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// First halfband iterpolator
// 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 4th clock cycle,
// Strobe out 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_interp
#(parameter IWIDTH=18, OWIDTH=18, ACCWIDTH=24)
(input clk,
input rst,
input bypass,
input [7:0] cpo, // Clocks per output, must be at least 2
input stb_in,
input [IWIDTH-1:0] data_in,
input stb_out,
output reg [OWIDTH-1:0] data_out);
localparam MWIDTH = ACCWIDTH-2;
localparam CWIDTH = 18;
reg [CWIDTH-1:0] coeff1, coeff2;
reg [3:0] addr_a, addr_b, addr_c, addr_d, addr_e;
wire [IWIDTH-1:0] data_a, data_b, data_c, data_d, data_e, sum1, sum2;
wire [35:0] prod1, prod2;
reg [2:0] phase, phase_d1, phase_d2, phase_d3, phase_d4, phase_d5;
always @(posedge clk)
if(rst)
phase <= 0;
else
if(stb_in)
phase <= 1;
else if(phase==4)
phase <= 0;
else if(phase!=0)
phase <= phase + 1;
always @(posedge clk) phase_d1 <= phase;
always @(posedge clk) phase_d2 <= phase_d1;
always @(posedge clk) phase_d3 <= phase_d2;
always @(posedge clk) phase_d4 <= phase_d3;
always @(posedge clk) phase_d5 <= phase_d4;
srl #(.WIDTH(IWIDTH)) srl_a
(.clk(clk),.write(stb_in),.in(data_in),.addr(addr_a),.out(data_a));
srl #(.WIDTH(IWIDTH)) srl_b
(.clk(clk),.write(stb_in),.in(data_in),.addr(addr_b),.out(data_b));
srl #(.WIDTH(IWIDTH)) srl_c
(.clk(clk),.write(stb_in),.in(data_in),.addr(addr_c),.out(data_c));
srl #(.WIDTH(IWIDTH)) srl_d
(.clk(clk),.write(stb_in),.in(data_in),.addr(addr_d),.out(data_d));
srl #(.WIDTH(IWIDTH)) srl_e
(.clk(clk),.write(stb_in),.in(data_in),.addr(addr_e),.out(data_e));
always @*
case(phase)
1 : begin addr_a = 0; addr_b = 15; end
2 : begin addr_a = 1; addr_b = 14; end
3 : begin addr_a = 2; addr_b = 13; end
4 : begin addr_a = 3; addr_b = 12; end
default : begin addr_a = 0; addr_b = 15; end
endcase // case(phase)
always @*
case(phase)
1 : begin addr_c = 4; addr_d = 11; end
2 : begin addr_c = 5; addr_d = 10; end
3 : begin addr_c = 6; addr_d = 9; end
4 : begin addr_c = 7; addr_d = 8; end
default : begin addr_c = 4; addr_d = 11; end
endcase // case(phase)
always @*
case(cpo)
2 : addr_e <= 9;
3,4,5,6,7,8 : addr_e <= 8;
default : addr_e <= 7; // This case works for 256, which = 0 due to overflow outside this block
endcase // case(cpo)
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)
add2_reg /*_and_round_reg*/ #(.WIDTH(IWIDTH)) add1 (.clk(clk),.in1(data_a),.in2(data_b),.sum(sum1));
add2_reg /*_and_round_reg*/ #(.WIDTH(IWIDTH)) add2 (.clk(clk),.in1(data_c),.in2(data_d),.sum(sum2));
// sum1, sum2 available on phase_d1
wire do_mult = 1;
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) );
// prod1, prod2 available on phase_d2
wire [MWIDTH-1:0] sum_of_prod;
add2_and_round_reg #(.WIDTH(MWIDTH))
add3 (.clk(clk),.in1(prod1[35:36-MWIDTH]),.in2(prod2[35:36-MWIDTH]),.sum(sum_of_prod));
// sum_of_prod available on phase_d3
wire [ACCWIDTH-1:0] acc_out;
wire [OWIDTH-1:0] acc_round;
wire clear = (phase_d3 == 1);
wire do_acc = (phase_d3 != 0);
acc #(.IWIDTH(MWIDTH),.OWIDTH(ACCWIDTH))
acc (.clk(clk),.clear(clear),.acc(do_acc),.in(sum_of_prod),.out(acc_out));
// acc_out available on phase_d4
wire [ACCWIDTH-6:0] clipped_acc;
clip #(.bits_in(ACCWIDTH),.bits_out(ACCWIDTH-5)) final_clip(.in(acc_out),.out(clipped_acc));
reg [ACCWIDTH-6:0] clipped_reg;
always @(posedge clk)
if(phase_d4 == 4)
clipped_reg <= clipped_acc;
// clipped_reg available on phase_d5
wire [OWIDTH-1:0] data_out_round;
round #(.bits_in(ACCWIDTH-5),.bits_out(OWIDTH)) final_round (.in(clipped_reg),.out(data_out_round));
reg odd;
always @(posedge clk)
if(rst)
odd <= 0;
else if(stb_in)
odd <= 0;
else if(stb_out)
odd <= 1;
always @(posedge clk)
if(bypass)
data_out <= data_in;
else if(stb_out)
if(odd)
data_out <= data_e;
else
data_out <= data_out_round;
// data_out available on phase_d6
endmodule // hb_interp
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