APP_TIMER_DEF for several timers with same timer id. like C++ class member

[yacine]

hello

yes I have problems with my app_timers in SDK14.2 (migration from 12),

I well noticed that the prototypes of the functions create and start changed from sdk12.

// create timer

static app_timer_t timer_data = { {0} };

m_timer_id = &timer_data;

err_code = app_timer_create(&m_timer_id, APP_TIMER_MODE_REPEATED, cbk_measure);

APP_ERROR_CHECK(err_code);

-> this works well

ret_code_t err_code;

err_code = app_timer_start(m_timer_id, APP_TIMER_TICKS(m_probing_interval_ms), (void *) this);

NRF_LOG_DEBUG("FIXME: app_timer_start returns %d", err_code);

// APP_ERROR_CHECK(err_code);

-> but the start returns error code 8 (invalid param if i remember correctly) and I dont understand why. I tried APP_TIMER_DEF, but my timer_ids are C++ class members. I cannot simply use the APP_TIMER_DEF macro because I dont know if it ok if already declared. but it was already the case ion SDK12 and worked AFAIK

thx,

yacine

[Philip Odom]

The APP_TIMER_DEF macro instantiates an app_timer_id_t with the name you provide and another variable of type app_timer_t with the name appended with _data. app_timer_id_t is just a pointer to the app_timer_t (app_timer_t *).

For example:

APP_TIMER_DEF(my_timer);

expands to

static app_timer_t my_timer_data = { {0} };
static const app_timer_id_t my_timer = &my_timer_data;

So far so good, unless you want an app_timer to be a member of a struct or class, which is the problem I also ran into quickly. In that case, just do the same thing as the macro would, manually, and in your initialization code or constructor, set the app_timer_id_t member to the address of the timer.

In C++:

#include <cstdint>

using std::uint32_t;

class my_timer_class {
    public:
    my_timer_class()
    : timer(&timer_data)
    , timer_data()
    {
        app_timer_create(&timer, APP_TIMER_MODE_REPEATED, timer_handler_s);
    }
    
    virtual ~my_timer_class()
    {
    }
    
    void start_timer(const uint32_t ms)
    {
        app_timer_start(timer, APP_TIMER_TICKS(ms), this);
    }
    
    private:
    app_timer_id_t timer;
    app_timer_t timer_data;
    
    static void timer_handler_s(void *p_context)
    {
        ((my_timer_class*)p_context)->timer_handler();
    }
    
    void timer_handler()
    {
      //timer expired, do something!
    }
};

my_timer_class timer_object;

int main() {
  //start object's timer qith 1000 ms period
  timer_object.start_timer(1000);
}

In C, you either have to do the initialization at the time of instantiation or not make the app_timer_id_t const:

#include <stdio.h>
#include <stdint.h>

typedef struct struct_with_timer_s {
  const app_timer_id_t timer;
  app_timer_t timer_data;
} struct_with_timer_t;

//initialize timer_id (const) when declaring struct
struct_with_timer_t struct_with_timer = {.timer = &struct_with_timer.timer_data};

void struct_with_timer_handler(struct_with_timer_t *const this)
{
  //timer expired, do something!
  printf("tick\n");
}

void struct_with_timer_static_handler(void * p_context)
{
  struct_with_timer_handler((struct_with_timer_t *)p_context);
}

void struct_with_timer_init(struct_with_timer_t *const this)
{
  uint32_t error_code = app_timer_create(&this->timer, APP_TIMER_MODE_REPEATED, struct_with_timer_static_handler);
  APP_ERROR_CHECK(error_code);
}

void struct_with_timer_start(struct_with_timer_t *const this, const uint32_t ms)
{
  app_timer_start(this->timer, APP_TIMER_TICKS(ms), this);
}

int main(void) {
  //initialize struct
  struct_with_timer_init(&struct_with_timer);
  //start its timer with 1000 ms period
  struct_with_timer_start(&struct_with_timer, 1000);
  return 0;
}