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Synthesizing taking too long, and I would like help to make it not take so long.

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zpeterson44

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`timescale 1ns / 1ns
module RC4Test
(
input wire clk,
input wire rst,
input wire password_ready,
input wire [55:0] inkey,
output reg output_ready,
output reg [7:0] K
);
 
 
typedef enum bit [3:0] {IDLE,KEYREAD,KEYSCHED1,KEYSCHED2,KEYSCHED3,KEYSCHED4,CRYPTO1,CRYPTO2,CRYPTOPREP} stateType;
 
stateType state;
stateType nxt_state;
 
 
//`define `KEYSIZE 7
// Key
//reg [7:0] key[0:6];
reg [7:0] key[0:6];
// S array
reg [7:0] S[0:256];
reg [9:0] discardCount;
reg [7:0] i;
reg [7:0] j;
reg [7:0] nxt_j;
reg [7:0] tmp;
always_ff @ (posedge clk, negedge rst) begin
    /*$display("i :%d",i);
    $display("State :%s",state);
    $display("password_input :%08b",password_input);*/
    if(1'b0 == rst) begin
        state <= IDLE;
        j <= 0;
    end else begin
        state <= nxt_state;
        j <= nxt_j;
    end
end
 
always_comb begin
    nxt_state = state;
    case(state)
        IDLE: begin
            if(password_ready == 1'b1) begin
                nxt_state = KEYREAD;
            end else begin
                nxt_state = IDLE;
            end
        end
        KEYREAD: begin
            if(i == 8'b00000001) begin
                nxt_state = KEYSCHED1;
            end else begin
                nxt_state = KEYREAD;
            end
        end
        KEYSCHED1: begin
            if(i == 8'b00000000) begin
                nxt_state = KEYSCHED3;
            end else begin
                nxt_state = KEYSCHED1;
            end
        end
        KEYSCHED2: begin
            nxt_state = CRYPTOPREP;
        end
        KEYSCHED3: begin
            if(i == 8'b11111111) begin
                nxt_state = KEYSCHED2;
            end else begin
                if (j != nxt_j) begin
                    nxt_state = KEYSCHED3;
                end else begin
                    nxt_state = KEYSCHED4;
                end
            end
        end
        KEYSCHED4: begin
            if(i == 8'b11111111) begin
                nxt_state = KEYSCHED2;
            end else begin
                if (j != nxt_j) begin
                    nxt_state = KEYSCHED4;
                end else begin
                    nxt_state = KEYSCHED3;
                end
            end
        end
        CRYPTOPREP: begin
            nxt_state = CRYPTO1;
        end
        CRYPTO1: begin
            if (j != nxt_j) begin
                nxt_state = CRYPTO1;
            end else begin
                nxt_state = CRYPTO2;
            end
        end
        CRYPTO2: begin
            if (j != nxt_j) begin
                nxt_state = CRYPTO2;
            end else begin
                nxt_state = CRYPTO1;
            end
        end
        default: begin
        end
    endcase
end
 
always_comb begin
    output_ready = 0;
    K = 8'b00000000;
    //$display ("ALWAYS COMB 2");
    case(state)
        IDLE: begin
            output_ready = 0;
            nxt_j = 0;
            i = 8'b00000000;
        end
        KEYREAD: begin
          
            key[0] = inkey[7:0];
            key[1] = inkey[15:8];
            key[2] = inkey[23:16];
            key[3] = inkey[31:24];
            key[4] = inkey[39:32];
            key[5] = inkey[47:40];
            key[6] = inkey[55:48];
            /*while (i < 8'b00000111) begin
                //$display("%b",key[i]);
                key[i] = inkey[(i*8)+7:(i*8)];
                i = i+1;
            end*/
            i = 8'b00000001;
            /*while (i < 8'b00000111) begin
                key[i] = password_input;
                $display("%b",key[i]);
                i = i+1;
            end
            key[0] = 8'b01011010;
            key[1] = 8'b01100001;
            key[2] = 8'b01100011;
            key[3] = 8'b01101000;
            key[4] = 8'b01100001;
            key[5] = 8'b01110010;
            key[6] = 8'b01111001;*/
            //key[i] = password_input;
                    //$display ("rc4: key[%d] = %08X",i,password_input);
        end
        KEYSCHED1: begin
            while (i < 8'b11111111) begin
                S[i] = i;
                i = i+1;
            end
            S[i] = i;
            S[0] = 0;
 
            i = 8'b00000000;
            nxt_j = (0 + S[i] + key[i % 8'b00000111])%8'b11111111;
            //$display ("nxt_j: %b",nxt_j);
        end
        KEYSCHED2: begin
            //j = (j + S[i] + key[i % 8'b00000111])%8'b11111111;
        ///nxt_j = (nxt_j + S[i] + key[i % 8'b00000111])%8'b11111111;
            S[i] = S[j];
            S[j] = S[i];
            i = 8'b00000001;
            nxt_j = S[1];
            discardCount = 10'b0000000000;
            output_ready = 0;
        end
        KEYSCHED3: begin
            if (i == 8'b11111111) begin
                nxt_j = (nxt_j + S[i] + key[i % 8'b00000111])%8'b11111111;
                S[i] = S[j];
                S[j] = S[i];
            end else begin
                //while (i < 8'b11111111) begin
                    S[i] = S[j];
                        S[j] = S[i];
                    nxt_j = (nxt_j + S[i+1] + key[(i+1) % 8'b00000111])%8'b11111111;
                    i = i + 1;
                    //$display ("j: %b",j);
                    //$display ("nxt_j: %b",nxt_j);
                //end
            end
  
        end
        KEYSCHED4: begin
            if (i == 8'b11111111) begin
                nxt_j = (nxt_j + S[i] + key[i % 8'b00000111])%8'b11111111;
                S[i] = S[j];
                S[j] = S[i];
            end else begin
                //while (i < 8'b11111111) begin
                    S[i] = S[j];
                        S[j] = S[i];
                    nxt_j = (nxt_j + S[i+1] + key[(i+1) % 8'b00000111])%8'b11111111;
                    i = i + 1;
                    //$display ("j: %b",j);
                    //$display ("nxt_j: %b",nxt_j);
                //end
            end
  
        end
        CRYPTOPREP: begin
 
            /*i = 8'b00000000;
            while (i < 8'b11111111) begin
                $display ("S[%d]: %b",i,S[i]);
                i = i+1;
            end
            $display ("S[%d]: %b",i,S[i]);
            i = 8'b00000001;*/
        end
        CRYPTO1: begin
            S[i] = S[j];
            S[j] = S[i];
            tmp = S[i]+S[j];
            output_ready = 0;
            K = S[tmp%8'b11111111];//S[ S[i]+S[j] ];
            if (discardCount<10'b1100000000) begin // discard first 1536 values - SSH RC4 compliant
                discardCount = discardCount + 1;
            end else begin
                output_ready = 1; // Valid K at output
            end
                i = (i+1)%8'b11111111;
                // Here is the secret of 1-clock: we develop all possible values of j in the future
            if (nxt_j==i+1) begin
                nxt_j = (nxt_j + S[i])%8'b11111111;
            end else begin
                if (i==255) begin
                    nxt_j = (nxt_j + S[0])%8'b11111111;
                end else begin
                    nxt_j = (nxt_j + S[i+1])%8'b11111111;
                end
            end
            /*if(output_ready == 1) begin
                $display ("K[%d]: %b",i,K);
            end*/
        end
        CRYPTO2: begin
            S[i] = S[j];
            S[j] = S[i];
            tmp = S[i]+S[j];
            output_ready = 0;
            K = S[tmp%8'b11111111];//S[ S[i]+S[j] ];
                if (discardCount<10'b1100000000) begin // discard first 1536 values - SSH RC4 compliant
                    discardCount = discardCount + 1;
                end else begin
                output_ready = 1; // Valid K at output
            end
                i = (i+1)%8'b11111111;
                // Here is the secret of 1-clock: we develop all possible values of j in the future
                if (nxt_j==i+1) begin
                    nxt_j = (nxt_j + S[i])%8'b11111111;
                end else begin
                    if (i==255) begin
                    nxt_j = (nxt_j + S[0])%8'b11111111;
                        end else begin
                    nxt_j = (nxt_j + S[i+1])%8'b11111111;
                end
            end
            /*if(output_ready == 1) begin
                $display ("K[%d]: %b",i,K);
            end*/
        end
        default: begin
        end
    endcase
end
endmodule
 
Last edited by a moderator:

1) Get a faster computer
2) Get a faster synthesis tool
3) Tell us what you are using, how 'slow' it is, and maybe some more information so MAYBE we'll have SOME idea of what you're doing, rather than just slapping up a bunch code and complaining that it synthesizes too slowly.
 

You do know you don't have to use 'b all the time, there are 'o, 'h, and 'd for octal, hexadecimal, and decimal respectively.

I suspect it's taking so long because of you're indexing into this reg [7:0] S[0:256]; array in the FSM. You wrote the FSM in SystemVerilog just like a direct translation of a software program. In this case you are generating very large logic to deal with the array, probably giant 256-to-1 multiplexers and 1-to-256 decoders all over the place. So yes it will synthesis slowly, it takes a lot of effort to synthesize code like this. Rewrite it as a hardware design with a proper pipeline architecture using memories and I'm sure you'll find it will synthesize quickly.

Also you are using the modulo operator %, which I also think you don't quite understand correctly.
For instance you have..
Code: 
key[i % 8'b00000111]
which is i % 7 and that can't be synthesized as it requires an actual division operation to compute (i.e. non-power of 2). This performs the following:
i=0: 0
i=1: 1
i=2: 2
...
i=6: 6
i=7: 0
i=8: 1
... you get the idea, it only cycles over 7 values not 8.
I suspect you are trying to do a modulo 8 operation here i.e find a remainder from 0-7.
 

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