Macro connect_dummy_tx 

macro_rules! connect_dummy_tx {
    ($entity:expr => $to:expr, $to_port_name:ident) => { ... };
    ($entity:expr => $to:expr, $to_port_name:ident, $to_index:expr) => { ... };
}

Create and connect a dummy TX port.

Use this when an input port is deliberately left unconnected in a particular topology. The dummy endpoint records that choice and marks the input as connected, preventing a runtime “not connected” error. It does not produce data: the input must never call get, because no transmitter will provide a value and the simulation may stall or terminate with unfinished work.