常见错误

本页将讨论人们在使用 SpinalHDL 时可能出现的错误。

“main”线程中异常 java.lang.NullPointerException

控制台输出：

Exception in thread "main" java.lang.NullPointerException

代码示例：

val a = b + 1         // b can't be read at that time, because b isn't instantiated yet
val b = UInt(4 bits)

问题解释：

SpinalHDL 不是一种语言，它是一个 Scala 库，这意味着它遵循与 Scala 语言相同的通用规则。当您运行 SpinalHDL 硬件描述来生成相应的 VHDL/Verilog RTL 时，您的 SpinalHDL 硬件描述将作为 Scala 程序执行，并且执行程序到该行时， b 将是一个 null 空引用，这就是为什么你在这之前不能使用它的原因。

层次违例(Hierarchy violation)

SpinalHDL 编译器从层次结构的角度检查所有赋值是否合法。后续章节将详细阐述多个案例

Signal X can’t be assigned by Y

控制台输出：

Hierarchy violation : Signal X can't be assigned by Y

代码示例：

class ComponentX extends Component {
  ...
  val X = Bool()
  ...
}

class ComponentY extends Component {
  ...
  val componentX = new ComponentX
  val Y = Bool()
  componentX.X := Y // This assignment is not legal
  ...
}

class ComponentX extends Component {
  val io = new Bundle {
    val X = Bool() // Forgot to specify an in/out direction
  }
  ...
}

class ComponentY extends Component {
  ...
  val componentX = new ComponentX
  val Y = Bool()
  componentX.io.X := Y // This assignment will be detected as not legal
  ...
}

问题解释：

You can only assign input signals of subcomponents, else there is an hierarchy violation. If this issue happened, you probably forgot to specify the X signal’s direction.

Input signal X can’t be assigned by Y

控制台输出：

Hierarchy violation : Input signal X can't be assigned by Y

代码示例：

class ComponentXY extends Component {
  val io = new Bundle {
    val X = in Bool()
  }
  ...
  val Y = Bool()
  io.X := Y // This assignment is not legal
  ...
}

问题解释：

You can only assign an input signals from the parent component, else there is an hierarchy violation. If this issue happened, you probably mixed signals direction declaration.

Output signal X can’t be assigned by Y

控制台输出：

Hierarchy violation : Output signal X can't be assigned by Y

代码示例：

class ComponentX extends Component {
  val io = new Bundle {
    val X = out Bool()
  }
  ...
}

class ComponentY extends Component {
  ...
  val componentX = new ComponentX
  val Y = Bool()
  componentX.X := Y // This assignment is not legal
  ...
}

问题解释：

You can only assign output signals of a component from the inside of it, else there is an hierarchy violation. If this issue happened, you probably mixed signals direction declaration.