nRF52(SDK12)添加定时器任务

在裸机程序中，有timer例子，直接使用没有任何问题，但是不能直接用在BLE程序中。在BLE程序中使用就有些麻烦，BLE本身也使用了定时器，如果APP再使用算是借用。SDK12的BLE例子中也没有找到完整的例子。网上找到nrf52 Application Timer和nrf52-添加定时任务。
前者例子：

// General application timer settings.
#define APP_TIMER_PRESCALER             16    // Value of the RTC1 PRESCALER register.
#define APP_TIMER_MAX_TIMERS            2     // Maximum number of timers in this application.
#define APP_TIMER_OP_QUEUE_SIZE         3     // Size of timer operation queues.

static app_timer_id_t                   m_led_a_timer_id;

static void lfclk_request(void)
{
    uint32_t err_code = nrf_drv_clock_init(NULL);
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request();
}

// Timeout handler for the repeated timer
static void timer_a_handler(void * p_context)
{
  nrf_drv_gpiote_out_toggle(LED_1_PIN);
}


// Create timers
static void create_timers()
{   
    uint32_t err_code;

    // Create timers
    err_code = app_timer_create(&m_led_a_timer_id,
                                APP_TIMER_MODE_REPEATED,
                                timer_a_handler);
    APP_ERROR_CHECK(err_code);
}

int main()
{
	// Request LF clock.
	lfclk_request();
  
	// Initialize the application timer module.
	APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_MAX_TIMERS,      APP_TIMER_OP_QUEUE_SIZE, false);

  create_timers();
  
  uint32_t err_code = app_timer_start(m_led_a_timer_id, APP_TIMER_TICKS(200, APP_TIMER_PRESCALER), NULL);
  APP_ERROR_CHECK(err_code);
  while(1);
}

在experimental_ble_app_buttonless_dfu找到一些APP Timer使用的蛛丝马迹，重点有timer_init和application_timers_start两个函数。

/**@brief Function for the Timer initialization.
 *
 * @details Initializes the timer module.
 */
static void timers_init(void)
{
    // Initialize timer module, making it use the scheduler
    APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_OP_QUEUE_SIZE, false);
    // Create timers.

    /* YOUR_JOB: Create any timers to be used by the application.
                 Below is an example of how to create a timer.
                 For every new timer needed, increase the value of the macro APP_TIMER_MAX_TIMERS by
                 one.
    uint32_t err_code;
    err_code = app_timer_create(&m_app_timer_id, APP_TIMER_MODE_REPEATED, handle);
    APP_ERROR_CHECK(err_code);
    */
}
/**@brief Function for starting timers.
 */
static void application_timers_start(void)
{
    /* YOUR_JOB: Start your timers. below is an example of how to start a timer. 
    uint32_t err_code;
    err_code = app_timer_start(m_app_timer_id, TIMER_INTERVAL, NULL);
    APP_ERROR_CHECK(err_code);
	 */
}

将其uncomment之后并不能正常使用，BLE都搜索不到了。Debug之后定位到app_timer_create反回了一个0x08，而不是成功的0x00。

过一段时间再去搜索原因，有一个帖子提到需要使用APP_TIMER_DEF(m_app_timer_id);的方式取代如下方式：

static app_timer_id_t m_timer_id;

来源：https://devzone.nordicsemi.com/f/nordic-q-a/17936/migrating-from-sdk8-to-sdk12-app_timer_create-crashes

这样就好了，完整如下：


//static app_timer_id_t m_app_timer_id;
APP_TIMER_DEF(m_app_timer_id);

/**@brief Function for the Timer initialization.
 *
 * @details Initializes the timer module.
 */
static void timers_init(void)
{
    // Initialize timer module, making it use the scheduler
    APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_OP_QUEUE_SIZE, false);
    // Create timers.

    /* YOUR_JOB: Create any timers to be used by the application.
                 Below is an example of how to create a timer.
                 For every new timer needed, increase the value of the macro APP_TIMER_MAX_TIMERS by
                 one.
     */
    uint32_t err_code;
    err_code = app_timer_create(&m_app_timer_id, APP_TIMER_MODE_REPEATED, handle);
    APP_ERROR_CHECK(err_code);
}

#define TIMER_INTERVAL 20

/**@brief Function for starting timers.
 */
static void application_timers_start(void)
{
    /* YOUR_JOB: Start your timers. below is an example of how to start a timer.  */
    uint32_t err_code;
    err_code = app_timer_start(m_app_timer_id, TIMER_INTERVAL, NULL);
    APP_ERROR_CHECK(err_code);

}

其他被证实为假的假设：

APP_TIMER_MAX_TIMERS需要+1，在sdk12版本中，似乎并没有使用到该宏；
需要nrf_drv_clock_lfclk_request，实测并不需要调用；

nRF52(SDK12)添加定时器任务

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