We use the term processes in the SystemC sense to cover both SC_THREAD and SC_METHOD.

The busThread is a SC_THREAD. It sits in a perpetual loop. It first marks the transmit buffer as empty (on reset the flags are cleared, so the buffer will appear full).

	Note
	The 16450 UART describes two flags for transmit buffer status, one to indicate that the transmit holding register is empty and a second to indicate that the internal transmit buffer register is empty. For simplicity, this model does not model a separate internal register (effectively a one byte FIFO), so both flags are set and cleared together.

If the transmit buffer empty interrupt is enabled, the thread generates an interrupt to indicate that the buffer is empty.

The thread then waits until it is notified via the SystemC event txReceived that a byte is in the buffer to be sent. This event will be triggered by the busWrite callback when a value is written into the transmit holding register.

	Note
	It might be thought that a SystemC SC_METHOD sensitive to txReceived would be more efficient. That would certainly be suitable in this implementation. However this is a virtual function, and when we reimplement later to add timing, we will wish to call wait, which requires a SystemC SC_THREAD.

The second process, rxMethod is a SystemC SC_METHOD, sensitive to characters appearing in the Rx buffer. The character is read into the read buffer register and the line status data ready flag is set to indicate availability.

If the receive data interrupt is enabled, an interrupt is asserted to indicate data availability.