SynthXilinxPass : public Pass
 			Pass::call(design, "dff2dffe");
 			Pass::call(design, "opt -full");
 			Pass::call(design, "techmap -map +/techmap.v -map +/xilinx/arith_map.v");
-			Pass::call(design, "shregmap -init -params -enpol any_or_none");
+			Pass::call(design, "shregmap -init_msb_first -params -enpol any_or_none");
 			Pass::call(design, "opt -fast");
 		}