RTC1 Timer - Counter in IRQ handler

[Ck]

Hello,

I'm using: nRF51422-QFAA E00 and SDK - nRF51 5.2.0

Right now I'm running without softdevice enabled. I'm trying to use RTC1 Timer for my own delay_ms() function. I know you have app_timer and scheduler for that but I don't want to use it now.

My 1st question is about init of RTC1 with IRQ. I'm not using PPI at all so I don't need to have enabled EVENT, right? But in your examples before you set INTENSET you always set coresponding EVTENSET. Is it necessary in my case too? I don't want event for that, just jump to IRQ handler. As I tried it works even without EVTENSET line but I'm not sure if it's safe. My code for that is:

void V_hw_rtc_init(void)
{	
  NRF_RTC1->PRESCALER = RTC1_PRESCALER; 
  NRF_RTC1->CC[0] = RTC1_CC0;  
  NVIC_SetPriority(RTC1_IRQn, APP_IRQ_PRIORITY_LOW);
	
  //NRF_RTC1->EVTENSET = RTC_EVTEN_COMPARE0_Msk; 		// Event has to be enabled for IRQ generation?
  NRF_RTC1->INTENSET = RTC_INTENSET_COMPARE0_Msk;
	
  NVIC_ClearPendingIRQ(RTC1_IRQn);
  NVIC_EnableIRQ(RTC1_IRQn);
}

2nd question: Counter is incrementing during IRQ handler is proceed (at least uLINK2 debuger says). My CC[0] has value only 6. Even if update of CC[0] is last line at IRQ handler the counter will be bigger before it will quit IRQ handler, so Compare Event was not generated and my code stucked - was waiting to counter overflow. I tried even calling TASK_CLEAR but again counter increased much more than CC[0] before IRQ handler quit, but at least it set compare flag and IRQ was called again in this case.

void RTC1_IRQHandler(void)
{
  if (NRF_RTC1->EVENTS_COMPARE[0] != 0)
  {
    if(U32_delay_ms) U32_delay_ms--; // used in V_hw_delay_ms()
    NRF_RTC1->EVENTS_COMPARE[0] = 0;
    NRF_RTC1->TASKS_CLEAR = 1;  // Clear Counter
    //NRF_RTC1->CC[0] += RTC1_CC0;
  }

}

Is there some workaround different than setting lower prescaler and higher CC ?

[John]

I believe I can help you with your first question. You do not need to enable the EVENT to use an interrupt. I have several interrupts configured that way and they work just fine. If you want to convince yourself read section 10 of the reference manual a few times everything you need to know is there I think.

[Ck]

Thanks for reply. Well I have read chapter Peripheral interface, but I think there should be more detailed infos and examples. By Figure 5 it looks like EVENT has to be enabled to produce NVIC IRQ. Problem is I have not much time for my project to investigate how things works (Shorts, Scheduler etc.).

[John]

I can sympathize with you on the detail. I really like the nRF51822 and have enjoyed developing our product on it. Plus the Nordic support has been awesome. But there was a learning curve and you have to read the documentation carefully as there is a lot of information that isn't explicitly spelled out but it's there if you read closely enough.