带有条件语句的 always 块内的 For 循环给出了意外错误 [英] For loop inside an always block with conditional statement giving unexpected error

问题描述

我尝试在 always 块中查看与 for 循环相关的不同帖子，但我的问题看起来有所不同.这是我感兴趣的代码部分:

I have tried looking at different posts related to for loop inside an always block but my problem looks different. Here's the part of my code of interest :

   always@(posedge clk) begin
     for(i=2;i<UP_SPACES+2;i=i+1) begin  //Ram_out
        if(up_addr_d2[3:0]==i) 
        begin
          up_dout_t2     <= ram_out[(i+1)*32-1:i*32];                                                                                                    
        end
     end// for loop
  end

我已将 i 声明为整数.此处编译器给出错误i 不是常量".我不确定是否可以通过这种方式进行编码，并且预计会出现多驱动程序错误，但我不明白这个错误.请投灯.

I have declared i as an integer. Here the compiler gives the error 'i is not a constant'. I was not sure if one can code this way and was expecting a multidriver error but this error i dont understand. Please throw light.

推荐答案

此行不合法:

up_dout_t2     <= ram_out[(i+1)*32-1:i*32];

在部分选择中使用冒号右侧的变量值是非法的.基本上，这是非法的:

It is illegal to have a variable value of the right hand side of the colon in a part-select. Basically, this is illegal:

i[a+3 : a]

相反，你必须说:

i[a+3 -: 4]

其中a+3 是起始索引，-: 表示倒计时，4 是宽度.所以，而不是

where a+3 is the starting index, -: means count down and 4 is the width. So, instead of

i[a : a+3] 

你必须说:

i[a +: 4]

i 的索引方向无关紧要.这些代码行适用于

The direction of the index of i doesn't matter. These lines of code would work for either

reg [big:little] i;

或

reg [little:big] i;

因此，您的代码行应该是:

So, your line of code should be:

up_dout_t2     <= ram_out[(i+1)*32-1 -: 32];

或:

up_dout_t2     <= ram_out[i*32 +: 32];

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