diff options
Diffstat (limited to 'fpga/usrp2/sdr_lib/cic_dec_shifter.v')
| -rw-r--r-- | fpga/usrp2/sdr_lib/cic_dec_shifter.v | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/fpga/usrp2/sdr_lib/cic_dec_shifter.v b/fpga/usrp2/sdr_lib/cic_dec_shifter.v new file mode 100644 index 000000000..aa5ac895b --- /dev/null +++ b/fpga/usrp2/sdr_lib/cic_dec_shifter.v @@ -0,0 +1,106 @@ +// -*- 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 decim rate of 128 +// NOTE signal "rate" is EQUAL TO the actual rate, no more -1 BS + +module cic_dec_shifter(rate,signal_in,signal_out); + parameter bw = 16; + parameter maxbitgain = 28; + + 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 -- N*log2(rate) + 8'd1 : bitgain = 0; + 8'd2 : bitgain = 4; + 8'd4 : bitgain = 8; + 8'd8 : bitgain = 12; + 8'd16 : bitgain = 16; + 8'd32 : bitgain = 20; + 8'd64 : bitgain = 24; + 8'd128 : bitgain = 28; + + // Nearest without overflow -- ceil(N*log2(rate)) + 8'd3 : bitgain = 7; + 8'd5 : bitgain = 10; + 8'd6 : bitgain = 11; + 8'd7 : bitgain = 12; + 8'd9 : bitgain = 13; + 8'd10,8'd11 : bitgain = 14; + 8'd12,8'd13 : bitgain = 15; + 8'd14,8'd15 : bitgain = 16; + 8'd17,8'd18,8'd19 : bitgain = 17; + 8'd20,8'd21,8'd22 : bitgain = 18; + 8'd23,8'd24,8'd25,8'd26 : bitgain = 19; + 8'd27,8'd28,8'd29,8'd30,8'd31 : bitgain = 20; + 8'd33,8'd34,8'd35,8'd36,8'd37,8'd38 : bitgain = 21; + 8'd39,8'd40,8'd41,8'd42,8'd43,8'd44,8'd45 : bitgain = 22; + 8'd46,8'd47,8'd48,8'd49,8'd50,8'd51,8'd52,8'd53 : bitgain = 23; + 8'd54,8'd55,8'd56,8'd57,8'd58,8'd59,8'd60,8'd61,8'd62,8'd63 : bitgain = 24; + 8'd65,8'd66,8'd67,8'd68,8'd69,8'd70,8'd71,8'd72,8'd73,8'd74,8'd75,8'd76 : bitgain = 25; + 8'd77,8'd78,8'd79,8'd80,8'd81,8'd82,8'd83,8'd84,8'd85,8'd86,8'd87,8'd88,8'd89,8'd90 : bitgain = 26; + 8'd91,8'd92,8'd93,8'd94,8'd95,8'd96,8'd97,8'd98,8'd99,8'd100,8'd101,8'd102,8'd103,8'd104,8'd105,8'd106,8'd107 : bitgain = 27; + default : bitgain = 28; + endcase // case(rate) + endfunction // bitgain + + wire [4:0] shift = bitgain(rate); + + // We should be able to do this, but can't .... + // assign signal_out = signal_in[shift+bw-1:shift]; + + always @* + case(shift) + 5'd0 : signal_out = signal_in[0+bw-1:0]; + 5'd4 : signal_out = signal_in[4+bw-1:4]; + 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'd12 : signal_out = signal_in[12+bw-1:12]; + 5'd13 : signal_out = signal_in[13+bw-1:13]; + 5'd14 : signal_out = signal_in[14+bw-1:14]; + 5'd15 : signal_out = signal_in[15+bw-1:15]; + 5'd16 : signal_out = signal_in[16+bw-1:16]; + 5'd17 : signal_out = signal_in[17+bw-1:17]; + 5'd18 : signal_out = signal_in[18+bw-1:18]; + 5'd19 : signal_out = signal_in[19+bw-1:19]; + 5'd20 : signal_out = signal_in[20+bw-1:20]; + 5'd21 : signal_out = signal_in[21+bw-1:21]; + 5'd22 : signal_out = signal_in[22+bw-1:22]; + 5'd23 : signal_out = signal_in[23+bw-1:23]; + 5'd24 : signal_out = signal_in[24+bw-1:24]; + 5'd25 : signal_out = signal_in[25+bw-1:25]; + 5'd26 : signal_out = signal_in[26+bw-1:26]; + 5'd27 : signal_out = signal_in[27+bw-1:27]; + 5'd28 : signal_out = signal_in[28+bw-1:28]; + + default : signal_out = signal_in[28+bw-1:28]; + endcase // case(shift) + +endmodule // cic_dec_shifter + |