Timer expires instantly

Question

Hi all, 
 I have seen a pair of questions ( this and this ) that I think have something to do with this, but didn't find a solution. 
 I have a custom board with a button which acts as a reset button. This button must be pressed during 3 seconds to reset the device (otherwise it has no effect). I do this activating a 3 seconds timer when the button is pressed, and when the timer expires, I reset the device. If I release the button before, I stop the timer. 
 Normally this goes well, but I have found that after waiting for some time (maybe 5 minutes), the next time I press the button, the reset occurs instantly (because the timer that should expire in 3 seconds does it instantly). I attach the relevant part of the code: 
 Buttons interrupt handler: 
 static void button_evt_handler(uint8_t pin_no, uint8_t button_action)
{	
	if (button_action == APP_BUTTON_PUSH && pin_no == PIN_RESET_BUTTON)
 {
 start_reset_button_timer();
 }else if(button_action == APP_BUTTON_RELEASE && pin_no == PIN_RESET_BUTTON)
	{
 stop_reset_button_timer();
	}
}
 
 Timer functions (I init the timer once at the beginning of the code): 
 static void reset_button_handler(void * p_context) // After 3 seconds pressing the button we get here
{
	// Factory values
	set_param_default_values(&param_ibk); // Set default values in flash and reset
	uint32_t err_code = access_paramIBK_flash(&param_ibk, ES_FLASH_ACCESS_WRITE);
	APP_ERROR_CHECK(err_code);
	
	// Reset after flash
	flag_reset=true;
}

void init_reset_button_timer(void)
{
	uint32_t err_code;
	
	err_code = app_timer_create(&reset_button_timer, APP_TIMER_MODE_SINGLE_SHOT, reset_button_handler);
	APP_ERROR_CHECK(err_code);
}

void start_reset_button_timer(void)
{
	uint32_t err_code;
	
	err_code = app_timer_start(reset_button_timer, APP_TIMER_TICKS(TIME_RESET_BUTTON, APP_TIMER_PRESCALER), NULL); // After 3 seconds will reset the device if not stopped before
	APP_ERROR_CHECK(err_code);
}

void stop_reset_button_timer(void)
{
	app_timer_stop(reset_button_timer); // Button released, timer stopped
}
 
 and TIME_RESET_BUTTON defined as 3000, and the flag_reset variable will reset the code properly after flash writing. 
 I am using the following: 
 nRF52832 
 SDK 12.2.0 
 Code based on experimental_ble_app_eddystone example. 
 Is there any solution to this, or maybe I am doing something wrong? 
 Thank you

dblasco · Accepted Answer

I have found that when no timer is executed within 256 seconds (with prescaler 0), when the next timer is executed it will be done immediately. This is the same as in this question . 
 To solve this I have created a dummy timer that does nothing but is executed repetadly at 256-1 seconds.

Timer expires instantly

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