fpga: lib: Pipeline and add clken to ip_hdr_checksum

Adds LATENCY parameter to control the ammount of pieplineing. Adds a
clock enable to control the advance of the pipeline.

Used in xport when calculating new UDP headers for CHDR traffic.


Original-commit: dd9847c5c3c3fac17658b526a7d8894711af086e

lib/packet_proc/ip_hdr_checksum.v

@@ -1,29 +1,56 @@
 //
-// Copyright 2014 Ettus Research LLC
-// Copyright 2018 Ettus Research, a National Instruments Company
+// Copyright 2020 Ettus Research, a National Instruments Brand
 //
 // SPDX-License-Identifier: LGPL-3.0-or-later
 //
-// Compute IP header checksum.  2 cycles of latency.
-module ip_hdr_checksum
-  (input clk, input [159:0] in, output reg [15:0] out);
+// Description: 
+//   Compute IP header checksum.  0-2 cycles of latency.
+//
+// Parameter:
+//   LATENCY : sets how many pipeline stages are inserted
+//     0 - No pipelining
+//     1 - output Flop
+//     2 - output + gen_sum Flop
+//
 
-   wire [18:0] padded [0:9];
-   reg [18:0]  sum_a, sum_b;
+module ip_hdr_checksum #(
+  parameter LATENCY = 2
+) (
+  input clk, input [159:0] in, output reg [15:0] out, input clken
+);
+
+  wire [18:0] padded [0:9];
    
-   genvar     i;
-   generate
-      for(i=0 ; i<10 ; i=i+1)
+  genvar i;
+  generate
+    for(i=0 ; i<10 ; i=i+1)
 	assign padded[i] = {3'b000,in[i*16+15:i*16]};
-   endgenerate
+    endgenerate
 
-   always @(posedge clk)  sum_a = padded[0] + padded[1] + padded[2] + padded[3] + padded[4];
-   always @(posedge clk)  sum_b = padded[5] + padded[6] + padded[7] + padded[8] + padded[9];
+  wire [18:0] sum_a_d, sum_b_d;
+  reg  [18:0] sum_a_q, sum_b_q;
 
-   wire [18:0] sum = sum_a + sum_b;
+  assign sum_a_d = padded[0] + padded[1] + padded[2] + padded[3] + padded[4];
+  assign sum_b_d = padded[5] + padded[6] + padded[7] + padded[8] + padded[9];
+
+  if (LATENCY >= 1) begin : gen_sum_ff
+    always @(posedge clk) if (clken) sum_a_q <= sum_a_d;
+    always @(posedge clk) if (clken) sum_b_q <= sum_b_d;
+  end else begin : gen_sum_comb
+    always @(sum_a_d) sum_a_q = sum_a_d;
+    always @(sum_b_d) sum_b_q = sum_b_d;
+  end
+
+  wire [18:0] sum;
+  wire [15:0] out_d;
+
+  assign sum = sum_a_q + sum_b_q;
+  assign out_d = ~(sum[15:0] + {13'd0,sum[18:16]});
+
+  if (LATENCY >= 2) begin : gen_out_ff
+    always @(posedge clk)  if (clken) out <= out_d;
+  end else begin : gen_out_comb
+    always @(out_d) out = out_d;
+  end
 
-   always @(posedge clk)
-     out <= ~(sum[15:0] + {13'd0,sum[18:16]});
-   
-   
 endmodule // ip_hdr_checksum

lib/packet_proc/ip_hdr_checksum_tb.v

@@ -1,43 +0,0 @@
-//
-// Copyright 2013 Ettus Research, a National Instruments Company
-//
-// SPDX-License-Identifier: LGPL-3.0-or-later
-//
-
-module ip_hdr_checksum_tb();
-   
-   initial $dumpfile("ip_hdr_checksum_tb.vcd");
-   initial $dumpvars(0,ip_hdr_checksum_tb);
-
-   reg clk;
-   
-   wire [159:0] in = {
-		      16'h4500,
-		      16'h0030,
-		      16'h4422,
-		      16'h4000,
-		      16'h8006,
-		      16'h0000,
-		      16'h8c7c,
-		      16'h19ac,
-		      16'hae24,
-		      16'h1e2b
-		      };
-   
-   wire [15:0] 	out;
-   ip_hdr_checksum ip_hdr_checksum
-     (.clk(clk), 
-      .in(in),
-      .out(out));
-
-   initial
-     begin
-	clk <= 0;
-	#100 clk <= 1;
-	#100 clk <= 0;
-	#100 clk <= 1;
-	#100 $display("Computed 0x%x, should be 0x442e", out);
-	#100 $finish;
-     end
-   
-endmodule // ip_hdr_checksum_tb