1 files changed, 85 insertions, 0 deletions
diff --git a/fpga/usrp2/sdr_lib/small_hb_int.v b/fpga/usrp2/sdr_lib/small_hb_int.v
new file mode 100644
index 000000000..f80d3cac3
--- /dev/null
+++ b/fpga/usrp2/sdr_lib/small_hb_int.v
@@ -0,0 +1,85 @@
+// 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_int
+  #(parameter WIDTH=18)
+    (input clk,
+     input rst,
+     input bypass,
+     input stb_in,
+     input [WIDTH-1:0] data_in,
+     input [7:0] output_rate,
+     input stb_out,
+     output reg [WIDTH-1:0] data_out);
+
+   reg 		   phase;
+   reg [WIDTH-1:0] d1, d2, d3, d4, d5, d6;
+
+   localparam 	   MWIDTH = 36;
+   wire [MWIDTH-1:0] prod;
+
+   reg [6:0] 	     stbin_d;
+   
+   always @(posedge clk)
+     stbin_d <= {stbin_d[5:0],stb_in};
+   
+   always @(posedge clk)
+     if(stb_in)
+       begin
+	  d1 <= data_in;
+	  d2 <= d1;
+	  d3 <= d2;
+	  d4 <= d3;
+	  d5 <= d4;
+	  d6 <= d5;
+       end
+
+   wire [WIDTH-1:0] sum_outer, sum_inner;
+   add2_and_round_reg #(.WIDTH(WIDTH)) add_outer (.clk(clk),.in1(d1),.in2(d4),.sum(sum_outer));
+   add2_and_round_reg #(.WIDTH(WIDTH)) add_inner (.clk(clk),.in1(d2),.in2(d3),.sum(sum_inner));
+
+   wire [17:0] 	   coeff_outer = -10690;
+   wire [17:0] 	   coeff_inner = 75809;
+
+   MULT18X18S mult(.C(clk), .CE(1), .R(rst), .P(prod), .A(stbin_d[1] ? coeff_outer : coeff_inner), 
+		   .B(stbin_d[1] ? sum_outer : sum_inner) );
+
+   wire [MWIDTH:0] accum;
+   acc #(.IWIDTH(MWIDTH),.OWIDTH(MWIDTH+1)) 
+     acc (.clk(clk),.clear(stbin_d[2]),.acc(|stbin_d[3:2]),.in(prod),.out(accum));
+   
+   wire [WIDTH+2:0] 	 accum_rnd;
+   round_reg #(.bits_in(MWIDTH+1),.bits_out(WIDTH+3))
+     final_round (.clk(clk),.in(accum),.out(accum_rnd));
+
+   wire [WIDTH-1:0] 	 clipped;
+   clip_reg #(.bits_in(WIDTH+3),.bits_out(WIDTH))
+     final_clip (.clk(clk),.in(accum_rnd),.out(clipped));
+
+   reg [WIDTH-1:0] 	 saved, saved_d3;
+   always @(posedge clk)
+     if(stbin_d[6])
+       saved <= clipped;
+
+   always @(posedge clk)
+     if(stbin_d[3])
+       saved_d3 <= d3;
+	   
+   always @(posedge clk)
+     if(bypass)
+       data_out <= data_in;
+     else if(stb_in & stb_out)
+       case(output_rate)
+	 1 : data_out <= d6; 
+	 2 : data_out <= d4;
+	 3, 4, 5, 6, 7 : data_out <= d3;
+	 default : data_out <= d2;
+       endcase // case(output_rate)
+     else if(stb_out)
+       data_out <= saved;
+
+endmodule // small_hb_int
+