Книга: Real-Time Concepts for Embedded Systems
15.7.5 Sending High Priority Data between Tasks
15.7.5 Sending High Priority Data between Tasks
In many situations, the communication between tasks can carry urgent data. Urgent data must be processed in a timely fashion and must be distinguished from normal data. This process is accomplished by using signals and an urgent data message queue, as shown in Figure 15.21. For the sake of this example, the reader should assume the message queues shown in Figure 15.21 do not support a priority message delivery mechanism.
Figure 15.21: Using signals for urgent data communication.
As Chapter 8 describes, one task uses a signal to notify another of the arrival of urgent data. When the signal arrives, the receiving task diverts from its normal execution and goes directly to the urgent data message queue. The task processes messages from this queue ahead of messages from other queues because the urgent data queue has the highest priority. This task must install an asynchronous signal handler for the urgent data signal in order to receive it. The reason the signal for urgent data notification is deploying is because the task does not know of the arrival of urgent data unless the task is already waiting on the message queue.
The producer of the urgent data, which can be either a task or an ISR, inserts the urgent messages into the predefined urgent data message queue. The source signals the recipient of the urgent data. The signal interrupts the normal execution path of the recipient task, and the installed signal handler is invoked. Inside this signal handler, urgent messages are read and processed.
In this design pattern, urgent data is maintained in a separate message queue although most RTOS-supplied message queues support priority messages. With a separate message queue for urgent data, the receiver can control how much urgent data it is willing to accept and process, i.e., a flow control mechanism.
Оглавление книги
- 15.7.1 Data Transfer with Flow Control
- 15.7.2 Asynchronous Data Reception from Multiple Data Communication Channels
- 15.7.3 Multiple Input Communication Channels
- 15.7.4 Using Condition Variables to Synchronize between Readers and Writers
- 15.7.5 Sending High Priority Data between Tasks
- 15.7.6 Implementing Reader-Writer Locks Using Condition Variables
- Информация заголовочной страницы (Database header)
- Database dialect
- DATABASE CACHE SIZE
- SERVER PRIORITY CLASS
- Data sending and control session
- SCTP DATA chunk
- Data Binding Using the GridView Control
- Interbase DataPump
- GetDataBack
- Работа с DataRow
- 10.3.2 Automatic Highlighting and Coloring
- 8.4.2. Sending and Receiving Messages