Development Guidelines

• Available APIs
• How to Develop
• Development Example
  • Example Description
  • Sample Code
  • Verification

Available APIs

How to Develop

The typical event development process is as follows:

1. Initialize an event control block.
2. Block a read event control block.
3. Write related events.
4. Wake up a blocked task, read the event, and check whether the event meets conditions.
5. Handle the event control block.
6. Destroy an event control block.

NOTE:

• When an event is read or written, the 25th bit of the event is reserved and cannot be set.
• Repeated writes of the same event are treated as one write.

Development Example

Example Description

In this example, run the Example_TaskEntry task to create the Example_Event task. Run the Example_Event task to read an event to trigger task switching. Run the Example_TaskEntry task to write an event. You can understand the task switching during event operations based on the sequence in which logs are recorded.

1. Create the Example_Event task in the Example_TaskEntry task with a higher priority than the Example_TaskEntry task.
2. Run the Example_Event task to read event 0x00000001. Task switching occurs to execute the Example_TaskEntry task.
3. Run the Example_TaskEntry task to write event 0x00000001. Task switching occurs to execute the Example_Event task.
4. The Example_Event task is executed.
5. The Example_TaskEntry task is executed.

Sample Code

The sample code is as follows:

#include "los_event.h"
#include "los_task.h"
#include "securec.h"

/* Task ID*/
UINT32 g_testTaskId;

/* Event control structure*/ 
EVENT_CB_S g_exampleEvent;

/* Type of the wait event*/
#define EVENT_WAIT 0x00000001

/* Example task entry function*/
VOID Example_Event(VOID)
{
    UINT32 ret;
    UINT32 event;

    /* Set a timeout period for event reading to 100 ticks. If the specified event is not read within 100 ticks, the read operation times out and the task is woken up.*/
    printf("Example_Event wait event 0x%x \n", EVENT_WAIT);

    event = LOS_EventRead(&g_exampleEvent, EVENT_WAIT, LOS_WAITMODE_AND, 100);
    if (event == EVENT_WAIT) {
        printf("Example_Event,read event :0x%x\n", event);
    } else {
        printf("Example_Event,read event timeout\n");
    }
}

UINT32 Example_TaskEntry(VOID)
{
    UINT32 ret;
    TSK_INIT_PARAM_S task1;

    /* Initialize the event.*/ 
    ret = LOS_EventInit(&g_exampleEvent);
    if (ret != LOS_OK) {
        printf("init event failed .\n");
        return -1;
    }

    /* Create a task.*/ 
    (VOID)memset_s(&task1, sizeof(TSK_INIT_PARAM_S), 0, sizeof(TSK_INIT_PARAM_S));
    task1.pfnTaskEntry = (TSK_ENTRY_FUNC)Example_Event;
    task1.pcName       = "EventTsk1";
    task1.uwStackSize  = OS_TSK_DEFAULT_STACK_SIZE;
    task1.usTaskPrio   = 5;
    ret = LOS_TaskCreate(&g_testTaskId, &task1);
    if (ret != LOS_OK) {
        printf("task create failed.\n");
        return LOS_NOK;
    }

    /* Write the task wait event (g_testTaskId). */
    printf("Example_TaskEntry write event.\n");

    ret = LOS_EventWrite(&g_exampleEvent, EVENT_WAIT);
    if (ret != LOS_OK) {
        printf("event write failed.\n");
        return LOS_NOK;
    }

    /* Clear the flag.*/ 
    printf("EventMask:%d\n", g_exampleEvent.uwEventID);
    LOS_EventClear(&g_exampleEvent, ~g_exampleEvent.uwEventID);
    printf("EventMask:%d\n", g_exampleEvent.uwEventID);

    /* Delete the task.*/ 
    ret = LOS_TaskDelete(g_testTaskId);
    if (ret != LOS_OK) {
        printf("task delete failed.\n");
        return LOS_NOK;
    }

    return LOS_OK;
}

Verification

The development is successful if the return result is as follows:

Example_Event wait event 0x1 
Example_TaskEntry write event.
Example_Event,read event :0x1
EventMask:1
EventMask:0