1 files changed, 111 insertions, 0 deletions
diff --git a/fpga/usrp2/sdr_lib/small_hb_dec.v b/fpga/usrp2/sdr_lib/small_hb_dec.v
new file mode 100644
index 000000000..8519b628a
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/small_hb_dec.v
@@ -0,0 +1,111 @@
+// Short halfband decimator (intended to be followed by another stage)
+// Implements impulse responses of the form [A 0 B 0.5 B 0 A]
+//
+// These taps designed by halfgen4 from ldoolittle:
+//   2 * 131072 * halfgen4(.75/8,2)
+module small_hb_dec
+  #(parameter WIDTH=18)
+    (input clk,
+     input rst,
+     input bypass,
+     input run,
+     input stb_in,
+     input [WIDTH-1:0] data_in,
+     output reg stb_out,
+     output [WIDTH-1:0] data_out);
+
+   reg 			stb_in_d1;
+   reg [WIDTH-1:0] 	data_in_d1;
+   always @(posedge clk) stb_in_d1 <= stb_in;
+   always @(posedge clk) data_in_d1 <= data_in;
+   
+   wire 		go;
+   reg 			phase, go_d1, go_d2, go_d3, go_d4;
+   always @(posedge clk)
+     if(rst | ~run)
+       phase <= 0;
+     else if(stb_in_d1)
+       phase <= ~phase;
+   assign 		go = stb_in_d1 & phase;
+   always @(posedge clk) 
+     if(rst | ~run)
+       begin
+	  go_d1 <= 0;
+	  go_d2 <= 0;
+	  go_d3 <= 0;
+	  go_d4 <= 0;
+       end
+     else
+       begin
+	  go_d1 <= go;
+	  go_d2 <= go_d1;
+	  go_d3 <= go_d2;
+	  go_d4 <= go_d3;
+       end
+
+   wire [17:0] 		coeff_a = -10690;
+   wire [17:0] 		coeff_b = 75809;
+   
+   reg [WIDTH-1:0] 	d1, d2, d3, d4 , d5, d6;
+   always @(posedge clk)
+     if(stb_in_d1 | rst)
+       begin
+	  d1 <= data_in_d1;
+	  d2 <= d1;
+	  d3 <= d2;
+	  d4 <= d3;
+	  d5 <= d4;
+	  d6 <= d5;
+       end
+
+   reg [17:0] sum_a, sum_b, middle, middle_d1;
+   wire [17:0] sum_a_unreg, sum_b_unreg;
+   add2 #(.WIDTH(18)) add2_a (.in1(data_in_d1),.in2(d6),.sum(sum_a_unreg));
+   add2 #(.WIDTH(18)) add2_b (.in1(d2),.in2(d4),.sum(sum_b_unreg));
+   
+   always @(posedge clk)
+     if(go)
+       begin
+	  sum_a <= sum_a_unreg;
+	  sum_b <= sum_b_unreg;
+	  middle <= d3;
+       end
+
+   always @(posedge clk)
+     if(go_d1)
+       middle_d1 <= middle;
+   
+   wire [17:0] sum = go_d1 ? sum_b : sum_a;
+   wire [17:0] coeff = go_d1 ? coeff_b : coeff_a;
+   wire [35:0] 	 prod;   
+   MULT18X18S mult(.C(clk), .CE(go_d1 | go_d2), .R(rst), .P(prod), .A(coeff), .B(sum) );
+   
+   reg [35:0] 	 accum;
+   always @(posedge clk)
+     if(rst)
+       accum <= 0;
+     else if(go_d2)
+       accum <= {middle_d1[17],middle_d1[17],middle_d1,16'd0} + {prod};
+     else if(go_d3)
+       accum <= accum + {prod};
+   
+   wire [17:0] 	 accum_rnd;
+   round #(.bits_in(36),.bits_out(18)) round_acc (.in(accum),.out(accum_rnd));
+
+   reg [17:0] 	 final_sum;
+   always @(posedge clk)
+     if(bypass)
+       final_sum <= data_in_d1;
+     else if(go_d4)
+       final_sum <= accum_rnd;
+
+   assign 	 data_out = final_sum;
+
+   always @(posedge clk)
+     if(rst)
+       stb_out <= 0;
+     else if(bypass)
+       stb_out <= stb_in_d1;
+     else
+       stb_out <= go_d4;
+endmodule // small_hb_dec