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//
// Copyright 2011 Ettus Research LLC
//
// Final halfband decimator
// Implements impulse responses of the form [A 0 B 0 C .. 0 H 0.5 H 0 .. C 0 B 0 A]
// Strobe in cannot come faster than every 2nd clock cycle
// These taps designed by halfgen4 from ldoolittle
// myfilt = round(2^18 * halfgen4(.7/4,8))
module hb_dec
#(parameter WIDTH=24)
(input clk,
input rst,
input bypass,
input run,
input [8:0] cpi, // Clocks per input -- equal to the decimation ratio ahead of this block
input stb_in,
input [WIDTH-1:0] data_in,
output reg stb_out,
output reg [WIDTH-1:0] data_out);
localparam INTWIDTH = 17;
localparam ACCWIDTH = WIDTH + 3;
// Round off inputs to 17 bits because of 18 bit multipliers
wire [INTWIDTH-1:0] data_rnd;
wire stb_rnd;
round_sd #(.WIDTH_IN(WIDTH),.WIDTH_OUT(INTWIDTH)) round_in
(.clk(clk),.reset(rst),.in(data_in),.strobe_in(stb_in),.out(data_rnd),.strobe_out(stb_rnd));
// Control
reg [3:0] addr_odd_a, addr_odd_b, addr_odd_c, addr_odd_d;
wire write_odd, write_even, do_mult;
reg odd;
reg [2:0] phase, phase_d1;
reg stb_out_int;
wire clear, do_acc;
assign do_mult = 1;
always @(posedge clk)
if(rst | ~run)
odd <= 0;
else if(stb_rnd)
odd <= ~odd;
assign write_odd = stb_rnd & odd;
assign write_even = stb_rnd & ~odd;
always @(posedge clk)
if(rst | ~run)
phase <= 0;
else if(stb_rnd & odd)
phase <= 1;
else if(phase == 4)
phase <= 0;
else if(phase != 0)
phase <= phase + 1;
always @(posedge clk)
phase_d1 <= phase;
reg [15:0] stb_out_pre;
always @(posedge clk)
if(rst)
stb_out_pre <= 0;
else
stb_out_pre <= {stb_out_pre[14:0],(stb_rnd & odd)};
always @*
case(phase)
1 : begin addr_odd_a = 0; addr_odd_b = 15; end
2 : begin addr_odd_a = 1; addr_odd_b = 14; end
3 : begin addr_odd_a = 2; addr_odd_b = 13; end
4 : begin addr_odd_a = 3; addr_odd_b = 12; end
default : begin addr_odd_a = 0; addr_odd_b = 15; end
endcase // case(phase)
always @*
case(phase)
1 : begin addr_odd_c = 4; addr_odd_d = 11; end
2 : begin addr_odd_c = 5; addr_odd_d = 10; end
3 : begin addr_odd_c = 6; addr_odd_d = 9; end
4 : begin addr_odd_c = 7; addr_odd_d = 8; end
default : begin addr_odd_c = 4; addr_odd_d = 11; end
endcase // case(phase)
assign do_acc = |stb_out_pre[6:3];
assign clear = stb_out_pre[3];
// Data
wire [INTWIDTH-1:0] data_odd_a, data_odd_b, data_odd_c, data_odd_d;
reg [INTWIDTH:0] sum1, sum2; // these are 18-bit inputs to mult
reg [WIDTH:0] final_sum;
wire [WIDTH-1:0] final_sum_clip;
reg [17:0] coeff1, coeff2;
wire [35:0] prod1, prod2;
always @* // Outer coeffs
case(phase_d1)
1 : coeff1 = -107;
2 : coeff1 = 445;
3 : coeff1 = -1271;
4 : coeff1 = 2959;
default : coeff1 = -107;
endcase // case(phase)
always @* // Inner coeffs
case(phase_d1)
1 : coeff2 = -6107;
2 : coeff2 = 11953;
3 : coeff2 = -24706;
4 : coeff2 = 82359;
default : coeff2 = -6107;
endcase // case(phase)
srl #(.WIDTH(INTWIDTH)) srl_odd_a
(.clk(clk),.write(write_odd),.in(data_rnd),.addr(addr_odd_a),.out(data_odd_a));
srl #(.WIDTH(INTWIDTH)) srl_odd_b
(.clk(clk),.write(write_odd),.in(data_rnd),.addr(addr_odd_b),.out(data_odd_b));
srl #(.WIDTH(INTWIDTH)) srl_odd_c
(.clk(clk),.write(write_odd),.in(data_rnd),.addr(addr_odd_c),.out(data_odd_c));
srl #(.WIDTH(INTWIDTH)) srl_odd_d
(.clk(clk),.write(write_odd),.in(data_rnd),.addr(addr_odd_d),.out(data_odd_d));
always @(posedge clk) sum1 <= {data_odd_a[INTWIDTH-1],data_odd_a} + {data_odd_b[INTWIDTH-1],data_odd_b};
always @(posedge clk) sum2 <= {data_odd_c[INTWIDTH-1],data_odd_c} + {data_odd_d[INTWIDTH-1],data_odd_d};
wire [INTWIDTH-1:0] data_even;
reg [3:0] addr_even;
always @(posedge clk)
case(cpi)
// 1 is an error
2 : addr_even <= 9; // Maximum speed (overall decim by 4)
3, 4, 5, 6, 7 : addr_even <= 8;
default : addr_even <= 7;
endcase // case(cpi)
srl #(.WIDTH(INTWIDTH)) srl_even
(.clk(clk),.write(write_even),.in(data_rnd),.addr(addr_even),.out(data_even));
MULT18X18S mult1(.C(clk), .CE(do_mult), .R(rst), .P(prod1), .A(coeff1), .B(sum1) );
MULT18X18S mult2(.C(clk), .CE(do_mult), .R(rst), .P(prod2), .A(coeff2), .B(sum2) );
reg [35:0] sum_of_prod;
always @(posedge clk) sum_of_prod <= prod1 + prod2; // Can't overflow
wire [ACCWIDTH-1:0] acc_out;
acc #(.IWIDTH(ACCWIDTH-2),.OWIDTH(ACCWIDTH))
acc (.clk(clk),.clear(clear),.acc(do_acc),.in(sum_of_prod[35:38-ACCWIDTH]),.out(acc_out));
wire [ACCWIDTH-1:0] data_even_signext;
localparam SHIFT_FACTOR = 6;
sign_extend #(.bits_in(INTWIDTH),.bits_out(ACCWIDTH-SHIFT_FACTOR)) signext_data_even
(.in(data_even),.out(data_even_signext[ACCWIDTH-1:SHIFT_FACTOR]));
assign data_even_signext[SHIFT_FACTOR-1:0] = 0;
always @(posedge clk) final_sum <= acc_out + data_even_signext;
clip #(.bits_in(WIDTH+1), .bits_out(WIDTH)) clip (.in(final_sum), .out(final_sum_clip));
// Output MUX to allow for bypass
wire selected_stb = bypass ? stb_in : stb_out_pre[8];
always @(posedge clk)
begin
stb_out <= selected_stb;
if(selected_stb)
data_out <= bypass ? data_in : final_sum_clip;
end
endmodule // hb_dec
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