Hierarchy violation

Introduction

SpinalHDL will check that you never access a signal which is outside the current component range.

There is the list of signal which can be read within a component :

All direction less signals defined in the same component
All in/out/inout signals of the current component
All in/out/inout signals of children components

There is the list of signals which can be assigned within a component :

All direction less signals defined in the same component
All out/inout signals of the current component
All in/inout signals of children components

If an HIERARCHY VIOLATION appear, it mean that one of the above rules was violated.

Example

The following code :

class TopLevel extends Component {
  val io = new Bundle {
    val a = in UInt(8 bits)
  }
  val tmp = U"x42"
  io.a := tmp
}

will throw :

HIERARCHY VIOLATION : (toplevel/io_a : in UInt[8 bits]) is drived by (toplevel/tmp :  UInt[8 bits]), but isn't accessible in the toplevel component.
  ***
  Source file location of the `io.a := tmp` via the stack trace
  ***

A fix could be :

class TopLevel extends Component {
  val io = new Bundle {
    val a = out UInt(8 bits)
  }

  io.a := 42
}