The wait statement is a statement that causes suspension of a process or a procedure.

Syntax:

[ label: ] wait [ on signal_list ] [ until condition ] [ for time_expression ]; 

Description:

The wait statement suspends the execution of the process or procedure in which it is specified. Resuming the process or procedure depends on meting the condition(s) specified in the wait statement.

The syntax of the wait statement allows to use it without any condition. Such a statement is equivalent to wait until true, which suspends a process forever and will never resume.

Example:

Pr1: process
begin
  wait until Clk'event and Clk = '1';
  Q <= A;
  wait for 10 ns;
  Q <= B;
  wait on C;
  Q <= C;
  wait;
end process;   

Notes:

• A process with a sensitivity list may not contain any wait statements.
• wait for, wait on and wait are not synthesizable
• wait until is synthesizable only when used to synchronize a process to a clock edge (e.g.: wait until Clock = '1')

See also:

Process, Sensitivity list