3 // USRP - Universal Software Radio Peripheral
5 // Copyright (C) 2003 Matt Ettus
7 // This program is free software; you can redistribute it and/or modify
8 // it under the terms of the GNU General Public License as published by
9 // the Free Software Foundation; either version 2 of the License, or
10 // (at your option) any later version.
12 // This program is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 51 Franklin Street, Boston, MA 02110-1301 USA
23 // NOTE This only works for N=4, max interp rate of 128
24 // NOTE signal "rate" is ONE LESS THAN the actual rate
26 module cic_int_shifter(rate,signal_in,signal_out);
28 parameter maxbitgain = 21;
31 input wire [bw+maxbitgain-1:0] signal_in;
32 output reg [bw-1:0] signal_out;
34 function [4:0] bitgain;
43 8'd128 : bitgain = 21;
45 // Nearest without overflow
49 8'd9,8'd10 : bitgain = 10;
50 8'd11,8'd12 : bitgain = 11;
51 8'd13,8'd14,8'd15 : bitgain = 12;
52 8'd17,8'd18,8'd19,8'd20 : bitgain = 13;
53 8'd21,8'd22,8'd23,8'd24,8'd25 : bitgain = 14;
54 8'd26,8'd27,8'd28,8'd29,8'd30,8'd31 : bitgain = 15;
55 8'd33,8'd34,8'd35,8'd36,8'd37,8'd38,8'd39,8'd40 : bitgain = 16;
56 8'd41,8'd42,8'd43,8'd44,8'd45,8'd46,8'd47,8'd48,8'd49,8'd50 : bitgain = 17;
57 8'd51,8'd52,8'd53,8'd54,8'd55,8'd56,8'd57,8'd58,8'd59,8'd60,8'd61,8'd62,8'd63 : bitgain = 18;
58 8'd65,8'd66,8'd67,8'd68,8'd69,8'd70,8'd71,8'd72,8'd73,8'd74,8'd75,8'd76,8'd77,8'd78,8'd79,8'd80 : bitgain = 19;
59 8'd81,8'd82,8'd83,8'd84,8'd85,8'd86,8'd87,8'd88,8'd89,8'd90,8'd91,8'd92,8'd93,8'd94,8'd95,8'd96,8'd97,8'd98,8'd99,8'd100,8'd101 : bitgain = 20;
61 default : bitgain = 21;
63 endfunction // bitgain
65 wire [4:0] shift = bitgain(rate+1);
67 // We should be able to do this, but can't ....
68 // assign signal_out = signal_in[shift+bw-1:shift];
72 5'd6 : signal_out = signal_in[6+bw-1:6];
73 5'd9 : signal_out = signal_in[9+bw-1:9];
74 5'd12 : signal_out = signal_in[12+bw-1:12];
75 5'd15 : signal_out = signal_in[15+bw-1:15];
76 5'd18 : signal_out = signal_in[18+bw-1:18];
77 5'd21 : signal_out = signal_in[21+bw-1:21];
79 5'd7 : signal_out = signal_in[7+bw-1:7];
80 5'd8 : signal_out = signal_in[8+bw-1:8];
81 5'd10 : signal_out = signal_in[10+bw-1:10];
82 5'd11 : signal_out = signal_in[11+bw-1:11];
83 5'd13 : signal_out = signal_in[13+bw-1:13];
84 5'd14 : signal_out = signal_in[14+bw-1:14];
85 5'd16 : signal_out = signal_in[16+bw-1:16];
86 5'd17 : signal_out = signal_in[17+bw-1:17];
87 5'd19 : signal_out = signal_in[19+bw-1:19];
88 5'd20 : signal_out = signal_in[20+bw-1:20];
90 default : signal_out = signal_in[21+bw-1:21];
91 endcase // case(shift)
93 endmodule // cic_int_shifter