//
+// 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;
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)