// // Copyright 2011 Ettus Research LLC // // 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 3 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, see . // // 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