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Diffstat (limited to 'fpga/usrp3/lib/dsp/hb_dec.v')
| -rw-r--r-- | fpga/usrp3/lib/dsp/hb_dec.v | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/fpga/usrp3/lib/dsp/hb_dec.v b/fpga/usrp3/lib/dsp/hb_dec.v new file mode 100644 index 000000000..65c771ca7 --- /dev/null +++ b/fpga/usrp3/lib/dsp/hb_dec.v @@ -0,0 +1,177 @@ +// +// 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 |