Imported Upstream version 3.2.2

[debian/gnuradio] / usrp / fpga / sdr_lib / cic_int_shifter.v

diff --git a/usrp/fpga/sdr_lib/cic_int_shifter.v b/usrp/fpga/sdr_lib/cic_int_shifter.v
index fd928373b4fee0ae0ca1a6390db0ceabb382c813..a8a3276f14027d9367b5feb419ba306434a056c1 100644 (file)
--- a/usrp/fpga/sdr_lib/cic_int_shifter.v
+++ b/usrp/fpga/sdr_lib/cic_int_shifter.v
@@ -20,37 +20,34 @@
 //
 
 
+// NOTE   This only works for N=4, max interp rate of 128
+// NOTE   signal "rate" is ONE LESS THAN the actual rate
+
 module cic_int_shifter(rate,signal_in,signal_out);
    parameter bw = 16;
-   parameter N = 4;
-   parameter log2_of_max_rate = 7;
-   parameter maxbitgain = (N-1)*log2_of_max_rate;
+   parameter maxbitgain = 21;
    
    input [7:0] rate;
    input       wire [bw+maxbitgain-1:0] signal_in;
    output      reg [bw-1:0] signal_out;
 
-   function [2:0] log_ceil;
-      input [7:0] val;
-      log_ceil = val[6] ? 3'd7 : val[5] ? 3'd6 : val[4] ? 3'd5 : 
-                val[3] ? 3'd4 : val[2] ? 3'd3 : val[1] ? 3'd2 : 3'd1; 
-   endfunction // log_ceil
-   
    function [4:0] bitgain;
       input [7:0] rate;
       case(rate)
-       8'd4 : bitgain = 2*(N-1);
-       8'd8 : bitgain = 3*(N-1);
-       8'd16 : bitgain = 4*(N-1);
-       8'd32 : bitgain = 5*(N-1);
-       8'd64 : bitgain = 6*(N-1);
-       8'd128 : bitgain = 7*(N-1);
+       // Exact Cases
+       8'd4 : bitgain = 6;
+       8'd8 : bitgain = 9;
+       8'd16 : bitgain = 12;
+       8'd32 : bitgain = 15;
+       8'd64 : bitgain = 18;
+       8'd128 : bitgain = 21;
        
+       // Nearest without overflow
        8'd5 : bitgain = 7;
        8'd6 : bitgain = 8;
        8'd7 : bitgain = 9;
        8'd9,8'd10 : bitgain = 10;
-       8'd12 : bitgain = 11;
+       8'd11,8'd12 : bitgain = 11;
        8'd13,8'd14,8'd15 : bitgain = 12;
        8'd17,8'd18,8'd19,8'd20 : bitgain = 13;
        8'd21,8'd22,8'd23,8'd24,8'd25 : bitgain = 14;
@@ -90,7 +87,6 @@ module cic_int_shifter(rate,signal_in,signal_out);
        5'd19 : signal_out = signal_in[19+bw-1:19];
        5'd20 : signal_out = signal_in[20+bw-1:20];
        
-       
        default : signal_out = signal_in[21+bw-1:21];
      endcase // case(shift)