2 files changed, 23 insertions, 2 deletions
diff --git a/techlibs/common/simcells.v b/techlibs/common/simcells.v
index c4f170a3c..e770c5453 100644
--- a/techlibs/common/simcells.v
+++ b/techlibs/common/simcells.v
@@ -495,6 +495,23 @@ always @(posedge S, posedge R) begin
 end
 endmodule
 
+`ifdef SIMCELLS_FF
+//  |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+//-
+//-     $_FF_ (D, Q)
+//-
+//- A D-type flip-flop that is clocked from the implicit global clock. (This cell
+//- type is usually only used in netlists for formal verification.)
+//-
+module \$_FF_ (D, Q);
+input D;
+output reg Q;
+always @($global_clock) begin
+	Q <= D;
+end
+endmodule
+`endif
+
 //  |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
 //-
 //-     $_DFF_N_ (D, C, Q)
diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v
index db818269b..b10c858f2 100644
--- a/techlibs/common/simlib.v
+++ b/techlibs/common/simlib.v
@@ -1382,18 +1382,22 @@ endmodule
 
 `endif
 // --------------------------------------------------------
+`ifdef SIMLIB_FF
 
 module \$ff (D, Q);
 
 parameter WIDTH = 0;
 
 input [WIDTH-1:0] D;
-output [WIDTH-1:0] Q;
+output reg [WIDTH-1:0] Q;
 
-assign D = Q;
+always @($global_clk) begin
+	Q <= D;
+end
 
 endmodule
 
+`endif
 // --------------------------------------------------------
 
 module \$dff (CLK, D, Q);