1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
// -*- verilog -*-
//
// USRP - Universal Software Radio Peripheral
//
// Copyright (C) 2003 Matt Ettus
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Boston, MA 02110-1301 USA
//
// 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 maxbitgain = 21;
input [7:0] rate;
input wire [bw+maxbitgain-1:0] signal_in;
output reg [bw-1:0] signal_out;
function [4:0] bitgain;
input [7:0] rate;
case(rate)
// 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'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;
8'd26,8'd27,8'd28,8'd29,8'd30,8'd31 : bitgain = 15;
8'd33,8'd34,8'd35,8'd36,8'd37,8'd38,8'd39,8'd40 : bitgain = 16;
8'd41,8'd42,8'd43,8'd44,8'd45,8'd46,8'd47,8'd48,8'd49,8'd50 : bitgain = 17;
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;
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;
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;
default : bitgain = 21;
endcase // case(rate)
endfunction // bitgain
wire [4:0] shift = bitgain(rate+1);
// We should be able to do this, but can't ....
// assign signal_out = signal_in[shift+bw-1:shift];
always @*
case(shift)
5'd6 : signal_out = signal_in[6+bw-1:6];
5'd9 : signal_out = signal_in[9+bw-1:9];
5'd12 : signal_out = signal_in[12+bw-1:12];
5'd15 : signal_out = signal_in[15+bw-1:15];
5'd18 : signal_out = signal_in[18+bw-1:18];
5'd21 : signal_out = signal_in[21+bw-1:21];
5'd7 : signal_out = signal_in[7+bw-1:7];
5'd8 : signal_out = signal_in[8+bw-1:8];
5'd10 : signal_out = signal_in[10+bw-1:10];
5'd11 : signal_out = signal_in[11+bw-1:11];
5'd13 : signal_out = signal_in[13+bw-1:13];
5'd14 : signal_out = signal_in[14+bw-1:14];
5'd16 : signal_out = signal_in[16+bw-1:16];
5'd17 : signal_out = signal_in[17+bw-1:17];
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)
endmodule // cic_int_shifter
|
