Use p_event_data parameter of app_sched_event_put to pass just a uint32_t value to the handler parameter

Question

I'm using SDK17.1 and pca10056 DK board. I want to use app_sched_event_put for a very simple purpose. I start a one second clock whose timeout handler increments a static local uint32_t counter. The timeout handler then uses app_sched_event_put to transfer the uint32_t one second counter's value, not it's address, to the app_sched_event_put's handler. Unfortunately, the handler's void *p_event_data looks like an address even after doing a (uint32_t)p_event_data cast.

Code sample followed by some RTTViewer output.

static bool main_loop_started = false;

// Scheduler settings
#define SCHED_MAX_EVENT_DATA_SIZE   APP_TIMER_SCHED_EVENT_DATA_SIZE
#define SCHED_QUEUE_SIZE            16

APP_TIMER_DEF(m_our_app_timer_id);
#define TIMER_INTERVAL   APP_TIMER_TICKS(1000)   // every 1000 msecs


void timer_timeout_action(void *p_event_data, uint16_t event_size)
{
    uint32_t loop_count = (uint32_t)p_event_data;
    NRF_LOG_INFO("        timeout_action:  p_event_data = %d  loop_count = %d", p_event_data, loop_count);
}


static void timer_timeout_handler(void * p_context)
{
    static uint32_t loop_count = 0;

    ++loop_count;

    if (main_loop_started)
    {
        app_sched_event_put((void *)loop_count, 0, timer_timeout_action);
        NRF_LOG_INFO("timeout_handler: &loop_count = %d  loop_count = %d", &loop_count, loop_count);
    }
}


static void timers_init(void)
{
    ret_code_t err_code;

    // Make sure the LF clock is running
    err_code = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request(NULL);
    nrfx_clock_lfclk_start();

    // Initialize timer module
    err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);

    // Create timers
    err_code = app_timer_create(&m_our_app_timer_id, APP_TIMER_MODE_REPEATED, timer_timeout_handler);
    APP_ERROR_CHECK(err_code);
}


static void application_timers_start(void)
{
    ret_code_t err_code;
    err_code = app_timer_start(m_our_app_timer_id, TIMER_INTERVAL, NULL);
    APP_ERROR_CHECK(err_code);
}


static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(get_Nordic_rtc_counter);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}


static void power_management_init(void)
{
    ret_code_t err_code;
    err_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(err_code);
}


static void idle_state_handler(void)
{
    if (NRF_LOG_PROCESS() == false)
    {
        nrf_pwr_mgmt_run();
    }
}


int main(void)
{
    ret_code_t err_code;

    // Initialize
    APP_SCHED_INIT(SCHED_MAX_EVENT_DATA_SIZE, SCHED_QUEUE_SIZE);
    log_init();

    timers_init();

    application_timers_start();

    power_management_init();

    NRF_LOG_INFO("DevKit APP Schedular practice started.\n");

    // Enter main loop.
    main_loop_started = true;
    for (;;)
    {
        app_sched_execute();
        idle_state_handler();
    }
}

00> [00:00:43.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 43
00> [00:00:43.000,061] <info> app:         timeout_action:  p_event_data = 536874048  loop_count = 536874048
00> [00:00:44.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 44
00> [00:00:44.000,061] <info> app:         timeout_action:  p_event_data = 536874056  loop_count = 536874056
00> [00:00:45.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 45
00> [00:00:45.000,061] <info> app:         timeout_action:  p_event_data = 536874064  loop_count = 536874064
00> [00:00:46.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 46
00> [00:00:46.000,061] <info> app:         timeout_action:  p_event_data = 536874072  loop_count = 536874072
00> [00:00:47.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 47
00> [00:00:47.000,061] <info> app:         timeout_action:  p_event_data = 536874080  loop_count = 536874080
00> [00:00:48.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 48
00> [00:00:48.000,061] <info> app:         timeout_action:  p_event_data = 536874088  loop_count = 536874088
00> [00:00:49.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 49
00> [00:00:49.000,061] <info> app:         timeout_action:  p_event_data = 536874096  loop_count = 536874096
00> [00:00:50.000,000] <info> app: timeout_handler: &loop_count = 536873844  loop_count = 50
00> [00:00:50.000,061] <info> app:         timeout_action:  p_event_data = 536874104  loop_count = 536874104

As you can see from the RTTViewer output, the timer_timeout_action's void *p_event_data isn't loop_count's value.

Can I use the app_sched_event_put's p_event_data pointer's memory slot to hold a single uint32_t value and pass it as such to the handler?

I'm motivated to do this because if app_sched_execute starts a process that takes longer than a second, I could wind up with two events in the queue pointing to the same value, (the increment of the increment), instead of two different values, (the current increment and the previous increment).

I would like to add that providing a sizeof(uint32_t) as app_sched_event_put's 2nd parameter doesn't change the outcome.

Hung Bui · Accepted Answer

Hi Matty, 
 Yes, what you observed is correct. The app_scheduler take in to account that and do a copy of the content of the data point into its own buffer. (I also didn't know about this before) 
 So here is the code inside app_sched_event_put(), and you can see that the data is copied into the buffer using memcpy: 
 
 So, you don't really have to worry that the subsequence events may change the original data of the previous event if it's not executed fast enough.

Use p_event_data parameter of app_sched_event_put to pass just a uint32_t value to the handler parameter

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