Restored simplified Verilog version of delay.sv

Author: pConst

delay.sv

@@ -26,17 +26,17 @@
 /* --- INSTANTIATION TEMPLATE BEGIN ---
 
 delay #(
-    .LENGTH( 2 ),
-    .WIDTH( 1 ),
-    .TYPE( "CELLS" ),
-    .REGISTER_OUTPUTS( "FALSE" )
+  .LENGTH( 2 ),
+  .WIDTH( 1 ),
+  .TYPE( "CELLS" ),
+  .REGISTER_OUTPUTS( "FALSE" )
 ) S1 (
-    .clk( clk ),
-    .nrst( 1'b1 ),
-    .ena( 1'b1 ),
+  .clk( clk ),
+  .nrst( 1'b1 ),
+  .ena( 1'b1 ),
 
-    .in(  ),
-    .out(  )
+  .in(  ),
+  .out(  )
 );
 
 --- INSTANTIATION TEMPLATE END ---*/
@@ -209,3 +209,4 @@ generate
 endgenerate
 
 endmodule
+

delay.v

@@ -0,0 +1,69 @@
+//------------------------------------------------------------------------------
+// delay.v
+// published as part of https://github.com/pConst/basic_verilog
+// Konstantin Pavlov, [email protected]
+//------------------------------------------------------------------------------
+
+// INFO -------------------------------------------------------------------------
+// Static Delay for arbitrary signal
+// (simplified Verilog version, see ./delay.sv for advanced features)
+//
+// Another equivalent names for this module:
+//          conveyor.sv
+//          synchronizer.sv
+//
+// Tip for Xilinx-based implementations: Leave nrst=1'b1 and ena=1'b1 on
+// purpose of inferring Xilinx`s SRL16E/SRL32E primitives
+//
+// CAUTION: delay module is widely used for synchronizing signals across clock
+//   domains. When synchronizing, please exclude input data paths from timing
+//   analysis manually by writing appropriate set_false_path SDC constraint
+//
+
+/* --- INSTANTIATION TEMPLATE BEGIN ---
+
+delay S1 #(
+  .LENGTH( 2 ),
+  .WIDTH( 1 )
+)(
+  .clk( clk ),
+  .nrst( 1'b1 ),
+  .ena( 1'b1 ),
+
+  .in(  ),
+  .out(  )
+);
+
+--- INSTANTIATION TEMPLATE END ---*/
+
+
+module delay #( parameter
+  LENGTH = 2,                  // delay/synchronizer chain length
+  WIDTH = 1                    // signal width
+)(
+  input clk,
+  input nrst,
+  input ena,
+
+  input [WIDTH-1:0] in,
+  output [WIDTH-1:0] out
+);
+
+  reg [LENGTH:1][WIDTH-1:0] data = 0;
+
+  always @(posedge clk) begin
+    integer i;
+    if( ~nrst ) begin
+      data <= 0;
+    end else if( ena ) begin
+      for( i=LENGTH-1; i>0; i=i-1 ) begin
+        data[i+1][WIDTH-1:0] <= data[i][WIDTH-1:0];
+      end
+      data[1][WIDTH-1:0] <= in[WIDTH-1:0];
+    end
+  end
+
+  assign out[WIDTH-1:0] = data[LENGTH][WIDTH-1:0];
+
+endmodule
+