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Finally converging on a decent lfsr module
- Lesson 1: Keep it simple!!! - Lesson 2: Make each program do one thing well. (unix) - Lesson 3: Make module dynamic (parameters and ifdefs are horrible!) - Lesson 4: Synthesis can remove bits set to 0 in design... - Lesson 5: Dynamic binding/programmabiility is better!
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//#############################################################################
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//# Function: Random number generator #
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//#############################################################################
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//# Author: Andreas Olofsson #
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//# License: MIT (see LICENSE file in OH! repository) #
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//#############################################################################
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//
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// References:
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// https://users.ece.cmu.edu/~koopman/lfsr/index.html
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//
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//############################################################################
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module oh_random
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#(parameter N = 32 //support multiple of 32 for now...
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/******************************************************************************
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* Function: Linear Feedback Shift Register (Galois)
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* Author: Andreas Olofsson
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* License: MIT (see LICENSE file in OH! repository)
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*
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* Documentation:
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*
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* - A generic Galois LFSR with taps and seeds feed in externally to enable
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* dynamically programming the taps and seed. Shift is from MSB to LSB,
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* feedback bit is from LSB.
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*
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* - The lsfr updates when enable is set to 1.
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*
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* - Any non-zero seed value is legal.
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*
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* - Driving taps externally is only practical with GALOIS configuration,
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* since the massive xor tree would be prohibitive with FIBONACCI.
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* - Example terms from: https://users.ece.cmu.edu/~koopman/lfsr/index.html
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*
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* N POLYNOMIAL
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* -------------------
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* 4 9
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* 5 12
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* 6 21
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* 7 41
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* 8 8E
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* 9 108
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* 10 204
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* 11 402
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* 12 829
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* 13 100D
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* 14 2015
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* 15 4001
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* 16 8016
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* 17 10004
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* 18 20013
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* 19 40013
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* 20 80004
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* 21 100002
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* 22 200001
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* 23 400010
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* 24 80000D
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* 25 1000004
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* 26 2000023
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* 27 4000013
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* 28 8000004
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* 29 10000002
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* 30 20000029
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* 31 40000004
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* 32 80000057
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* 58 200000000000031
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* 64 800000000000000D
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*
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****************************************************************************/
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module oh_lfsr
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#(parameter N = 32, // length of LFSR
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parameter TYPE = "GALOIS" // lfsr type (only galois supported ...)
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)
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(
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input clk,
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input nreset, //async reset
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input en, // enable counter
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input [1:0] mode,// 0=fibonacci,1=galois
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input lsbfirst,// 1=shift from lsb, 0=shift from msb
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input [N-1:0] taps, // taps
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input [N-1:0] seed, // seed
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input [N-1:0] mask, // mask output (1 = active)
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output [N-1:0] out // output value
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input clk,
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input nreset, //async reset
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input en, // enables (advances) lfsr
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input [N-1:0] taps, // taps
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input [N-1:0] seed, // seed
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output reg [N-1:0] out // output value/state vector
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);
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// TODO: support non-multiples of 32
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reg [N-1:0] lfsr_reg[0:N/32-1];
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wire [N-1:0] lfsr_in[0:N/32-1];
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wire [N-1:0] taps_sel[0:N/32-1];
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wire [N/32-1:0] feedback;
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// instantiate multiple 32bit rngs
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genvar i,j;
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generate
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for(i=0;i<(N/32);i=i+1) begin
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//taps
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assign taps_sel[i] = entaps ? taps[(i+1)*32-1:i*32]: 32'h80000057 << 1;
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//lfsr reg
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always @(posedge clk or negedge nreset)
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if (TYPE == "GALOIS") begin
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always @ (posedge clk or negedge nreset)
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if(~nreset)
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lfsr_reg[i] <= seed[(i+1)*32-1:i*32];
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out[N-1:0] <= seed[N-1:0];
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else if(en)
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lfsr_reg[i] <= lfsr_in[i];
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// feeback
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assign feedback[i] = lfsr_reg[i][31];
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assign lfsr_in[i][0] = feedback[i];
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for(j=1;j<32;j=j+1) begin
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assign lfsr_in[i][j] = taps_sel[i][j] ? (lfsr_reg[i][j-1] ^ feedback[i]) :
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lfsr_reg[i][j-1];
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end
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assign out[(i+1)*32-1:i*32] = mask[(i+1)*32-1:i*32] & lfsr_reg[i];
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end // for (i=0;<N/32;i=i+1)
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out[N-1:0] <= ({(N){out[0]}} & taps[N-1:0]) ^
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(out[N-1:0] >> 1);
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end
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else if (TYPE == "FIBONACCI") begin
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initial
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$display("UNSUPPORTED");
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end
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endgenerate
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endmodule // oh_random
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endmodule // oh_lfsr
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@ -1,53 +0,0 @@
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//#############################################################################
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//# Function: Random number generator #
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//#############################################################################
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//# Author: Andreas Olofsson #
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//# License: MIT (see LICENSE file in OH! repository) #
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//#############################################################################
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module oh_random
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#(parameter N = 32 //support multiple of 32 for now...
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)
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(
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input clk,
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input nreset, //async reset
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input en, // enable counter
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input entaps, // enable taps input
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input [N-1:0] taps, // user driven taps
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input [N-1:0] seed, // seed
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input [N-1:0] mask, // mask output (1 = active)
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output [N-1:0] out //random output pulse
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);
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// TODO: support non-multiples of 32
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reg [N-1:0] lfsr_reg[0:N/32-1];
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wire [N-1:0] lfsr_in[0:N/32-1];
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wire [N-1:0] taps_sel[0:N/32-1];
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wire [N/32-1:0] feedback;
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// instantiate multiple 32bit rngs
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genvar i,j;
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generate
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for(i=0;i<(N/32);i=i+1) begin
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//taps
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assign taps_sel[i] = entaps ? taps[(i+1)*32-1:i*32]: 32'h80000057 << 1;
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//lfsr reg
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always @(posedge clk or negedge nreset)
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if(~nreset)
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lfsr_reg[i] <= seed[(i+1)*32-1:i*32];
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else if(en)
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lfsr_reg[i] <= lfsr_in[i];
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// feeback
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assign feedback[i] = lfsr_reg[i][31];
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assign lfsr_in[i][0] = feedback[i];
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for(j=1;j<32;j=j+1) begin
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assign lfsr_in[i][j] = taps_sel[i][j] ? (lfsr_reg[i][j-1] ^ feedback[i]) :
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lfsr_reg[i][j-1];
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end
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assign out[(i+1)*32-1:i*32] = mask[(i+1)*32-1:i*32] & lfsr_reg[i];
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end // for (i=0;<N/32;i=i+1)
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endgenerate
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endmodule // oh_random
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