Question about stopping all the timers that are used in the application.

[Rajat]

Hi Everyone

I have got 3 timers in my application. 

1 is repeated , and other two are Single shot which are ran from the inputs to the 1st Repeated timer.

The repeated keeps checking the UART for a byte , once the byte is received , One single shot timer is started , which on expiry turn One of my sensor OFF and inside the handler starts another single shot timer which again turns ON the sensor after 1 hour. 

If i stop the repeated timer when i turn OFF the Sensor , and start the Timer when I turn ON the sensor again. The whole thing just comes to a halt and it doesn't work anymore.

I have fixed this issue by using a timer of 10 seconds , which does literally nothing but keep repeating after 10 seconds, but i am not sure if the theory is correct or not.

""If all the timers have been turned OFF , the RTC goes to deep-sleep and it doesn't count anymore and to keep the RTC alive , i have used a repeated timer as desribed above.

It works in this configuration , but i am not sure if the reasoning is correct or not.""

Kindly help me understand this behavior.

Thanks 

Rajat

[Edvin]

Can you please specify a few things:
What is your LFCLK source? And what is your app_timer prescaler? 

As you can see from the documentation of the RTC, the resolution is not necessarily even 10m:

https://www.nordicsemi.com/DocLib/Content/Product_Spec/nRF52840/latest/rtc?664#concept_rvn_vkj_sr

I don't think I fully understand your requirements, but you need to have a timer running at all times, or do you not?

BR,

Edvin

[Rajat]

I am using BLE , so that by default would init the lfclk and app timer prescaler is 15 .

No , i need restart the stopped timer after certain duration of expiry of a different timer. . Works well for less than 10 minutes , but for a greater duration , it doesn't.

[Rajat]

No , It doesn't work for me.

[Rajat]

Just to be sure , I need to make this definition 1 in the SDKCONFIG.h file , right?

[Edvin]

Is it possible to send a project that can reproduce what you are seeing? I am not sure I understand exactly what you are doing and what the issue is. 

If you can zip the project folder, and upload it here together with some instructions on how to reproduce the issues, that would be great.

Best regards,

Edvin

[Rajat]

Let me make it very simple .

I have a repeated timer 

T1 interval on boot is 5 seconds .

When the timer expires , t1 timer handler will be called.

static void
t1_timer_handler (void *p_context)
{

    app_sched_event_put (NULL, 0, manual_sensor_handler);
    app_timer_stop (t1_timer_id);
    app_timer_start(t1_timer_id, APP_TIMER_TICKS(600000), NULL);  //10 minutes = 600seconds
    
    /*Problem : t1 timer is not restarting after 10 minutes. Works perfectly if the
    time is less than 10 minutes*/
}

int main(void)
{
ble_init ();
app_timer_init();
APP_SCHED_INIT (APP_TIMER_SCHED_EVENT_DATA_SIZE, 10);
app_timer_create (&t1_timer_id, APP_TIMER_MODE_REPEATED, t1_timer_handler);
app_timer_start (t1_timer_id, T1_INTERVAL, NULL);
    
while (1)
    {
        nrf_pwr_mgmt_run ();
        app_sched_execute ();
    }
}

[Edvin]

Thank you! Nice and simple. But I need to see your app_timer_init() and your sdk_config.h file.I assume that your nrf_pwr_mgmt_run() is unmodified? I also assume your app_sched_execute() is unmodified?

I believe you should switch place on app_sched_execute() and nrf_pwr_mgmt_run(), by the way, since now, you will not execute the scheduler until you wake up from nrf_pwr_mgmt_run()

This is the first time I can see that you are using the app scheduler, which is quite relevant for your application.

So I will still need to know your prescaler on your app_timer. You can either send me your project, or a project that can reproduce the issue that you see in order to help you in a timely manner. Alternatively, you can give me your sdk_config.h and app_timer_init() function, as long as you didn't change anything in the app_timer SDK files. But if I can't replicate the issue, I would have to give you the same answer again: "please send a project that can replicate this issue".

Best regards,

Edvin

[Rajat]

1. Yes , both the functions app_sched_execute() and nrf_pwr_mgmt_run() are unmodified.

2. Okay , i will try switching places of both the functions.

3. The project is very huge , as it uses sensors and LoRa and many other peripherals. It would be difficult for you to reproduce the same on your side.

4. The prescaler value is 15 . 

5. I haven't changed the app_timer_init() function at all .

6. I am attaching my SDKCONFIG.h file , You can have a look at that.

4034.sdk_config.h

[Rajat]

7. Here is the file for app_timer_init() function from the SDK15.0

Fullscreen 8132.app_timer.c Download

/**
 * Copyright (c) 2012 - 2018, Nordic Semiconductor ASA
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 * 
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 * 
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 * 
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 * 
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 */
#include "sdk_common.h"
#if NRF_MODULE_ENABLED(APP_TIMER)
#include "app_timer.h"
#include <stdlib.h>
#include "nrf.h"
#include "nrf_peripherals.h"
#include "nrf_soc.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#if APP_TIMER_CONFIG_USE_SCHEDULER
#include "app_scheduler.h"
#endif

#define RTC1_IRQ_PRI            APP_TIMER_CONFIG_IRQ_PRIORITY               /**< Priority of the RTC1 interrupt (used for checking for timeouts and executing timeout handlers). */
#define SWI_IRQ_PRI             APP_TIMER_CONFIG_IRQ_PRIORITY               /**< Priority of the SWI  interrupt (used for updating the timer list). */

// The current design assumes that both interrupt handlers run at the same interrupt level.
// If this is to be changed, protection must be added to prevent them from interrupting each other
// (e.g. by using guard/trigger flags).
STATIC_ASSERT(RTC1_IRQ_PRI == SWI_IRQ_PRI);

#define MAX_RTC_COUNTER_VAL     0x00FFFFFF                                  /**< Maximum value of the RTC counter. */

#define RTC_COMPARE_OFFSET_MIN  3                                           /**< Minimum offset between the current RTC counter value and the Capture Compare register. Although the nRF51 Series User Specification recommends this value to be 2, we use 3 to be safer.*/

#define MAX_RTC_TASKS_DELAY     47                                          /**< Maximum delay until an RTC task is executed. */

#ifdef EGU_PRESENT
#define SWI_PART(_id) CONCAT_2(SWI,_id)
#define EGU_PART(_id) CONCAT_2(_EGU,_id)
#define SWI_IRQ_n(_id) CONCAT_3(SWI_PART(_id), EGU_PART(_id),_IRQn)
#define SWI_IRQ_Handler_n(_id) CONCAT_3(SWI_PART(_id), EGU_PART(_id),_IRQHandler)
#else //EGU_PRESENT
#define SWI_IRQ_n(_id) CONCAT_3(SWI,_id,_IRQn)
#define SWI_IRQ_Handler_n(_id) CONCAT_3(SWI,_id,_IRQHandler)
#endif

#define SWI_IRQn SWI_IRQ_n(APP_TIMER_CONFIG_SWI_NUMBER)
#define SWI_IRQHandler SWI_IRQ_Handler_n(APP_TIMER_CONFIG_SWI_NUMBER)


#define MODULE_INITIALIZED (m_op_queue.size != 0)                           /**< Macro designating whether the module has been initialized properly. */

/**@brief Timer node type. The nodes will be used form a linked list of running timers. */
typedef struct
{
    uint32_t                    ticks_to_expire;                            /**< Number of ticks from previous timer interrupt to timer expiry. */
    uint32_t                    ticks_at_start;                             /**< Current RTC counter value when the timer was started. */
    uint32_t                    ticks_first_interval;                       /**< Number of ticks in the first timer interval. */
    uint32_t                    ticks_periodic_interval;                    /**< Timer period (for repeating timers). */
    bool                        is_running;                                 /**< True if timer is running, False otherwise. */
    app_timer_mode_t            mode;                                       /**< Timer mode. */
    app_timer_timeout_handler_t p_timeout_handler;                          /**< Pointer to function to be executed when the timer expires. */
    void *                      p_context;                                  /**< General purpose pointer. Will be passed to the timeout handler when the timer expires. */
    void *                      next;                                       /**< Pointer to the next node. */
} timer_node_t;

STATIC_ASSERT(sizeof(timer_node_t) == APP_TIMER_NODE_SIZE);

/**@brief Set of available timer operation types. */
typedef enum
{
    TIMER_USER_OP_TYPE_NONE,                                                /**< Invalid timer operation type. */
    TIMER_USER_OP_TYPE_START,                                               /**< Timer operation type Start. */
    TIMER_USER_OP_TYPE_STOP,                                                /**< Timer operation type Stop. */
    TIMER_USER_OP_TYPE_STOP_ALL                                             /**< Timer operation type Stop All. */
} timer_user_op_type_t;

/**@brief Structure describing a timer start operation. */
typedef struct
{
    uint32_t ticks_at_start;                                                /**< Current RTC counter value when the timer was started. */
    uint32_t ticks_first_interval;                                          /**< Number of ticks in the first timer interval. */
    uint32_t ticks_periodic_interval;                                       /**< Timer period (for repeating timers). */
    void *   p_context;                                                     /**< General purpose pointer. Will be passed to the timeout handler when the timer expires. */
} timer_user_op_start_t;

/**@brief Structure describing a timer operation. */
typedef struct
{
    timer_user_op_type_t op_type;                                             /**< Id of timer on which the operation is to be performed. */
    timer_node_t *       p_node;
    union
    {
        timer_user_op_start_t start;                                        /**< Structure describing a timer start operation. */
    } params;
} timer_user_op_t;

/**@brief Structure describing a timer operations queue.
 *
 * @details This queue will hold timer operations issued by the application
 *          until the timer interrupt handler processes these operations.
 */
typedef struct
{
    uint8_t           first;                                                    /**< Index of first entry to have been inserted in the queue (i.e. the next entry to be executed). */
    uint8_t           last;                                                     /**< Index of last entry to have been inserted in the queue. */
    uint8_t           size;                                                     /**< Queue size. */
    timer_user_op_t   user_op_queue[APP_TIMER_CONFIG_OP_QUEUE_SIZE+1];          /**< Queue buffer. */
} timer_op_queue_t;

STATIC_ASSERT(sizeof(timer_op_queue_t) % 4 == 0);

#define CONTEXT_QUEUE_SIZE_MAX      (2)

static timer_op_queue_t              m_op_queue;                                /**< Timer operations queue. */
static timer_node_t *                mp_timer_id_head;                          /**< First timer in list of running timers. */
static uint32_t                      m_ticks_latest;                            /**< Last known RTC counter value. */
static uint32_t                      m_ticks_elapsed[CONTEXT_QUEUE_SIZE_MAX];   /**< Timer internal elapsed ticks queue. */
static uint8_t                       m_ticks_elapsed_q_read_ind;                /**< Timer internal elapsed ticks queue read index. */
static uint8_t                       m_ticks_elapsed_q_write_ind;               /**< Timer internal elapsed ticks queue write index. */
static bool                          m_rtc1_running;                            /**< Boolean indicating if RTC1 is running. */
static bool                          m_rtc1_reset;                              /**< Boolean indicating if RTC1 counter has been reset due to last timer removed from timer list during the timer list handling. */

#if APP_TIMER_WITH_PROFILER
static uint8_t                       m_max_user_op_queue_utilization;           /**< Maximum observed timer user operations queue utilization. */
#endif

/**@brief Function for initializing the RTC1 counter.
 *
 * @param[in] prescaler   Value of the RTC1 PRESCALER register. Set to 0 for no prescaling.
 */
static void rtc1_init(uint32_t prescaler)
{
    NRF_RTC1->PRESCALER = prescaler;
    NVIC_SetPriority(RTC1_IRQn, RTC1_IRQ_PRI);
}


/**@brief Function for starting the RTC1 timer.
 */
static void rtc1_start(void)
{
    NRF_RTC1->EVTENSET = RTC_EVTEN_COMPARE0_Msk;
    NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE0_Msk;

    NVIC_ClearPendingIRQ(RTC1_IRQn);
    NVIC_EnableIRQ(RTC1_IRQn);

    NRF_RTC1->TASKS_START = 1;
    nrf_delay_us(MAX_RTC_TASKS_DELAY);

    m_rtc1_running = true;
}


/**@brief Function for stopping the RTC1 timer.
 */
static void rtc1_stop(void)
{
    NVIC_DisableIRQ(RTC1_IRQn);

    NRF_RTC1->EVTENCLR = RTC_EVTEN_COMPARE0_Msk;
    NRF_RTC1->INTENCLR = RTC_INTENSET_COMPARE0_Msk;

    NRF_RTC1->TASKS_STOP = 1;
    nrf_delay_us(MAX_RTC_TASKS_DELAY);

    NRF_RTC1->TASKS_CLEAR = 1;
    m_ticks_latest        = 0;
    nrf_delay_us(MAX_RTC_TASKS_DELAY);

    m_rtc1_running = false;
}


/**@brief Function for returning the current value of the RTC1 counter.
 *
 * @return     Current value of the RTC1 counter.
 */
static __INLINE uint32_t rtc1_counter_get(void)
{
    return NRF_RTC1->COUNTER;
}


/**@brief Function for computing the difference between two RTC1 counter values.
 *
 * @return     Number of ticks elapsed from ticks_old to ticks_now.
 */
static __INLINE uint32_t ticks_diff_get(uint32_t ticks_now, uint32_t ticks_old)
{
    return ((ticks_now - ticks_old) & MAX_RTC_COUNTER_VAL);
}


/**@brief Function for setting the RTC1 Capture Compare register 0, and enabling the corresponding
 *        event.
 *
 * @param[in] value   New value of Capture Compare register 0.
 */
static __INLINE void rtc1_compare0_set(uint32_t value)
{
    NRF_RTC1->CC[0] = value;
}


/**@brief Function for inserting a timer in the timer list.
 *
 * @param[in]  timer_id   Id of timer to insert.
 */
static void timer_list_insert(timer_node_t * p_timer)
{
    if (mp_timer_id_head == NULL)
    {
        mp_timer_id_head = p_timer;
    }
    else
    {
        if (p_timer->ticks_to_expire <= mp_timer_id_head->ticks_to_expire)
        {
            mp_timer_id_head->ticks_to_expire -= p_timer->ticks_to_expire;

            p_timer->next   = mp_timer_id_head;
            mp_timer_id_head = p_timer;
        }
        else
        {
            timer_node_t * p_previous;
            timer_node_t * p_current;
            uint32_t       ticks_to_expire;

            ticks_to_expire   = p_timer->ticks_to_expire;
            p_previous        = mp_timer_id_head;
            p_current         = mp_timer_id_head;

            while ((p_current != NULL) && (ticks_to_expire > p_current->ticks_to_expire))
            {
                ticks_to_expire   -= p_current->ticks_to_expire;
                p_previous         = p_current;
                p_current          = p_current->next;
            }

            if (p_current != NULL)
            {
                p_current->ticks_to_expire -= ticks_to_expire;
            }

            p_timer->ticks_to_expire = ticks_to_expire;
            p_timer->next            = p_current;
            p_previous->next         = p_timer;
        }
    }
}


/**@brief Function for removing a timer from the timer queue.
 *
 * @param[in]  timer_id   Id of timer to remove.
 *
 * @return     TRUE if Capture Compare register must be updated, FALSE otherwise.
 */
static bool timer_list_remove(timer_node_t * p_timer)
{
    timer_node_t * p_old_head;
    timer_node_t * p_previous;
    timer_node_t * p_current;
    uint32_t       timeout;

    // Find the timer's position in timer list.
    p_old_head = mp_timer_id_head;
    p_previous = mp_timer_id_head;
    p_current  = p_previous;

    while (p_current != NULL)
    {
        if (p_current == p_timer)
        {
            break;
        }
        p_previous = p_current;
        p_current  = p_current->next;
    }

    // Timer not in active list.
    if (p_current == NULL)
    {
        return false;
    }

    // Timer is the first in the list
    if (p_previous == p_current)
    {
        mp_timer_id_head = mp_timer_id_head->next;

        // No more timers in the list. Reset RTC1 in case Start timer operations are present in the queue.
        if (mp_timer_id_head == NULL)
        {
            NRF_RTC1->TASKS_CLEAR = 1;
            m_ticks_latest        = 0;
            m_rtc1_reset          = true;
            nrf_delay_us(MAX_RTC_TASKS_DELAY);
        }
    }

    // Remaining timeout between next timeout.
    timeout = p_current->ticks_to_expire;

    // Link previous timer with next of this timer, i.e. removing the timer from list.
    p_previous->next = p_current->next;

    // If this is not the last timer, increment the next timer by this timer timeout.
    p_current = p_previous->next;
    if (p_current != NULL)
    {
        p_current->ticks_to_expire += timeout;
    }

    return (p_old_head != mp_timer_id_head);
}


/**@brief Function for scheduling a check for timeouts by generating a RTC1 interrupt.
 */
static void timer_timeouts_check_sched(void)
{
    NVIC_SetPendingIRQ(RTC1_IRQn);
}


/**@brief Function for scheduling a timer list update by generating a SWI interrupt.
 */
static void timer_list_handler_sched(void)
{
    NVIC_SetPendingIRQ(SWI_IRQn);
}

#if APP_TIMER_CONFIG_USE_SCHEDULER
static void timeout_handler_scheduled_exec(void * p_event_data, uint16_t event_size)
{
    APP_ERROR_CHECK_BOOL(event_size == sizeof(app_timer_event_t));
    app_timer_event_t const * p_timer_event = (app_timer_event_t *)p_event_data;

    p_timer_event->timeout_handler(p_timer_event->p_context);
}
#endif

/**@brief Function for executing an application timeout handler, either by calling it directly, or
 *        by passing an event to the @ref app_scheduler.
 *
 * @param[in]  p_timer   Pointer to expired timer.
 */
static void timeout_handler_exec(timer_node_t * p_timer)
{
#if APP_TIMER_CONFIG_USE_SCHEDULER
    app_timer_event_t timer_event;

    timer_event.timeout_handler = p_timer->p_timeout_handler;
    timer_event.p_context       = p_timer->p_context;
    uint32_t err_code = app_sched_event_put(&timer_event, sizeof(timer_event), timeout_handler_scheduled_exec);
    APP_ERROR_CHECK(err_code);
#else
    p_timer->p_timeout_handler(p_timer->p_context);
#endif
}


/**@brief Function for checking for expired timers.
 */
static void timer_timeouts_check(void)
{
    // Handle expired of timer
    if (mp_timer_id_head != NULL)
    {
        timer_node_t *  p_timer;
        timer_node_t *  p_previous_timer;
        uint32_t        ticks_elapsed;
        uint32_t        ticks_expired;

        // Initialize actual elapsed ticks being consumed to 0.
        ticks_expired = 0;

        // ticks_elapsed is collected here, job will use it.
        ticks_elapsed = ticks_diff_get(rtc1_counter_get(), m_ticks_latest);

        // Auto variable containing the head of timers expiring.
        p_timer = mp_timer_id_head;

        // Expire all timers within ticks_elapsed and collect ticks_expired.
        while (p_timer != NULL)
        {
            // Do nothing if timer did not expire.
            if (ticks_elapsed < p_timer->ticks_to_expire)
            {
                break;
            }

            // Decrement ticks_elapsed and collect expired ticks.
            ticks_elapsed -= p_timer->ticks_to_expire;
            ticks_expired += p_timer->ticks_to_expire;

            // Move to next timer.
            p_previous_timer = p_timer;
            p_timer = p_timer->next;

            // Execute Task.
            if (p_previous_timer->is_running)
            {
                p_previous_timer->is_running = false;
                timeout_handler_exec(p_previous_timer);
            }
        }

        // Prepare to queue the ticks expired in the m_ticks_elapsed queue.
        if (m_ticks_elapsed_q_read_ind == m_ticks_elapsed_q_write_ind)
        {
            // The read index of the queue is equal to the write index. This means the new
            // value of ticks_expired should be stored at a new location in the m_ticks_elapsed
            // queue (which is implemented as a double buffer).

            // Check if there will be a queue overflow.
            if (++m_ticks_elapsed_q_write_ind == CONTEXT_QUEUE_SIZE_MAX)
            {
                // There will be a queue overflow. Hence the write index should point to the start
                // of the queue.
                m_ticks_elapsed_q_write_ind = 0;
            }
        }

        // Queue the ticks expired.
        m_ticks_elapsed[m_ticks_elapsed_q_write_ind] = ticks_expired;

        timer_list_handler_sched();
    }
}


/**@brief Function for acquiring the number of ticks elapsed.
 *
 * @param[out] p_ticks_elapsed   Number of ticks elapsed.
 *
 * @return     TRUE if elapsed ticks was read from queue, FALSE otherwise.
 */
static bool elapsed_ticks_acquire(uint32_t * p_ticks_elapsed)
{
    // Pick the elapsed value from queue.
    if (m_ticks_elapsed_q_read_ind != m_ticks_elapsed_q_write_ind)
    {
        // Dequeue elapsed value.
        m_ticks_elapsed_q_read_ind++;
        if (m_ticks_elapsed_q_read_ind == CONTEXT_QUEUE_SIZE_MAX)
        {
            m_ticks_elapsed_q_read_ind = 0;
        }

        *p_ticks_elapsed = m_ticks_elapsed[m_ticks_elapsed_q_read_ind];

        m_ticks_latest += *p_ticks_elapsed;
        m_ticks_latest &= MAX_RTC_COUNTER_VAL;

        return true;
    }
    else
    {
        // No elapsed value in queue.
        *p_ticks_elapsed = 0;
        return false;
    }
}


/**@brief Function for updating the timer list for expired timers.
 *
 * @param[in]  ticks_elapsed         Number of elapsed ticks.
 * @param[in]  ticks_previous        Previous known value of the RTC counter.
 * @param[out] p_restart_list_head   List of repeating timers to be restarted.
 */
static void expired_timers_handler(uint32_t         ticks_elapsed,
                                   uint32_t         ticks_previous,
                                   timer_node_t **  p_restart_list_head)
{
    uint32_t ticks_expired = 0;

    while (mp_timer_id_head != NULL)
    {
        timer_node_t * p_timer;
        timer_node_t * p_timer_expired;

        // Auto variable for current timer node.
        p_timer = mp_timer_id_head;

        // Do nothing if timer did not expire
        if (ticks_elapsed < p_timer->ticks_to_expire)
        {
            p_timer->ticks_to_expire -= ticks_elapsed;
            break;
        }

        // Decrement ticks_elapsed and collect expired ticks.
        ticks_elapsed -= p_timer->ticks_to_expire;
        ticks_expired += p_timer->ticks_to_expire;

        // Timer expired, set ticks_to_expire zero.
        p_timer->ticks_to_expire = 0;

        // Remove the expired timer from head.
        p_timer_expired  = mp_timer_id_head;
        mp_timer_id_head = p_timer->next;

        // Timer will be restarted if periodic.
        if (p_timer->ticks_periodic_interval != 0)
        {
            p_timer->ticks_at_start       = (ticks_previous + ticks_expired) & MAX_RTC_COUNTER_VAL;
            p_timer->ticks_first_interval = p_timer->ticks_periodic_interval;
            p_timer->next                 = *p_restart_list_head;
            *p_restart_list_head          = p_timer_expired;
        }
    }
}


/**@brief Function for handling timer list insertions.
 *
 * @param[in]  p_restart_list_head   List of repeating timers to be restarted.
 *
 * @return     TRUE if Capture Compare register must be updated, FALSE otherwise.
 */
static bool list_insertions_handler(timer_node_t * p_restart_list_head)
{
    bool compare_update = false;

    timer_node_t * p_timer_id_old_head;

    // Remember the old head, so as to decide if new compare needs to be set.
    p_timer_id_old_head = mp_timer_id_head;

    // Handle insertions of timers.
    while ((p_restart_list_head != NULL) || (m_op_queue.first != m_op_queue.last))
    {
        timer_node_t * p_timer;

        if (p_restart_list_head != NULL)
        {
            p_timer           = p_restart_list_head;
            p_restart_list_head = p_timer->next;
        }
        else
        {
            timer_user_op_t * p_user_op = &m_op_queue.user_op_queue[m_op_queue.first];

            m_op_queue.first++;
            if (m_op_queue.first == m_op_queue.size)
            {
                m_op_queue.first = 0;
            }

            p_timer = p_user_op->p_node;

            switch (p_user_op->op_type)
            {
                case TIMER_USER_OP_TYPE_STOP:
                    // Delete node if timer is running.
                    if (timer_list_remove(p_user_op->p_node))
                    {
                        compare_update = true;
                    }

                    p_timer->is_running = false;
                    continue;

                case TIMER_USER_OP_TYPE_STOP_ALL:
                    // Delete list of running timers, and mark all timers as not running.
                    while (mp_timer_id_head != NULL)
                    {
                        timer_node_t * p_head = mp_timer_id_head;

                        p_head->is_running = false;
                        mp_timer_id_head    = p_head->next;
                    }
                    continue;
                case TIMER_USER_OP_TYPE_START:
                    break;
                default:
                    // No implementation needed.
                    continue;
            }

            if (p_timer->is_running)
            {
                continue;
            }

            p_timer->ticks_at_start          = p_user_op->params.start.ticks_at_start;
            p_timer->ticks_first_interval    = p_user_op->params.start.ticks_first_interval;
            p_timer->ticks_periodic_interval = p_user_op->params.start.ticks_periodic_interval;
            p_timer->p_context               = p_user_op->params.start.p_context;

            if (m_rtc1_reset)
            {
                p_timer->ticks_at_start = 0;
            }
        }

        // Prepare the node to be inserted.
        if (
             ((p_timer->ticks_at_start - m_ticks_latest) & MAX_RTC_COUNTER_VAL)
             <
             (MAX_RTC_COUNTER_VAL / 2)
            )
        {
            p_timer->ticks_to_expire = ticks_diff_get(p_timer->ticks_at_start, m_ticks_latest) +
                                       p_timer->ticks_first_interval;
        }
        else
        {
            uint32_t delta_current_start;

            delta_current_start = ticks_diff_get(m_ticks_latest, p_timer->ticks_at_start);
            if (p_timer->ticks_first_interval > delta_current_start)
            {
                p_timer->ticks_to_expire = p_timer->ticks_first_interval - delta_current_start;
            }
            else
            {
                p_timer->ticks_to_expire = 0;
            }
        }

        p_timer->ticks_at_start       = 0;
        p_timer->ticks_first_interval = 0;
        p_timer->is_running           = true;
        p_timer->next                 = NULL;

        // Insert into list
        timer_list_insert(p_timer);
    }

    return (compare_update || (mp_timer_id_head != p_timer_id_old_head));
}


/**@brief Function for updating the Capture Compare register.
 */
static void compare_reg_update(timer_node_t * p_timer_id_head_old)
{
    // Setup the timeout for timers on the head of the list
    if (mp_timer_id_head != NULL)
    {
        uint32_t ticks_to_expire = mp_timer_id_head->ticks_to_expire;
        uint32_t pre_counter_val = rtc1_counter_get();
        uint32_t cc              = m_ticks_latest;
        uint32_t ticks_elapsed   = ticks_diff_get(pre_counter_val, cc) + RTC_COMPARE_OFFSET_MIN;

        if (!m_rtc1_running)
        {
            // No timers were already running, start RTC
            rtc1_start();
        }

        cc += (ticks_elapsed < ticks_to_expire) ? ticks_to_expire : ticks_elapsed;
        cc &= MAX_RTC_COUNTER_VAL;

        rtc1_compare0_set(cc);

        uint32_t post_counter_val = rtc1_counter_get();

        if (
            (ticks_diff_get(post_counter_val, pre_counter_val) + RTC_COMPARE_OFFSET_MIN)
            >
            ticks_diff_get(cc, pre_counter_val)
           )
        {
            // When this happens the COMPARE event may not be triggered by the RTC.
            // The nRF51 Series User Specification states that if the COUNTER value is N
            // (i.e post_counter_val = N), writing N or N + 1 to a CC register may not trigger a
            // COMPARE event. Hence the RTC interrupt is forcefully pended by calling the following
            // function.
            rtc1_compare0_set(rtc1_counter_get());  // this should prevent CC to fire again in the background while the code is in RTC-ISR
            nrf_delay_us(MAX_RTC_TASKS_DELAY);
            timer_timeouts_check_sched();
        }
    }
    else
    {
#if (APP_TIMER_KEEPS_RTC_ACTIVE == 0)
        // No timers are running, stop RTC
        rtc1_stop();
#endif //(APP_TIMER_KEEPS_RTC_ACTIVE == 0)
    }
}


/**@brief Function for handling changes to the timer list.
 */
static void timer_list_handler(void)
{
    timer_node_t * p_restart_list_head = NULL;

    uint32_t       ticks_elapsed;
    uint32_t       ticks_previous;
    bool           ticks_have_elapsed;
    bool           compare_update = false;
    timer_node_t * p_timer_id_head_old;

#if APP_TIMER_WITH_PROFILER
    {
        uint8_t size = m_op_queue.size;
        uint8_t first = m_op_queue.first;
        uint8_t last = m_op_queue.last;
        uint8_t utilization = (first <= last) ? (last - first) : (size + 1 - first + last);

        if (utilization > m_max_user_op_queue_utilization)
        {
            m_max_user_op_queue_utilization = utilization;
        }
    }
#endif

    // Back up the previous known tick and previous list head
    ticks_previous    = m_ticks_latest;
    p_timer_id_head_old = mp_timer_id_head;

    // Get number of elapsed ticks
    ticks_have_elapsed = elapsed_ticks_acquire(&ticks_elapsed);

    // Handle expired timers
    if (ticks_have_elapsed)
    {
        expired_timers_handler(ticks_elapsed, ticks_previous, &p_restart_list_head);
        compare_update = true;
    }


    // Handle list insertions
    if (list_insertions_handler(p_restart_list_head))
    {
        compare_update = true;
    }

    // Update compare register if necessary
    if (compare_update)
    {
        compare_reg_update(p_timer_id_head_old);
    }
    m_rtc1_reset = false;
}


/**@brief Function for enqueueing a new operations queue entry.
 *
 * @param[in]  last_index Index of the next last index to be enqueued.
 */
static void user_op_enque(uint8_t last_index)
{
    m_op_queue.last = last_index;
}


/**@brief Function for allocating a new operations queue entry.
 *
 * @param[out] p_last_index Index of the next last index to be enqueued.
 *
 * @return     Pointer to allocated queue entry, or NULL if queue is full.
 */
static timer_user_op_t * user_op_alloc( uint8_t * p_last_index)
{
    uint8_t           last;
    timer_user_op_t * p_user_op;

    last = m_op_queue.last + 1;
    if (last == m_op_queue.size)
    {
        // Overflow case.
        last = 0;
    }
    if (last == m_op_queue.first)
    {
        // Queue is full.
        return NULL;
    }

    *p_last_index = last;
    p_user_op     = &m_op_queue.user_op_queue[m_op_queue.last];

    return p_user_op;
}


/**@brief Function for scheduling a Timer Start operation.
 *
 * @param[in]  timer_id          Id of timer to start.
 * @param[in]  timeout_initial   Time (in ticks) to first timer expiry.
 * @param[in]  timeout_periodic  Time (in ticks) between periodic expiries.
 * @param[in]  p_context         General purpose pointer. Will be passed to the timeout handler when
 *                               the timer expires.
 * @return     NRF_SUCCESS on success, otherwise an error code.
 */

static uint32_t timer_start_op_schedule(timer_node_t * p_node,
                                        uint32_t        timeout_initial,
                                        uint32_t        timeout_periodic,
                                        void *          p_context)
{
    uint8_t last_index;
    uint32_t err_code = NRF_SUCCESS;

    CRITICAL_REGION_ENTER();
    timer_user_op_t * p_user_op = user_op_alloc(&last_index);
    if (p_user_op == NULL)
    {
        err_code = NRF_ERROR_NO_MEM;
    }
    else
    {
        p_user_op->op_type                              = TIMER_USER_OP_TYPE_START;
        p_user_op->p_node                               = p_node;
        p_user_op->params.start.ticks_at_start          = rtc1_counter_get();
        p_user_op->params.start.ticks_first_interval    = timeout_initial;
        p_user_op->params.start.ticks_periodic_interval = timeout_periodic;
        p_user_op->params.start.p_context               = p_context;

        user_op_enque(last_index);
    }
    CRITICAL_REGION_EXIT();

    if (err_code == NRF_SUCCESS)
    {
        timer_list_handler_sched();
    }

    return err_code;
}


/**@brief Function for scheduling a Timer Stop operation.
 *
 * @param[in]  timer_id   Id of timer to stop.
 * @param[in]  op_type    Type of stop operation
 *
 * @return NRF_SUCCESS on successful scheduling a timer stop operation. NRF_ERROR_NO_MEM when there
 *         is no memory left to schedule the timer stop operation.
 */
static uint32_t timer_stop_op_schedule(timer_node_t * p_node,
                                       timer_user_op_type_t op_type)
{
    uint8_t last_index;
    uint32_t err_code = NRF_SUCCESS;

    CRITICAL_REGION_ENTER();
    timer_user_op_t * p_user_op = user_op_alloc(&last_index);
    if (p_user_op == NULL)
    {
        err_code = NRF_ERROR_NO_MEM;
    }
    else
    {
        p_user_op->op_type  = op_type;
        p_user_op->p_node = p_node;

        user_op_enque(last_index);
    }
    CRITICAL_REGION_EXIT();

    if (err_code == NRF_SUCCESS)
    {
        timer_list_handler_sched();
    }

    return err_code;
}

/**@brief Function for handling the RTC1 interrupt.
 *
 * @details Checks for timeouts, and executes timeout handlers for expired timers.
 */
void RTC1_IRQHandler(void)
{
    // Clear all events (also unexpected ones)
    NRF_RTC1->EVENTS_COMPARE[0] = 0;
    NRF_RTC1->EVENTS_COMPARE[1] = 0;
    NRF_RTC1->EVENTS_COMPARE[2] = 0;
    NRF_RTC1->EVENTS_COMPARE[3] = 0;
    NRF_RTC1->EVENTS_TICK       = 0;
    NRF_RTC1->EVENTS_OVRFLW     = 0;

    // Check for expired timers
    timer_timeouts_check();
}


/**@brief Function for handling the SWI interrupt.
 *
 * @details Performs all updates to the timer list.
 */
void SWI_IRQHandler(void)
{
    timer_list_handler();
}


ret_code_t app_timer_init(void)
{
    // Stop RTC to prevent any running timers from expiring (in case of reinitialization)
    rtc1_stop();

    // Initialize operation queue
    m_op_queue.first           = 0;
    m_op_queue.last            = 0;
    m_op_queue.size            = APP_TIMER_CONFIG_OP_QUEUE_SIZE+1;

    mp_timer_id_head            = NULL;
    m_ticks_elapsed_q_read_ind  = 0;
    m_ticks_elapsed_q_write_ind = 0;

#if APP_TIMER_WITH_PROFILER
    m_max_user_op_queue_utilization   = 0;
#endif

    NVIC_ClearPendingIRQ(SWI_IRQn);
    NVIC_SetPriority(SWI_IRQn, SWI_IRQ_PRI);
    NVIC_EnableIRQ(SWI_IRQn);

    rtc1_init(APP_TIMER_CONFIG_RTC_FREQUENCY);

    m_ticks_latest = rtc1_counter_get();

    return NRF_SUCCESS;
}


ret_code_t app_timer_create(app_timer_id_t const *      p_timer_id,
                            app_timer_mode_t            mode,
                            app_timer_timeout_handler_t timeout_handler)
{
    // Check state and parameters
    VERIFY_MODULE_INITIALIZED();

    if (timeout_handler == NULL)
    {
        return NRF_ERROR_INVALID_PARAM;
    }
    if (p_timer_id == NULL)
    {
        return NRF_ERROR_INVALID_PARAM;
    }
    if (((timer_node_t*)*p_timer_id)->is_running)
    {
        return NRF_ERROR_INVALID_STATE;
    }

    timer_node_t * p_node     = (timer_node_t *)*p_timer_id;
    p_node->is_running        = false;
    p_node->mode              = mode;
    p_node->p_timeout_handler = timeout_handler;
    return NRF_SUCCESS;
}

ret_code_t app_timer_start(app_timer_id_t timer_id, uint32_t timeout_ticks, void * p_context)
{
    uint32_t timeout_periodic;
    timer_node_t * p_node = (timer_node_t*)timer_id;

    // Check state and parameters
    VERIFY_MODULE_INITIALIZED();

    if (timer_id == 0)
    {
        return NRF_ERROR_INVALID_STATE;
    }
    if (timeout_ticks < APP_TIMER_MIN_TIMEOUT_TICKS)
    {
        return NRF_ERROR_INVALID_PARAM;
    }
    if (p_node->p_timeout_handler == NULL)
    {
        return NRF_ERROR_INVALID_STATE;
    }

    // Schedule timer start operation
    timeout_periodic = (p_node->mode == APP_TIMER_MODE_REPEATED) ? timeout_ticks : 0;

    return timer_start_op_schedule(p_node,
                                   timeout_ticks,
                                   timeout_periodic,
                                   p_context);
}


ret_code_t app_timer_stop(app_timer_id_t timer_id)
{
    timer_node_t * p_node = (timer_node_t*)timer_id;
    // Check state and parameters
    VERIFY_MODULE_INITIALIZED();

    if ((timer_id == NULL) || (p_node->p_timeout_handler == NULL))
    {
        return NRF_ERROR_INVALID_STATE;
    }

    p_node->is_running = false;

    // Schedule timer stop operation
    return timer_stop_op_schedule(p_node, TIMER_USER_OP_TYPE_STOP);
}


ret_code_t app_timer_stop_all(void)
{
    // Check state
    VERIFY_MODULE_INITIALIZED();

    return timer_stop_op_schedule(NULL, TIMER_USER_OP_TYPE_STOP_ALL);
}


uint32_t app_timer_cnt_get(void)
{ 
      
    return rtc1_counter_get();
}


uint32_t app_timer_cnt_diff_compute(uint32_t   ticks_to,
                                    uint32_t   ticks_from)
{
    return ticks_diff_get(ticks_to, ticks_from);
}

#if APP_TIMER_WITH_PROFILER
uint8_t app_timer_op_queue_utilization_get(void)
{
    return m_max_user_op_queue_utilization;
}
#endif

void app_timer_pause(void)
{
    NRF_RTC1->TASKS_STOP = 1;
}

void app_timer_resume(void)
{
    NRF_RTC1->TASKS_START = 1;
}

#endif //NRF_MODULE_ENABLED(APP_TIMER)

[Edvin]

I don't need to reproduce, but it is easier to navigate in your project to see what you are doing if I have the project. Your APP_TIMER_CONFIG_RTX_FREQUENCY is 0, meaning your app_timer is running on 32768Hz. 

Where do you set your prescaler to 15?

[Rajat]

Fullscreen timer_interra.c Download

/** @file timer_interra.c
*
* @brief A Timer used to generate the delay functionality, will later try to execute events.
*
* @par
* NOTICE: Property of in-Terra Limited www.in-terra.ch .
*/


#include "timer_interra.h"

APP_TIMER_DEF(m_led_0_timer_id);

uint8_t timer_exp_flag=0;

void timer_0_handler(void * p_context)
{ 
    timer_exp_flag=1; 
    
       
}


/*!
 * @brief Delay using the app timer
 *
 * @param[in] None
 *
 * @return    None
 */

uint8_t delay()
{

    if (timer_exp_flag == 1)
        {
            timer_exp_flag = 0;

            return 1;
        }
    else
        {   
            return 0;
        }
}


/*!
 * @brief Delay using the app timer
 *
 * @param[in] None
 *
 * @return    None
 */

uint8_t timer_ms(uint32_t time_miliseconds)
{

uint32_t err_code;
 
    err_code = app_timer_create(&m_led_0_timer_id,
                                APP_TIMER_MODE_SINGLE_SHOT,
                                timer_0_handler);
    APP_ERROR_CHECK(err_code);

    // Start timers
    err_code =app_timer_start(m_led_0_timer_id, APP_TIMER_TICKS(time_miliseconds), NULL);
    APP_ERROR_CHECK(err_code);
    
  while(delay()!=1);

 // while(timer_exp_flag!=1);
}




/*!
 * @brief Initilaize the Timer
 *
 * @param[in] None
 *
 * @return    None
 */

void
timer_init (void)
{
    
ret_code_t err_code;
err_code=app_timer_init();

 SEGGER_RTT_printf(0,"Error Code is %ld\r\n", err_code);      
   
}

/*!
 * @brief start the Timer
 *
 * @param[in] milsecond to expire
 *
 * @return    None
 */

void
timer_start(uint32_t ms_time)
{
    

        
   
}

timer_interra.h

[Rajat]

Inside timer_interra.h , i have defined

#define APP_TIMER_PRESCALER             15