Event

Table of Contents

• Features Supported
• Features NOT Supported
• Important Usage Guidelines
• Example Usage
• API

Features Supported

• APIs to construct and destruct Events
• APIs to set, get or clear bits and wait for bits

Features NOT Supported

• These APIs are not implemented for no-RTOS. Error will be returned if these APIs called using no-RTOS.

Important Usage Guidelines

• EventP_waitBits should not be called within ISR context. It can be called from task context.
• Setting or clearing the Event bits is a non-deterministic operation and FreeRTOS does not allow non-deterministic operations to be performed in interrupts or from critical sections. If EventP_setBits or EventP_clearBits is called from an ISR, a message is sent to RTOS daemon task to perform the operation in the context of daemon task. If the set or clear operation is required to be completed immediately, then the priority of RTOS daemon task must be higher than the priority of task waiting for the Event bits. The priority of RTOS daemon task is set by the configTIMER_TASK_PRIORITY in FreeRTOSConfig.h file.
• The actual current value of Event bits returned from EventP_waitBits and EventP_getBits can be different from returned value if an interrupt or a higher priority task modifies the value between the calling task leaving blocked state and exiting this API.

Example Usage

Include the below file to access the APIs

#include <kernel/dpl/EventP.h>

Example usage to define an Event

/* Event objects, typically these are global's */
EventP_Object gMyEvent;
 
/* Event bits */
/* Event bit mask upto 24 bits */
#define EVENT_BIT_PING (0x000001u)
#define EVENT_BIT_PONG (0x000002u)

Example usage to create an Event

    status = EventP_construct(&gMyEvent);

Example usage to set and wait for bits across two tasks

void task1(void *args)
{
    int32_t status;
    uint32_t eventBits;
 
    /* Set PING bit from task1 */
    status = EventP_setBits(&gMyEvent, EVENT_BIT_PING);
 
    /* Reading the Event Bits */
    status = EventP_getBits(&gMyEvent, &eventBits);
 
    /* Wait for PONG but to be set from task2. PING bit was already set */
    status = EventP_waitBits(&gMyEvent, (EVENT_BIT_PING | EVENT_BIT_PONG), 0, 1, SystemP_WAIT_FOREVER, &eventBits);
 
    /* Clearing the PING and PONG bits */
    status = EventP_clearBits(&gMyEvent, (EVENT_BIT_PING | EVENT_BIT_PONG));
}

void task2(void *args)
{
    int32_t status;
    uint32_t eventBits;
 
    /* Wait for PING but to be set from task1*/
    status = EventP_waitBits(&gMyEvent, EVENT_BIT_PING, 0, 1, SystemP_WAIT_FOREVER, &eventBits);
 
    /* Set PONG bit from task2 */
    status = EventP_setBits(&gMyEvent, EVENT_BIT_PONG);
 
}

API

APIs for Event