如何检查Verilog中的未知逻辑? [英] How to check unknown logic in Verilog?

问题描述

我正在以 6n+1 或 6n-1 的形式检查数字的素性.我有下面的代码，但它似乎没有生成正确的结果.

I'm checking primality of a number in a form of 6n+1 or 6n-1. I have the below code, but it doesn't seem to be generated correct result.

    module prime(clk, rst, start, A, ready, P);

    input clk, rst, start;
    input [7:0] A;

    output ready, P;

    reg ready, P;

    reg [7:0] divisor;
    reg val;


    always @ (posedge clk or negedge rst) begin
        if (!rst) begin
            P <= 1'bx;
        end
        else if (start) 
        begin
            case (A)
               -1 : P <= 1;
                0 : P <= 1;
                1 : P <= 1;
                2 : P <= 1;
                3 : P <= 1;
                5 : P <= 1;
            endcase

            if (A%2 == 0 && A != 2) begin
                P <= 0;
                ready <= 1;
            end

            else if(A > 6) 
            begin
                for(divisor = 5; divisor <= A/divisor; divisor=divisor+6) begin
                    if (A%divisor == 0 || A%(divisor+2) == 0) begin
                        P <= 0;
                    end
                end 

                   if (P != 0 && P == 1'bx) begin // need to fix
                        P <= 1;
                    end
            end
        end
    end
endmodule

关键是这部分似乎不起作用:

The point is that this part doesn't seem to be working:

if (P != 0 && P == 1'bx)

如何检查变量是否包含未知逻辑，即 x.如上检查

How can I check whether a variable includes unknown logic, meaning x. Checking as the above

P == 1'bx

似乎不起作用.

推荐答案

你应该使用 case equal 运算符 (====)，它测试 4-state 逻辑相等，然后是逻辑相等运算符(==).

You should rather use case equality operator (===), which tests 4-state logical equality, then logical equality operator (==).

对于 == 运算符，结果为 x，如果任一操作数包含 x 或 z>.对于 === 运算符位，x 和 z 包含在比较中.

For the == operator, the result is x, if either operand contains an x or a z. For the === operator bits with x and z are included in the comparison.

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