本文是將Default Event Loop：esp-idf/examples/system/esp_event/default_event_loop at release/v3.3 · espressif/esp-idf 例程內的README和代碼註釋翻譯一下，便於各位看官理解並理順思路。

README

事件循環庫Event Loop Library (‘esp_event’) 默認事件循環例程Default Event Loop Example

本例程是事件循環庫的一個示例。爲了保持簡單，示例僅限於使用默認事件循環。
默認事件循環是系統自帶的事件循環，在一般情況下已經夠用。
如果需要，用戶也可以參考 user_event_loops 例程創建用戶自定義的事件循環。

例程的內容如下：

事件的聲明與定義 (Declaring and Defining Events)

本例程展示瞭如何在頭文件中聲明event base和event ID，並在源文件中進行定義。
在頭文件中使用了 ESP_EVENT_DECLARE_BASE這個宏來聲明 event base, 而event IDs 在一個枚舉enum中進行聲明（參考esp-idf/event_source.h at release/v3.3 · espressif/esp-idf）。
。在源文件 main.c 中使用了 ESP_EVENT_DEFINE_BASE這個宏來定義event base.

創建默認事件循環 (Creating the Default Event Loop)

本例程中使用了esp_event_loop_create_default這個API來創建默認事件循環。

向默認事件循環發送事件 (Posting Events to the Default Event Loop)

簡單說，就是向默認事件循環發送事件相當於事件的handler依次執行隊列中的命令。使用API esp_event_post來向默認事件循環發送事件。例程中也展示瞭如何同時傳遞事件數據。

Handler的註冊與註銷 (Handler Registration/Unregistration)

本例程使用 esp_event_handler_register註冊了三個handler：
(1) 特定事件
(2) 特定event base的任意事件
(3) 任意事件
使用 esp_event_handler_unregister來註銷handler。註銷handler之後，即便事件此前已註冊的事件再次被髮送時，也不會再執行了。

例程解析 (Example Flow Explained)

以例程的LOG輸出來解釋：

I (276) default_event_loop: setting up
I (276) default_event_loop: starting event sources
I (276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: posting to default loop
I (276) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 1 out of 5
I (296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: timer_started_handler
I (306) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: timer_any_handler
I (316) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: all_event_handler
I (326) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: task_iteration_handler, executed 1 times
I (336) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler
I (806) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 2 out of 5
I (806) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: task_iteration_handler, executed 2 times
I (806) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler
I (1276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: posting to default loop
I (1276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_expiry_handler, executed 1 out of 3 times
I (1286) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_any_handler
I (1296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: all_event_handler
I (1306) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 3 out of 5
I (1316) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: unregistering task_iteration_handler
I (1316) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: task_iteration_handler, executed 3 times
I (1336) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler
I (1846) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 4 out of 5
I (1846) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler
I (2276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: posting to default loop
I (2276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_expiry_handler, executed 2 out of 3 times
I (2286) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_any_handler
I (2296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: all_event_handler
I (2346) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 5 out of 5
I (2346) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler
I (3276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: posting to default loop
I (3276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: posting to default loop
I (3286) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_expiry_handler, executed 3 out of 3 times
I (3296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_any_handler
I (3306) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: all_event_handler
I (3316) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: timer_stopped_handler
I (3326) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: deleted timer event source
I (3326) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: timer_any_handler
I (3336) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: all_event_handler
I (3346) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: deleting task event source

設置 (Setting)

本例程使用了兩個事件源：一個循環定時器和一個包含循環的任務。定時器在如下情況會產生事件：

定時器啓動
定時器間隔時間到
定時器停止
當任務每次循環時，也會產生事件。

除了如上事件對應的handler之外，還有一個handler，在任意事件發生的時候都會執行。
例程設定了定時器的重複執行次數和任務迭代次數。當定時器循環指定次數的時候，定時器會被停止。當任務迭代達到指定次數時，任務會被刪除。對於任務循環來說，還有另外一個設定：即當迭代達到某個次數的時候，對應的handler被註銷。

分步解析 (Step-by-Step Explanation)

如下輸出內容即爲關鍵點：
a.

I (297)  default_event_loop: setting up

此時默認事件循環已經被創建，同時各個事件handler已經被註冊。

I (276) default_event_loop: starting event sources
I (276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: posting to default loop
I (276) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 1 out of 5

兩個事件源已經啓動，並向默認事件循環發送事件。

I (296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: timer_started_handler
I (306) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: timer_any_handler
I (316) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STARTED: all_event_handler

I (326) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: task_iteration_handler, executed 1 times
I (336) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler

(b) 中發送的事件對應handler已被執行，另外
timer_started_handler， task_iteration_handler, timer_any_handler 與 all_event_handler 都被執行。

任意定時器事件均會觸發timer_any_handler的執行。可以看到定時器間隔時間到和定時器停止的時候也執行了timer_any_handler。

任意事件均會觸發all_event_handler的執行。所以在 TIMER_EVENTS:TIMER_EVENT_STARTED 和TASK_EVENTS:TASK_ITERATION_EVENT 兩個事件發生的時候可以看到它在執行。

對於定時器和任務事件，esp_event確保了他們是按照handler註冊的順序執行的。
如下輸出也是如此，事件的發送和handler的執行都完全依照上述註冊的順序。

...
I (1316) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: unregistering task_iteration_handler

此時 task_iteration_handler 已註銷, 因此當 TASK_EVENTS:TASK_ITERATION_EVENT發送時已不再執行。

I (1867) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 4 out of 5
I (1867) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handler

...

I (1846) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: posting to default loop, 4 out of 5
I (1846) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: all_event_handle

任務迭代事件繼續發送，但是隻有 all_event_handler 被執行。

...
I (3276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: posting to default loop
I (3276) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: posting to default loop
I (3286) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_expiry_handler, executed 3 out of 3 times
I (3296) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: timer_any_handler
I (3306) default_event_loop: TIMER_EVENTS:TIMER_EVENT_EXPIRY: all_event_handler
I (3316) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: timer_stopped_handler
I (3326) default_event_loop: TIMER_EVENTS:TIMER_EVENT_STOPPED: deleted timer event source

When the periodic timer expiry limit is reached, the event TIMER_EVENTS:TIMER_EVENT_STOPPED is posted to the loop. The periodic timer is consequently deleted in the handler timer_stopped_handler.
當定時器循環達到指定次數的時候，TIMER_EVENTS:TIMER_EVENT_STOPPED被髮送到事件循環，然後在timer_stopped_handler中定時器被刪除。

...
I (3346) default_event_loop: TASK_EVENTS:TASK_ITERATION_EVENT: deleting task event source
...

此時發送迭代事件的任務也被刪除。例程執行結束。

代碼：

/* esp_event (event loop library) basic example
   This example code is in the Public Domain (or CC0 licensed, at your option.)
   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/

#include "esp_log.h"

#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

#include "event_source.h"

static const char* TAG = "default_event_loop";

static char* get_id_string(esp_event_base_t base, int32_t id) {
    char* event = "";
    if (base == TIMER_EVENTS) {
        switch(id) {
            case TIMER_EVENT_STARTED:
            event = "TIMER_EVENT_STARTED";
            break;
            case TIMER_EVENT_EXPIRY:
            event = "TIMER_EVENT_EXPIRY";
            break;
            case TIMER_EVENT_STOPPED:
            event = "TIMER_EVENT_STOPPED";
            break;
        }
    } else {
        event = "TASK_ITERATION_EVENT";
    }
    return event;
}

/* 循環定時器相關的event base定義 */
ESP_EVENT_DEFINE_BASE(TIMER_EVENTS);

esp_timer_handle_t TIMER;


//定時器回調，回調中向默認事件循環發送事件
static void timer_callback(void* arg)
{
    ESP_LOGI(TAG, "%s:%s: posting to default loop", TIMER_EVENTS, get_id_string(TIMER_EVENTS, TIMER_EVENT_EXPIRY));
    ESP_ERROR_CHECK(esp_event_post(TIMER_EVENTS, TIMER_EVENT_EXPIRY, NULL, 0, portMAX_DELAY));
}

// 定時器啓動事件的Handler 
static void timer_started_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    ESP_LOGI(TAG, "%s:%s: timer_started_handler", base, get_id_string(base, id));
}


//定時器循環事件handler，每次發送定時到達事件，同時此回調記錄定時器執行次數，達到指定次數的時候會停止定時器併發送定時器停止事件。
static void timer_expiry_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    static int count = 0;

    count++;

    if (count >= TIMER_EXPIRIES_COUNT) {
        // 停止定時器
        ESP_ERROR_CHECK(esp_timer_stop(TIMER));

        ESP_LOGI(TAG, "%s:%s: posting to default loop", base, get_id_string(base, TIMER_EVENT_STOPPED));

        // 發送定時器停止事件
        ESP_ERROR_CHECK(esp_event_post(TIMER_EVENTS, TIMER_EVENT_STOPPED, NULL, 0, portMAX_DELAY));
    }

    ESP_LOGI(TAG, "%s:%s: timer_expiry_handler, executed %d out of %d times", base, get_id_string(base, id), count, TIMER_EXPIRIES_COUNT);
}


//任意定時器事件handler，在定時器開啓、時間到、停止時均會執行
static void timer_any_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    ESP_LOGI(TAG, "%s:%s: timer_any_handler", base, get_id_string(base, id));
}


//定時器停止事件handler。定時器停止之後即可安全刪除定時器。
static void timer_stopped_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    ESP_LOGI(TAG, "%s:%s: timer_stopped_handler", base, get_id_string(base, id));

    // 刪除定時器
    esp_timer_delete(TIMER);

    ESP_LOGI(TAG, "%s:%s: deleted timer event source", base, get_id_string(base, id));
}

/* 任務相關的event base定義 */
ESP_EVENT_DEFINE_BASE(TASK_EVENTS)

static void task_iteration_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    int iteration = *((int*) event_data);
    ESP_LOGI(TAG, "%s:%s: task_iteration_handler, executed %d times", base, get_id_string(base, id), iteration);
}

static void task_event_source(void* args)
{
    for(int iteration = 1; iteration <= TASK_ITERATIONS_COUNT; iteration++) {

        ESP_LOGI(TAG, "%s:%s: posting to default loop, %d out of %d", TASK_EVENTS,
                get_id_string(TASK_EVENTS, TASK_ITERATION_EVENT), iteration, TASK_ITERATIONS_COUNT);


     //發送任務迭代事件，迭代次數同時被傳遞給handler。請注意傳遞的數據是原數據的深拷貝。
        ESP_ERROR_CHECK(esp_event_post(TASK_EVENTS, TASK_ITERATION_EVENT, &iteration, sizeof(iteration), portMAX_DELAY));

        if (iteration == TASK_ITERATIONS_UNREGISTER){
            ESP_LOGI(TAG, "%s:%s: unregistering task_iteration_handler", TASK_EVENTS, get_id_string(TASK_EVENTS, TASK_ITERATION_EVENT));
            ESP_ERROR_CHECK(esp_event_handler_unregister(TASK_EVENTS, TASK_ITERATION_EVENT, task_iteration_handler));
        }

        vTaskDelay(pdMS_TO_TICKS(TASK_PERIOD));
    }

    vTaskDelay(pdMS_TO_TICKS(TASK_PERIOD));

    ESP_LOGI(TAG, "%s:%s: deleting task event source", TASK_EVENTS, get_id_string(TASK_EVENTS, TASK_ITERATION_EVENT));

    vTaskDelete(NULL);
}

/* 所有時間的handler*/
static void all_event_handler(void* handler_args, esp_event_base_t base, int32_t id, void* event_data)
{
    ESP_LOGI(TAG, "%s:%s: all_event_handler", base, get_id_string(base, id));
}

/* Example main */
void app_main(void)
{
    ESP_LOGI(TAG, "setting up");

    // Create the default event loop
    ESP_ERROR_CHECK(esp_event_loop_create_default());

    // 註冊特定定時器事件handler
    ESP_ERROR_CHECK(esp_event_handler_register(TIMER_EVENTS, TIMER_EVENT_STARTED, timer_started_handler, NULL));
    ESP_ERROR_CHECK(esp_event_handler_register(TIMER_EVENTS, TIMER_EVENT_EXPIRY, timer_expiry_handler, NULL));
    ESP_ERROR_CHECK(esp_event_handler_register(TIMER_EVENTS, TIMER_EVENT_STOPPED, timer_stopped_handler, NULL));

    //註冊所有定時器事件的handler，包括定時器開啓、時間到和停止事件
    ESP_ERROR_CHECK(esp_event_handler_register(TIMER_EVENTS, ESP_EVENT_ANY_ID, timer_any_handler, NULL));

    // 註冊迭代任務handler
    ESP_ERROR_CHECK(esp_event_handler_register(TASK_EVENTS, TASK_ITERATION_EVENT, task_iteration_handler, NULL));

    
//註冊所有事件的handler，定時器事件和任務迭代事件都會觸發它的執行
ESP_ERROR_CHECK(esp_event_handler_register(ESP_EVENT_ANY_BASE, ESP_EVENT_ANY_ID, all_event_handler, NULL));

    // 創建並啓動定時器事件源
    esp_timer_create_args_t timer_args = {
        .callback = &timer_callback,
    };

    ESP_ERROR_CHECK(esp_timer_create(&timer_args, &TIMER));

    ESP_LOGI(TAG, "starting event sources");

     // 創建任務事件源
    xTaskCreate(task_event_source, "task_event_source", 2048, NULL, uxTaskPriorityGet(NULL), NULL);

    ESP_ERROR_CHECK(esp_timer_start_periodic(TIMER, TIMER_PERIOD));

    // 發送定時器啓動事件
    ESP_LOGI(TAG, "%s:%s: posting to default loop", TIMER_EVENTS, get_id_string(TIMER_EVENTS, TIMER_EVENT_STARTED));
    ESP_ERROR_CHECK(esp_event_post(TIMER_EVENTS, TIMER_EVENT_STARTED, NULL, 0, portMAX_DELAY));
}

esp-idf 之事件循環(Event Loop)例程詳解

事件循環庫Event Loop Library (‘esp_event’) 默認事件循環例程Default Event Loop Example

事件的聲明與定義 (Declaring and Defining Events)

創建默認事件循環 (Creating the Default Event Loop)

向默認事件循環發送事件 (Posting Events to the Default Event Loop)

Handler的註冊與註銷 (Handler Registration/Unregistration)

例程解析 (Example Flow Explained)

設置 (Setting)

分步解析 (Step-by-Step Explanation)

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esp-idf 之事件循環(Event Loop)例程詳解

0.96寸OLED像素排列、漢字顯示和取模

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