Macro connect_dummy_rx 

macro_rules! connect_dummy_rx {
    ($from:expr, $from_port_name:ident => $engine:expr, $clock:expr, $entity:expr) => { ... };
    ($from:expr, $from_port_name:ident, $from_index:expr => $engine:expr, $clock:expr, $entity:expr) => { ... };
}

Create and connect a dummy RX port.

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