Verilog if 语句不一致

如何解决Verilog if 语句不一致

我正在尝试使用推送/弹出信号编写一个深度为 8 的简单 4 位堆栈，但它的行为方式非常奇怪。我的一个 if 语句工作正常，而另一个根本无法运行。这是我的代码：

module Stack_8x4(
    input wire clk,input wire reset,input wire push,input wire pop,input wire [3:0] data_in,output reg [3:0] data_out,output reg empty,output reg full
    );
    
    reg [3:0] index;
    reg [3:0] stack [7:0];
    
    always @(posedge reset) begin
        index <= -1;
        data_out = 4'd0;
        empty = 1;
        full = 0;
    end
    always @(posedge clk) begin
        if (push & !pop) begin
            empty = 0;
            if(!full) begin
                index = index + 1;
                stack[index] = data_in;
                if(index > 6) full = 1;
            end
        end
        if (pop & !push) begin
            full = 0;
            if(!empty) begin
                data_out = stack[index];
                index = index - 1;
                if(index < 0) empty= 1;
            end else data_out = 0;
        end
    end
endmodule

如您所见，push 和 pop 的逻辑几乎相同。我的问题是为什么 if(index < 0) empty= 1; 行不起作用而 if(index > 6) full = 1; 工作正常？

以下是测试台和模拟以了解更多详情：

module sim();

reg clk;
reg reset;
reg push;
reg pop;
reg [3:0] data_in;
wire [3:0] data_out;
wire full;
wire empty;
//wire [3:0]i;

always begin
clk = 0;
#5
clk = 1;
#5
clk = 0;
end

initial begin
// setup
reset = 1;
push = 0;
pop = 0;
data_in = 0;
#10
reset = 0;

// idle
#20

// push 1,2,3,4,5,6,7,8,9 to fill the module and test for idling at full
push = 1;
data_in = 1;
#10
data_in = 2;
#10
data_in = 3;
#10
data_in = 4;
#10
data_in = 5;
#10
data_in = 6;
#10
data_in = 7;
#10
data_in = 8;
#10
data_in = 9;
#10
data_in = 10;
#10
data_in = 11;
#10
pop = 1;
#10
push = 0;
#30
pop = 0;
push = 1;
#30
push = 0;
#20
pop = 1;
// pop
//pop = 1;

end

Stack_8x4 S (
    .clk(clk),.push(push),.pop(pop),.reset(reset),.data_in(data_in),.data_out(data_out),.full(full),.empty(empty)
);

endmodule

解决方法

您的主要问题是尝试使用带有无符号变量的有符号数据。因此， index <= -1;、index < 0 不会按您预期的那样工作。我的建议是忘记有符号算术，只做无符号运算。

其他问题：

1. 您应该只使用一个 always 块来执行重置和非重置工作。
2. 你应该在你的always @posedge块中到处使用非阻塞赋值
3. 出于某种原因，由于“索引

所以，这是我重新编写的代码：

   always @(posedge clk) begin
      if (reset) begin
         index <= 0;
         data_out <= 4'd0;
         empty <= 1;
         full <= 0;
      end      
      else if (push & !pop) begin
          if(index < 8) begin
            full<= 0;
            stack[index] <= data_in;
            index <= index + 1;
         end
         else 
           full <= 1;
      end
      else if (pop & !push) begin
         if(index == 0) begin
            empty <= 1;
            data_out <= 0;
         end
         else begin
            empty <= 0;
            index <= index - 1;
            data_out <= stack[index];
         end
      end // if (pop & !push)
   end // always @ (posedge clk)