在 Verilog 中转换线值以进行进一步处理

发布于 2024-12-06 07:19:02 字数 479 浏览 2 评论 0原文

我是 Verilog 新手。

我已经编写了将线值转换为整数的代码：

wire [31:0] w1;
integer k;
always @ (w1) k = w1;

来源：在verilog中将连线值转换为整数

现在，对于下一部分，我收到错误！

wire [63:0] w2; // Suppose it contains some value
wire [63:0] w3;
assign w3[k-1:0] = w2[k-1:0]; // ERROR in this line

ERROR : k is not a constant.

我该如何解决这个问题？

原文

I'm new to Verilog.

I have written code to convert a wire value to an integer:

wire [31:0] w1;
integer k;
always @ (w1) k = w1;

Source: converting a wire value to an integer in verilog

Now, for the next part I get an ERROR!

wire [63:0] w2; // Suppose it contains some value
wire [63:0] w3;
assign w3[k-1:0] = w2[k-1:0]; // ERROR in this line

ERROR : k is not a constant.

How do I solve this issue?

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又爬满兰若 2024-12-13 07:19:02

Verilog 要求部分选择（例如 [msb:lsb] 的代码用于选择向量的一部分）是恒定的。要访问可变大小的位组需要更复杂的东西。这是一种实现方法：

wire [63:0] src;
wire [6:0] k;

wire [127:0] mask = { { 64 { 1'b0 } }, { 64 { 1'b1 } } } << k;

wire [63:0] dest;

assign dest = mask[127:64] & src;

这里的技术是构造一个由 64 个 0 后跟 64 个 1 组成的向量，将该向量移位一个可变量，然后使用该向量的一部分作为限定掩码来控制传输哪些位从src到dest。

一个相关的概念对您的示例没有帮助，但值得注意：Verilog-2001 引入了“索引部分选择”。索引部分选择指定基本索引和宽度。宽度需要恒定，但基本索引不需要恒定。索引部分选择的语法为 vec[base+:width] 或 vec[base-:width]。

Verilog requires that part selects (code like [msb:lsb] to select part of a vector) be constant. To access a variable-sized group of bits requires something more complicated. Here is one way to do it:

wire [63:0] src;
wire [6:0] k;

wire [127:0] mask = { { 64 { 1'b0 } }, { 64 { 1'b1 } } } << k;

wire [63:0] dest;

assign dest = mask[127:64] & src;

The technique here is to construct a vector of 64 zeros followed by 64 ones, shift that vector by a variable amount, and then use a portion of the vector as a qualifying mask to control which bits are transferred from src to dest.

A related concept which does not help in your example but which is worth being aware of: Verilog-2001 introduced the "indexed part-select". An indexed part select specifies a base index and a width. The width is required to be constant but the base index does not need to be constant. The syntax for an indexed part select is vec[base+:width] or vec[base-:width].

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