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// -*- 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
//
module cic_decim
#(parameter bw = 16, parameter N = 4, parameter log2_of_max_rate = 7)
(input clock,
input reset,
input enable,
input [7:0] rate,
input strobe_in,
input strobe_out,
input [bw-1:0] signal_in,
output reg [bw-1:0] signal_out);
localparam maxbitgain = N * log2_of_max_rate;
wire [bw+maxbitgain-1:0] signal_in_ext;
reg [bw+maxbitgain-1:0] integrator [0:N-1];
reg [bw+maxbitgain-1:0] differentiator [0:N-1];
reg [bw+maxbitgain-1:0] pipeline [0:N-1];
reg [bw+maxbitgain-1:0] sampler;
integer i;
sign_extend #(bw,bw+maxbitgain)
ext_input (.in(signal_in),.out(signal_in_ext));
always @(posedge clock)
if(~enable)
for(i=0;i<N;i=i+1)
integrator[i] <= 0;
else if (strobe_in)
begin
integrator[0] <= integrator[0] + signal_in_ext;
for(i=1;i<N;i=i+1)
integrator[i] <= integrator[i] + integrator[i-1];
end
always @(posedge clock)
if(~enable)
begin
sampler <= 0;
for(i=0;i<N;i=i+1)
begin
pipeline[i] <= 0;
differentiator[i] <= 0;
end
end
else if (strobe_out)
begin
sampler <= integrator[N-1];
differentiator[0] <= sampler;
pipeline[0] <= sampler - differentiator[0];
for(i=1;i<N;i=i+1)
begin
differentiator[i] <= pipeline[i-1];
pipeline[i] <= pipeline[i-1] - differentiator[i];
end
end // if (enable && strobe_out)
wire [bw-1:0] signal_out_unreg;
cic_dec_shifter #(bw)
cic_dec_shifter(rate,pipeline[N-1],signal_out_unreg);
always @(posedge clock)
signal_out <= signal_out_unreg;
endmodule // cic_decim
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