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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
( clock,reset,enable,rate,strobe_in,strobe_out,signal_in,signal_out);
parameter bw = 16;
parameter N = 4;
parameter log2_of_max_rate = 8;
parameter maxbitgain = N * log2_of_max_rate;
input clock;
input reset;
input enable;
input [7:0] rate;
input strobe_in,strobe_out;
input [bw-1:0] signal_in;
output [bw-1:0] signal_out;
reg [bw-1:0] signal_out;
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(reset)
for(i=0;i<N;i=i+1)
integrator[i] <= #1 0;
else if (enable && strobe_in)
begin
integrator[0] <= #1 integrator[0] + signal_in_ext;
for(i=1;i<N;i=i+1)
integrator[i] <= #1 integrator[i] + integrator[i-1];
end
always @(posedge clock)
if(reset)
begin
sampler <= #1 0;
for(i=0;i<N;i=i+1)
begin
pipeline[i] <= #1 0;
differentiator[i] <= #1 0;
end
end
else if (enable && strobe_out)
begin
sampler <= #1 integrator[N-1];
differentiator[0] <= #1 sampler;
pipeline[0] <= #1 sampler - differentiator[0];
for(i=1;i<N;i=i+1)
begin
differentiator[i] <= #1 pipeline[i-1];
pipeline[i] <= #1 pipeline[i-1] - differentiator[i];
end
end // if (enable && strobe_out)
wire [bw+maxbitgain-1:0] signal_out_unnorm = pipeline[N-1];
// Output Scaling to same width as input
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
wire [2:0] shift = log_ceil(rate);
always @*
case(shift)
3'd2 : signal_out = signal_out_unnorm[2*N+bw-1:2*N]; // Decim by 4
3'd3 : signal_out = signal_out_unnorm[3*N+bw-1:3*N];
3'd4 : signal_out = signal_out_unnorm[4*N+bw-1:4*N];
3'd5 : signal_out = signal_out_unnorm[5*N+bw-1:5*N];
3'd6 : signal_out = signal_out_unnorm[6*N+bw-1:6*N];
3'd7 : signal_out = signal_out_unnorm[7*N+bw-1:7*N];
default : signal_out = signal_out_unnorm[7*N+bw-1:7*N];
endcase // case(shift)
endmodule // cic_decim
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