//
+// 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)
+ // Exact Cases
8'd4 : bitgain = 2*(N-1);
8'd8 : bitgain = 3*(N-1);
8'd16 : bitgain = 4*(N-1);
8'd64 : bitgain = 6*(N-1);
8'd128 : bitgain = 7*(N-1);
+ // Nearest without overflow
8'd5 : bitgain = 7;
8'd6 : bitgain = 8;
8'd7 : bitgain = 9;
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)