Semaphore Task Synchronization
The eCos semaphore example is similar to a push button light
switch using an LED for the light. The following example has two tasks:
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 shows the
button used in this example.

Figure 11-1. Arcom board add-on module’s SW0 button
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. Upon receiving the signal, the consumer task
outputs a message and toggles the green LED.
The main function, cyg_user_start, starts by initializing the LED
by calling ledInit. Next, the
semaphore is initialized with a call to cyg_semaphore_init. The initial value of the
semaphore, semButton, is set to zero
so that the consumer task that is waiting does not execute until the
semaphore is signaled by the producer task. Lastly, the two tasks are
created and resumed, as in the prior example, and then a message is
output signifying the start of the program.
#include <cyg/kernel/kapi.h> #include <cyg/infra/diag.h> #include "led.h" cyg_sem_t semButton; /********************************************************************** * * Function: cyg_user_start * * Description: Main routine for the eCos semaphore program. This * function ...