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Programming Embedded Systems, 2nd Edition
book

Programming Embedded Systems, 2nd Edition

by Michael Barr, Anthony Massa
October 2006
Intermediate to advanced content levelIntermediate to advanced
336 pages
9h 13m
English
O'Reilly Media, Inc.
Content preview from Programming Embedded Systems, 2nd Edition

Semaphore Task Synchronization

The Linux semaphore example is similar to a push button light switch, using an LED for the light, as was the case in the eCos semaphore example. There are two tasks in this example: a producer and a consumer. The producer task, producerTask, monitors the button labeled SW0 on the Arcom board’s add-on module. Figure 11-1 in Chapter 11 shows the button used in this example.

When the SW0 button is pressed, the producer task signals the consumer task using a semaphore. The consumer, consumerTask, waits for the semaphore signal from the producer task; once received, the consumer task outputs a message and toggles the green LED.

The main function first initializes the LED by calling ledInit. Next, the semaphore is initialized with a call to sem_init. The initial value of the semaphore, semButton, is set to zero by the last parameter so that the consumer task that is waiting does not execute until the semaphore is signaled by the producer task. The second parameter notifies the operating system that this semaphore may be used by this process only. Lastly, the two tasks are created and a message is output signifying the start of the program.

#include <stdio.h> #include <pthread.h> #include <semaphore.h> #include "led.h" sem_t semButton; /********************************************************************** * * Function: main * * Description: Main routine for the Linux semaphore example. This * function creates the semaphore and then the increment * and decrement ...
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Publisher Resources

ISBN: 0596009836Supplemental ContentErrata Page