Entities may contain statements, but they can only be :
- Concurrent assertion statements
- Passive concurrent procedure calls
- Passive process statements
PORT (a, b: IN BIT; select: IN BIT;
ASSERT NOT(a=b) REPORT “a equals b”
An entity can contain passive statements to perform actions such as timing or validity checks at the interface of a component. Assertion statements in an entity, for example, may be used to check that setup and hold requirements are satisfied.
A passive statement is one which does not change the state of the system being simulated. For example, the execution of a passive statement does not lead to any signal assignments.