dsp: first cut at sigma-delta rounding

2 files changed, 92 insertions, 0 deletions

diff --git a/usrp2/sdr_lib/round_sd.v b/usrp2/sdr_lib/round_sd.v
new file mode 100644
index 000000000..9c2a69615
--- /dev/null
+++ b/usrp2/sdr_lib/round_sd.v
@@ -0,0 +1,43 @@
+
+
+module round_sd
+  #(parameter WIDTH_IN=18,
+    parameter WIDTH_OUT=16)
+   (input clk, input reset,
+    input [WIDTH_IN-1:0] in, output [WIDTH_OUT-1:0] out);
+
+   localparam SUM_WIDTH = WIDTH_IN+1;
+   localparam ERR_WIDTH = SUM_WIDTH - (WIDTH_OUT + 1) + 1;
+   localparam ACC_WIDTH = ERR_WIDTH + 1;
+   
+   reg [ACC_WIDTH-1:0] 	 acc;
+   wire [SUM_WIDTH-1:0] acc_ext, in_ext;
+
+   sign_extend #(.bits_in(WIDTH_IN),.bits_out(SUM_WIDTH)) ext_in (.in(in), .out(in_ext));
+   sign_extend #(.bits_in(ACC_WIDTH),.bits_out(SUM_WIDTH)) ext_acc (.in(acc), .out(acc_ext));
+   
+   wire [SUM_WIDTH-1:0] sum = in_ext + acc_ext;
+   wire [WIDTH_OUT:0] 	sum_round;
+   wire [ERR_WIDTH-1:0] err;
+   wire [ACC_WIDTH-1:0] err_ext;
+   
+   //round_reg #(.bits_in(SUM_WIDTH),.bits_out(WIDTH_OUT+1))  round_sum (.clk(clk), .in(sum), .out(sum_round));
+   round #(.bits_in(SUM_WIDTH),.bits_out(WIDTH_OUT+1))  round_sum ( .in(sum), .out(sum_round));
+
+   reg [WIDTH_IN-1:0] 	in_del;
+   always @(posedge clk)
+     in_del <= in;
+   
+   assign err = in_del - {sum_round,{SUM_WIDTH-WIDTH_OUT-1{1'b0}}};
+   
+   clip #(.bits_in(WIDTH_OUT+1),.bits_out(WIDTH_OUT)) clip (.in(sum_round), .out(out));
+
+   sign_extend #(.bits_in(ERR_WIDTH),.bits_out(ACC_WIDTH)) ext_err (.in(err), .out(err_ext));
+   
+   always @(posedge clk)
+     if(reset)
+       acc <= 0;
+     else
+       acc <= acc + err_ext;
+   
+endmodule // rx_dcoffset
diff --git a/usrp2/sdr_lib/round_sd_tb.v b/usrp2/sdr_lib/round_sd_tb.v
new file mode 100644
index 000000000..df9f58421
--- /dev/null
+++ b/usrp2/sdr_lib/round_sd_tb.v
@@ -0,0 +1,49 @@
+
+module round_sd_tb();
+   
+   reg clk, rst;
+
+   initial rst = 1;
+   initial #1000 rst = 0;
+   initial clk = 0;
+   always #5 clk = ~clk;
+   
+   initial $dumpfile("round_sd_tb.vcd");
+   initial $dumpvars(0,round_sd_tb);
+
+   localparam WIDTH_IN = 14;
+   localparam WIDTH_OUT = 10;
+   
+   reg [WIDTH_IN-1:0] adc_in, adc_in_del;
+   wire [WIDTH_OUT-1:0] adc_out;
+
+   integer 		factor = 1<<(WIDTH_IN-WIDTH_OUT);
+   
+   always @(posedge clk)
+     if(~rst)
+	begin  
+	   if(adc_in_del[WIDTH_IN-1])
+	     $write("-%d\t",-adc_in_del);
+	   else
+	     $write("%d\t",adc_in_del);
+	   if(adc_out[WIDTH_OUT-1])
+	     $write("-%d\t",-adc_out);
+	   else
+	     $write("%d\t",adc_out);
+	   $write("%f\t",adc_in_del/factor);
+	   $write("%f\n",adc_in_del/factor-adc_out);
+	end	
+   
+   round_sd #(.WIDTH_IN(WIDTH_IN),.WIDTH_OUT(WIDTH_OUT)) 
+   round_sd(.clk(clk),.reset(rst), .in(adc_in),.out(adc_out));
+
+   always @(posedge clk)
+     adc_in <= 4734;
+     //adc_in <= $random % 4739;
+
+   always @(posedge clk)
+     adc_in_del <= adc_in;
+
+   initial #10000 $finish;
+   
+endmodule // longfifo_tb