- The wait statement causes the suspension of a process statement or a procedure
 - wait [sensitivity_clause] [condition_clause]
[timeout_clause];
- sensitivity_clause ::= on signal_name {, signal_name}
    wait on CLOCK;
 - condition_clause ::= until boolean_expression
    wait until Clock = '1';
 - timeout_clause ::= for time_expression
    wait for 150 ns;