diff --git a/.github/issue_template.md b/.github/issue_template.md
index 24e91a4e7..4563a71de 100644
--- a/.github/issue_template.md
+++ b/.github/issue_template.md
@@ -1,7 +1,7 @@
 ## Steps to reproduce the issue
 
 *Provide instructions for reproducing the issue. Make sure to include
-all neccessary source files. (You can simply drag&drop a .zip file into
+all necessary source files. (You can simply drag&drop a .zip file into
 the issue editor.)*
 
 ## Expected behavior
diff --git a/backends/edif/edif.cc b/backends/edif/edif.cc
index 5f9ec54fd..d4e56a9eb 100644
--- a/backends/edif/edif.cc
+++ b/backends/edif/edif.cc
@@ -106,6 +106,9 @@ struct EdifBackend : public Backend {
 		log("        if the design contains constant nets. use \"hilomap\" to map to custom\n");
 		log("        constant drivers first)\n");
 		log("\n");
+		log("    -attrprop\n");
+		log("        create EDIF properties for cell attributes\n");
+		log("\n");
 		log("    -pvector {par|bra|ang}\n");
 		log("        sets the delimiting character for module port rename clauses to\n");
 		log("        parentheses, square brackets, or angle brackets.\n");
@@ -121,6 +124,7 @@ struct EdifBackend : public Backend {
 		log_header(design, "Executing EDIF backend.\n");
 		std::string top_module_name;
 		bool port_rename = false;
+		bool attr_properties = false;
 		std::map<RTLIL::IdString, std::map<RTLIL::IdString, int>> lib_cell_ports;
 		bool nogndvcc = false;
 		CellTypes ct(design);
@@ -137,6 +141,10 @@ struct EdifBackend : public Backend {
 				nogndvcc = true;
 				continue;
 			}
+			if (args[argidx] == "-attrprop") {
+				attr_properties = true;
+				continue;
+			}
 			if (args[argidx] == "-pvector" && argidx+1 < args.size()) {
 				std::string parray;
 				port_rename = true;
@@ -332,24 +340,33 @@ struct EdifBackend : public Backend {
 				*f << stringf("          (instance %s\n", EDIF_DEF(cell->name));
 				*f << stringf("            (viewRef VIEW_NETLIST (cellRef %s%s))", EDIF_REF(cell->type),
 						lib_cell_ports.count(cell->type) > 0 ? " (libraryRef LIB)" : "");
-				for (auto &p : cell->parameters)
-					if ((p.second.flags & RTLIL::CONST_FLAG_STRING) != 0)
-						*f << stringf("\n            (property %s (string \"%s\"))", EDIF_DEF(p.first), p.second.decode_string().c_str());
-					else if (p.second.bits.size() <= 32 && RTLIL::SigSpec(p.second).is_fully_def())
-						*f << stringf("\n            (property %s (integer %u))", EDIF_DEF(p.first), p.second.as_int());
+
+				auto add_prop = [&](IdString name, Const val) {
+					if ((val.flags & RTLIL::CONST_FLAG_STRING) != 0)
+						*f << stringf("\n            (property %s (string \"%s\"))", EDIF_DEF(name), val.decode_string().c_str());
+					else if (val.bits.size() <= 32 && RTLIL::SigSpec(val).is_fully_def())
+						*f << stringf("\n            (property %s (integer %u))", EDIF_DEF(name), val.as_int());
 					else {
 						std::string hex_string = "";
-						for (size_t i = 0; i < p.second.bits.size(); i += 4) {
+						for (size_t i = 0; i < val.bits.size(); i += 4) {
 							int digit_value = 0;
-							if (i+0 < p.second.bits.size() && p.second.bits.at(i+0) == RTLIL::State::S1) digit_value |= 1;
-							if (i+1 < p.second.bits.size() && p.second.bits.at(i+1) == RTLIL::State::S1) digit_value |= 2;
-							if (i+2 < p.second.bits.size() && p.second.bits.at(i+2) == RTLIL::State::S1) digit_value |= 4;
-							if (i+3 < p.second.bits.size() && p.second.bits.at(i+3) == RTLIL::State::S1) digit_value |= 8;
+							if (i+0 < val.bits.size() && val.bits.at(i+0) == RTLIL::State::S1) digit_value |= 1;
+							if (i+1 < val.bits.size() && val.bits.at(i+1) == RTLIL::State::S1) digit_value |= 2;
+							if (i+2 < val.bits.size() && val.bits.at(i+2) == RTLIL::State::S1) digit_value |= 4;
+							if (i+3 < val.bits.size() && val.bits.at(i+3) == RTLIL::State::S1) digit_value |= 8;
 							char digit_str[2] = { "0123456789abcdef"[digit_value], 0 };
 							hex_string = std::string(digit_str) + hex_string;
 						}
-						*f << stringf("\n            (property %s (string \"%d'h%s\"))", EDIF_DEF(p.first), GetSize(p.second.bits), hex_string.c_str());
+						*f << stringf("\n            (property %s (string \"%d'h%s\"))", EDIF_DEF(name), GetSize(val.bits), hex_string.c_str());
 					}
+				};
+
+				for (auto &p : cell->parameters)
+					add_prop(p.first, p.second);
+				if (attr_properties)
+					for (auto &p : cell->attributes)
+						add_prop(p.first, p.second);
+
 				*f << stringf(")\n");
 				for (auto &p : cell->connections()) {
 					RTLIL::SigSpec sig = sigmap(p.second);
diff --git a/frontends/verific/verific.cc b/frontends/verific/verific.cc
index c5fa58313..dba3b0f0c 100644
--- a/frontends/verific/verific.cc
+++ b/frontends/verific/verific.cc
@@ -118,6 +118,18 @@ RTLIL::SigBit VerificImporter::net_map_at(Net *net)
 	return net_map.at(net);
 }
 
+bool is_blackbox(Netlist *nl)
+{
+	if (nl->IsBlackBox())
+		return true;
+
+	const char *attr = nl->GetAttValue("blackbox");
+	if (attr != nullptr && strcmp(attr, "0"))
+		return true;
+
+	return false;
+}
+
 void VerificImporter::import_attributes(dict<RTLIL::IdString, RTLIL::Const> &attributes, DesignObj *obj)
 {
 	MapIter mi;
@@ -709,7 +721,7 @@ void VerificImporter::import_netlist(RTLIL::Design *design, Netlist *nl, std::se
 	netlist = nl;
 
 	if (design->has(module_name)) {
-		if (!nl->IsOperator())
+		if (!nl->IsOperator() && !is_blackbox(nl))
 			log_cmd_error("Re-definition of module `%s'.\n", nl->Owner()->Name());
 		return;
 	}
@@ -718,7 +730,7 @@ void VerificImporter::import_netlist(RTLIL::Design *design, Netlist *nl, std::se
 	module->name = module_name;
 	design->add(module);
 
-	if (nl->IsBlackBox()) {
+	if (is_blackbox(nl)) {
 		log("Importing blackbox module %s.\n", RTLIL::id2cstr(module->name));
 		module->set_bool_attribute("\\blackbox");
 	} else {
@@ -1676,6 +1688,7 @@ YOSYS_NAMESPACE_END
 
 PRIVATE_NAMESPACE_BEGIN
 
+#ifdef YOSYS_ENABLE_VERIFIC
 bool check_noverific_env()
 {
 	const char *e = getenv("YOSYS_NOVERIFIC");
@@ -1685,6 +1698,7 @@ bool check_noverific_env()
 		return false;
 	return true;
 }
+#endif
 
 struct VerificPass : public Pass {
 	VerificPass() : Pass("verific", "load Verilog and VHDL designs using Verific") { }
diff --git a/kernel/celltypes.h b/kernel/celltypes.h
index fcc4fcc4b..6041168bb 100644
--- a/kernel/celltypes.h
+++ b/kernel/celltypes.h
@@ -157,7 +157,7 @@ struct CellTypes
 		IdString A = "\\A", B = "\\B", C = "\\C", D = "\\D";
 		IdString E = "\\E", F = "\\F", G = "\\G", H = "\\H";
 		IdString I = "\\I", J = "\\J", K = "\\K", L = "\\L";
-		IdString M = "\\I", N = "\\N", O = "\\O", P = "\\P";
+		IdString M = "\\M", N = "\\N", O = "\\O", P = "\\P";
 		IdString S = "\\S", T = "\\T", U = "\\U", V = "\\V";
 		IdString Y = "\\Y";
 
diff --git a/techlibs/xilinx/cells_xtra.sh b/techlibs/xilinx/cells_xtra.sh
index c7ad16043..e7c7d17bf 100644
--- a/techlibs/xilinx/cells_xtra.sh
+++ b/techlibs/xilinx/cells_xtra.sh
@@ -1,13 +1,13 @@
 #!/bin/bash
 
 set -e
-libdir="/opt/Xilinx/Vivado/2015.4/data/verilog/src"
+libdir="/opt/Xilinx/Vivado/2018.1/data/verilog/src"
 
 function xtract_cell_decl()
 {
 	for dir in $libdir/xeclib $libdir/retarget; do
 		[ -f $dir/$1.v ] || continue
-		egrep '^\s*((end)?module|parameter|input|output|(end)?function|(end)?task)' $dir/$1.v |
+		egrep '^\s*((end)?module|parameter|input|inout|output|(end)?function|(end)?task)' $dir/$1.v |
 			sed -re '/UNPLACED/ d; /^\s*function/,/endfunction/ d; /^\s*task/,/endtask/ d;
 			         s,//.*,,; s/#?\(.*/(...);/; s/^(input|output|parameter)/ \1/;
 			         s/\s+$//; s/,$/;/; /input|output|parameter/ s/[^;]$/&;/; s/\s+/ /g;
diff --git a/techlibs/xilinx/cells_xtra.v b/techlibs/xilinx/cells_xtra.v
index a2dd01ad5..69e54233a 100644
--- a/techlibs/xilinx/cells_xtra.v
+++ b/techlibs/xilinx/cells_xtra.v
@@ -2225,6 +2225,7 @@ module IOBUF (...);
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
     output O;
+    inout IO;
     input I, T;
 endmodule
 
@@ -2236,6 +2237,7 @@ module IOBUF_DCIEN (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    inout IO;
     input DCITERMDISABLE;
     input I;
     input IBUFDISABLE;
@@ -2250,6 +2252,7 @@ module IOBUF_INTERMDISABLE (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    inout IO;
     input I;
     input IBUFDISABLE;
     input INTERMDISABLE;
@@ -2263,6 +2266,7 @@ module IOBUFDS (...);
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
     output O;
+    inout IO, IOB;
     input I, T;
 endmodule
 
@@ -2275,6 +2279,8 @@ module IOBUFDS_DCIEN (...);
     parameter SLEW = "SLOW";
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
+    inout IO;
+    inout IOB;
     input DCITERMDISABLE;
     input I;
     input IBUFDISABLE;
@@ -2288,6 +2294,8 @@ module IOBUFDS_DIFF_OUT (...);
     parameter IOSTANDARD = "DEFAULT";
     output O;
     output OB;
+    inout IO;
+    inout IOB;
     input I;
     input TM;
     input TS;
@@ -2302,6 +2310,8 @@ module IOBUFDS_DIFF_OUT_DCIEN (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    inout IO;
+    inout IOB;
     input DCITERMDISABLE;
     input I;
     input IBUFDISABLE;
@@ -2318,6 +2328,8 @@ module IOBUFDS_DIFF_OUT_INTERMDISABLE (...);
     parameter USE_IBUFDISABLE = "TRUE";
     output O;
     output OB;
+    inout IO;
+    inout IOB;
     input I;
     input IBUFDISABLE;
     input INTERMDISABLE;
@@ -2381,6 +2393,7 @@ module ISERDESE2 (...);
 endmodule
 
 module KEEPER (...);
+    inout O;
 endmodule
 
 module LDCE (...);