The existing UART module processes interrupts, but does not generate an external interrupt signal. To generate an interrupt signal, UartDecoupSC is further extended by a new derived class, UartIntrSC, which provides a signal port and a new thread to drive that signal port

An extra thread is required, because both the rxMethod and busThread processes may wish to drive signals, but SystemC requires that a signal is driven by a single process. Just as in hardware design a simple wire would not normally have more than one driver.

The new process communicates with the existing processes via a FIFO internal to the UART, allowing rxMethod and busThread to both request interrupt activity and for those requests to be processed in the order they were generated.