TABLE OF CONTENTS Tasks communicate with one another so that they can pass information to each other and coordinate their activities in a multithreaded embedded application. Communication can be signal-centric, data-centric, or both. In signal-centric communication , all necessary information is conveyed within the event signal itself. In data-centric communication , information is carried within the transferred data. When the two are combined, data transfer accompanies event notification.
When communication involves data flow and is unidirectional, this communication model is called loosely coupled communication. In this model, the data producer does not require a response from the consumer. Figure 15.4 illustrates an example of loosely coupled communication.
For example, an ISR for an I/O device retrieves data from a device and routes the data to a dedicated processing task. The ISR neither solicits nor requires feedback from the processing task. By contrast, in tightly coupled communication , the data movement is bidirectional. The data producer synchronously waits for a response to its data transfer before resuming execution, or the response is returned asynchronously while the data producer continues its function.
In tightly coupled communication, as shown in Figure 15.5, task #1 sends data to task #2 using message queue #2 and waits for confirmation to arrive at message queue #1. The data communication is bidirectional. It is necessary to use a message queue for confirmations because the confirmation should contain enough...
