## 位宽不匹配(Width mismatch)

### 一、简介

SpinalHDL会检查赋值两侧的操作和信号有相同的位宽。

### 二、分配赋值例子

下述代码：
```Scala
class TopLevel extends Component {
  val a = UInt(8 bits)
  val b = UInt(4 bits)
  b := a
}
```
将会报错：
```
WIDTH MISMATCH on (toplevel/b :  UInt[4 bits]) := (toplevel/a :  UInt[8 bits]) at
  ***
  Source file location of the OR operator via the stack trace
  ***
```
可以修复为：
```Scala
class TopLevel extends Component {
  val a = UInt(8 bits)
  val b = UInt(4 bits)
  b := a.resized
}
```

### 三、操作实例

下述代码：
```Scala
class TopLevel extends Component {
  val a = UInt(8 bits)
  val b = UInt(4 bits)
  val result = a | b
}

```
将会报错：
```
WIDTH MISMATCH on (UInt | UInt)[8 bits]
- Left  operand : (toplevel/a :  UInt[8 bits])
- Right operand : (toplevel/b :  UInt[4 bits])
  at
  ***
  Source file location of the OR operator via the stack trace
  ***
```
可修复为：
```Scala
class TopLevel extends Component {
  val a = UInt(8 bits)
  val b = UInt(4 bits)
  val result = a | (b.resized)
}
```