Merged r5463:5504 from jcorgan/snd into trunk. Work in progress, adds digital loopbac...

[debian/gnuradio] / gr-sounder / src / fpga / lib / sounder_rx.v

diff --git a/gr-sounder/src/fpga/lib/sounder_rx.v b/gr-sounder/src/fpga/lib/sounder_rx.v
index b7c5f48782af8b064bd3f3692ab94350090ae583..338afd55e57f4b24c4f7edbc4275a8ae2e585b18 100644 (file)
--- a/gr-sounder/src/fpga/lib/sounder_rx.v
+++ b/gr-sounder/src/fpga/lib/sounder_rx.v
@@ -19,8 +19,9 @@
 //  Foundation, Inc., 51 Franklin Street, Boston, MA  02110-1301  USA
 //
 
-module sounder_rx(clk_i,rst_i,ena_i,rx_strobe_i,tx_strobe_i,mask_i,len_i,
-                 rx_in_i_i,rx_in_q_i,rx_i_o,rx_q_o,rx_strobe_o);
+module sounder_rx(clk_i,rst_i,ena_i,rx_strobe_i,tx_strobe_i,mask_i,degree_i,len_i,
+                 rx_in_i_i,rx_in_q_i,rx_i_o,rx_q_o,rx_strobe_o,
+                 loop_i);
    
    input         clk_i;                // Master clock
    input         rst_i;         // Subsystem reset
@@ -29,6 +30,7 @@ module sounder_rx(clk_i,rst_i,ena_i,rx_strobe_i,tx_strobe_i,mask_i,len_i,
    input         tx_strobe_i;  // Strobe every transmitted sample
     
    input  [15:0] mask_i;       // PN code LFSR mask
+   input  [4:0]  degree_i;     // PN code LFSR sequency degree
    input  [15:0] len_i;                // PN code LFSR sequence length
    input  [15:0] rx_in_i_i;    // I channel on receive
    input  [15:0] rx_in_q_i;    // Q channel on receive
@@ -37,48 +39,57 @@ module sounder_rx(clk_i,rst_i,ena_i,rx_strobe_i,tx_strobe_i,mask_i,len_i,
    output [15:0] rx_q_o;       // Q channel of impulse response
    output        rx_strobe_o;   // Impulse response value ready
 
-   // LFSR phase counter
-   reg [15:0] count;
-   wire cycle = (count == (len_i - 1));
+   input         loop_i;        // Implement loopback
+   
+   wire strobe_in  = loop_i ? tx_strobe_i : rx_strobe_i;
+   wire [16:0] len = loop_i ? (len_i - 1) : ((len_i << 1) - 2);
+                
+   strobe #(17) phase_strobe(.clk_i(clk_i),.rst_i(rst_i),.ena_i(ena_i),
+                      .rate_i(len),.strobe_i(strobe_in),.strobe_o(rx_strobe_o),
+                      .count_o());
 
-   always @(posedge clk_i)
-     if (rst_i | ~ena_i)
-       count <= 16'b0;
-     else
-       if (cycle)
-        count <= 16'b0;
-       else
-        count <= count + 16'b1;
-           
-   // Retard LFSR phase once per cycle
-   wire lfsr_strobe = (tx_strobe_i & ~cycle);
+   wire pn_ref;
+   wire ref_strobe = tx_strobe_i & ~rx_strobe_o; // Retard reference phase once per period
+   lfsr ref_code
+     ( .clk_i(clk_i),.rst_i(rst_i),.ena_i(ena_i),.strobe_i(ref_strobe),.mask_i(mask_i),.pn_o(pn_ref) );
 
-   // Recreate local reference of transmitted PN code
-   wire pn;
-   lfsr reference
-     ( .clk_i(clk_i),.rst_i(rst_i),.ena_i(ena_i),.strobe_i(lfsr_strobe),.mask_i(mask_i),.pn_o(pn) );
+   wire [5:0] offset = (5'd16-degree_i);
+   
+   reg  [31:0] sum_i, sum_q;
+   reg  [31:0] total_i, total_q;
+   wire [31:0] scaled_i = total_i << offset;
+   wire [31:0] scaled_q = total_q << offset;
+   wire [31:0] i_ext, q_ext;
 
-   wire [31:0] rx_i_ext, rx_q_ext;
-   sign_extend #(16,32) i_extend(rx_in_i_i, rx_i_ext);
-   sign_extend #(16,32) q_extend(rx_in_q_i, rx_q_ext);
+   sign_extend #(16,32) i_extender(rx_in_i_i, i_ext);
+   sign_extend #(16,32) q_extender(rx_in_q_i, q_ext);
 
-   reg [31:0] accum;
+   wire [31:0] prod_i = pn_ref ? i_ext : -i_ext;
+   wire [31:0] prod_q = pn_ref ? q_ext : -q_ext;
+   
    always @(posedge clk_i)
      if (rst_i | ~ena_i)
-       accum <= 32'b0;
-     else
-       if (rx_strobe_i)
-        if (cycle)
-          accum <= 32'b0;
-        else
-          if (pn)
-            accum <= accum + rx_i_ext;
-          else
-            accum <= accum - rx_i_ext;
+       begin
+         sum_i <= 0;
+         sum_q <= 0;
+         total_i <= 0;
+         total_q <= 0;
+       end
+     else if (rx_strobe_o)
+       begin
+         total_i <= sum_i + prod_i;
+         total_q <= sum_q + prod_q;
+         sum_i <= 0;
+         sum_q <= 0;
+       end
+     else if (strobe_in)
+       begin
+         sum_i = sum_i + prod_i;
+         sum_q = sum_q + prod_q;
+       end
+   
+   assign rx_i_o = scaled_i[31:16];
+   assign rx_q_o = scaled_q[31:16];
    
-   assign rx_i_o = accum[31:16];
-   assign rx_q_o = accum[15:0];
-   assign rx_strobe_o = rx_strobe_i & cycle;
-
 endmodule // sounder_rx