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//
// Copyright 2011-2014 Ettus Research LLC
//
//! The USRP digital down-conversion chain
module ddc_chain
#(
parameter BASE = 0,
parameter DSPNO = 0,
parameter WIDTH = 24
)
(input clk, input rst, input clr,
input set_stb, input [7:0] set_addr, input [31:0] set_data,
// From RX frontend
input [WIDTH-1:0] rx_fe_i,
input [WIDTH-1:0] rx_fe_q,
// To RX control
output [31:0] sample,
input run,
output strobe,
output [31:0] debug
);
localparam cwidth = 25;
localparam zwidth = 24;
wire [31:0] phase_inc;
reg [31:0] phase;
wire [17:0] scale_factor;
wire [cwidth-1:0] i_cordic, q_cordic;
wire [WIDTH-1:0] i_cordic_clip, q_cordic_clip;
wire [WIDTH-1:0] i_cic, q_cic;
wire [WIDTH-1:0] i_hb1, q_hb1;
wire [WIDTH-1:0] i_hb2, q_hb2;
wire strobe_cic, strobe_hb1, strobe_hb2;
wire enable_hb1, enable_hb2;
wire [7:0] cic_decim_rate;
reg [WIDTH-1:0] rx_fe_i_mux, rx_fe_q_mux;
wire realmode;
wire swap_iq;
wire invert_i;
wire invert_q;
setting_reg #(.my_addr(BASE+0)) sr_0
(.clk(clk),.rst(rst),.strobe(set_stb),.addr(set_addr),
.in(set_data),.out(phase_inc),.changed());
setting_reg #(.my_addr(BASE+1), .width(18)) sr_1
(.clk(clk),.rst(rst),.strobe(set_stb),.addr(set_addr),
.in(set_data),.out(scale_factor),.changed());
setting_reg #(.my_addr(BASE+2), .width(10)) sr_2
(.clk(clk),.rst(rst),.strobe(set_stb),.addr(set_addr),
.in(set_data),.out({enable_hb1, enable_hb2, cic_decim_rate}),.changed());
setting_reg #(.my_addr(BASE+3), .width(4)) sr_3
(.clk(clk),.rst(rst),.strobe(set_stb),.addr(set_addr),
.in(set_data),.out({invert_i,inver_q,realmode,swap_iq}),.changed());
// MUX so we can do realmode signals on either input
always @(posedge clk)
if(swap_iq)
begin
rx_fe_i_mux <= invert_i ? ~rx_fe_q + 1 : rx_fe_q;
rx_fe_q_mux <= realmode ? 0 : invert_q ? ~rx_fe_i + 1 : rx_fe_i;
end
else
begin
rx_fe_i_mux <= invert_i ? ~rx_fe_i + 1 : rx_fe_i;
rx_fe_q_mux <= realmode ? 0 : invert_i ? ~rx_fe_q + 1 : rx_fe_q;
end
// NCO
always @(posedge clk)
if(rst)
phase <= 0;
else if(~run)
phase <= 0;
else
phase <= phase + phase_inc;
//sign extension of cordic input
wire [cwidth-1:0] to_cordic_i, to_cordic_q;
sign_extend #(.bits_in(WIDTH), .bits_out(cwidth)) sign_extend_cordic_i (.in(rx_fe_i_mux), .out(to_cordic_i));
sign_extend #(.bits_in(WIDTH), .bits_out(cwidth)) sign_extend_cordic_q (.in(rx_fe_q_mux), .out(to_cordic_q));
// CORDIC 24-bit I/O
cordic_z24 #(.bitwidth(cwidth))
cordic(.clock(clk), .reset(rst), .enable(run),
.xi(to_cordic_i),. yi(to_cordic_q), .zi(phase[31:32-zwidth]),
.xo(i_cordic),.yo(q_cordic),.zo() );
clip_reg #(.bits_in(cwidth), .bits_out(WIDTH)) clip_i
(.clk(clk), .in(i_cordic), .strobe_in(1'b1), .out(i_cordic_clip));
clip_reg #(.bits_in(cwidth), .bits_out(WIDTH)) clip_q
(.clk(clk), .in(q_cordic), .strobe_in(1'b1), .out(q_cordic_clip));
// CIC decimator 24 bit I/O
cic_strober cic_strober(.clock(clk),.reset(rst),.enable(run),.rate(cic_decim_rate),
.strobe_fast(1),.strobe_slow(strobe_cic) );
cic_decim #(.bw(WIDTH))
decim_i (.clock(clk),.reset(rst),.enable(run),
.rate(cic_decim_rate),.strobe_in(1'b1),.strobe_out(strobe_cic),
.signal_in(i_cordic_clip),.signal_out(i_cic));
cic_decim #(.bw(WIDTH))
decim_q (.clock(clk),.reset(rst),.enable(run),
.rate(cic_decim_rate),.strobe_in(1'b1),.strobe_out(strobe_cic),
.signal_in(q_cordic_clip),.signal_out(q_cic));
// First (small) halfband 24 bit I/O
small_hb_dec #(.WIDTH(WIDTH)) small_hb_i
(.clk(clk),.rst(rst),.bypass(~enable_hb1),.run(run),
.stb_in(strobe_cic),.data_in(i_cic),.stb_out(strobe_hb1),.data_out(i_hb1));
small_hb_dec #(.WIDTH(WIDTH)) small_hb_q
(.clk(clk),.rst(rst),.bypass(~enable_hb1),.run(run),
.stb_in(strobe_cic),.data_in(q_cic),.stb_out(),.data_out(q_hb1));
// Second (large) halfband 24 bit I/O
wire [8:0] cpi_hb = enable_hb1 ? {cic_decim_rate,1'b0} : {1'b0,cic_decim_rate};
hb_dec #(.WIDTH(WIDTH)) hb_i
(.clk(clk),.rst(rst),.bypass(~enable_hb2),.run(run),.cpi(cpi_hb),
.stb_in(strobe_hb1),.data_in(i_hb1),.stb_out(strobe_hb2),.data_out(i_hb2));
hb_dec #(.WIDTH(WIDTH)) hb_q
(.clk(clk),.rst(rst),.bypass(~enable_hb2),.run(run),.cpi(cpi_hb),
.stb_in(strobe_hb1),.data_in(q_hb1),.stb_out(),.data_out(q_hb2));
//scalar operation (gain of 6 bits)
wire [35:0] prod_i, prod_q;
MULT18X18S mult_i
(.P(prod_i), .A(i_hb2[WIDTH-1:WIDTH-18]), .B(scale_factor), .C(clk), .CE(strobe_hb2), .R(rst) );
MULT18X18S mult_q
(.P(prod_q), .A(q_hb2[WIDTH-1:WIDTH-18]), .B(scale_factor), .C(clk), .CE(strobe_hb2), .R(rst) );
//pipeline for the multiplier (gain of 10 bits)
reg [WIDTH-1:0] prod_reg_i, prod_reg_q;
reg strobe_mult;
always @(posedge clk) begin
strobe_mult <= strobe_hb2;
prod_reg_i <= prod_i[33:34-WIDTH];
prod_reg_q <= prod_q[33:34-WIDTH];
end
// Round final answer to 16 bits
round_sd #(.WIDTH_IN(WIDTH),.WIDTH_OUT(16)) round_i
(.clk(clk),.reset(rst), .in(prod_reg_i),.strobe_in(strobe_mult), .out(sample[31:16]), .strobe_out(strobe));
round_sd #(.WIDTH_IN(WIDTH),.WIDTH_OUT(16)) round_q
(.clk(clk),.reset(rst), .in(prod_reg_q),.strobe_in(strobe_mult), .out(sample[15:0]), .strobe_out());
assign debug = {enable_hb1, enable_hb2, run, strobe, strobe_cic, strobe_hb1, strobe_hb2};
endmodule // ddc_chain
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