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作用域违例(Scope violation)

简介

SpinalHDL将会检查没有信号会在超出其定义的作用域之外被赋值使用。这个错误不容易触发，因为它需要一些特定的元硬件描述技巧。

示例

下面的代码：

class TopLevel extends Component {
  val cond = Bool()

  var tmp : UInt = null
  when(cond) {
    tmp = UInt(8 bits)
  }
  tmp := U"x42"
}

会报错：

SCOPE VIOLATION : (toplevel/tmp :  UInt[8 bits]) is assigned outside its declaration scope at
  ***
  Source file location of the tmp := U"x42" via the stack trace
  ***

一个可能的修复方法是：

class TopLevel extends Component {
  val cond = Bool()

  var tmp : UInt = UInt(8 bits)
  when(cond) {

  }
  tmp := U"x42"
}