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Assertions

In addition to Scala run-time assertions, you can add hardware assertions using the following syntax:

assert(assertion : Bool, message : String = null, severity: AssertNodeSeverity = Error)

Severity levels are:

Name	Description
NOTE	Used to report an informative message
WARNING	Used to report an unusual case
ERROR	Used to report an situation that should not happen
FAILURE	Used to report a fatal situation and close the simulation

One practical example could be to check that the valid signal of a handshake protocol never drops when ready is low:

class TopLevel extends Component {
  val valid = RegInit(False)
  val ready = in Bool()

  when(ready) {
    valid := False
  }
  // some logic

  assert(
    assertion = !(valid.fall && !ready),
    message   = "Valid dropped when ready was low",
    severity  = ERROR
  )
}