RTC Timer re-initialization

[TigerD]

Hi,

I have nRF52840 DK and am using nRF5_SDK_17.0.2_d674dde.

I am not using SoftDevice, and Zephyr RTOS.

I have a simple program and using RTC0 timer. My code snippet:

const uint32_t m_dwPreScales[10]={
4095,1365,819,585,455,  315,273,195,151,105};
const uint32_t m_dwRTCsCC[10]={
8, 24, 40, 56, 72,  104,120,168,216,312};

void rtc_initialize(void) {
    uint32_t err_code;
    k++;
    if (k>=9) k=0;
    //k=5;
    //=======================================================
    NRF_RTC0->TASKS_STOP= 1;
    NVIC_ClearPendingIRQ(RTC0_IRQn);
    NVIC_DisableIRQ(RTC0_IRQn);
    NRF_RTC0->EVTENCLR = RTC_INT_MASK;
    NRF_RTC0->INTENCLR = RTC_INT_MASK;
    //=======================================================
    volatile uint32_t prescaler= m_dwPreScales[k];
    volatile uint32_t duration_ticks= m_dwRTCsCC[k];
    NRF_RTC0->TASKS_CLEAR= 1;
    //NRF_RTC0->TASKS_TRIGOVRFLW= 1;
    NRF_RTC0->PRESCALER = prescaler;
    NRF_RTC0->CC[0]     = 3;
    NRF_RTC0->CC[1]     = duration_ticks;

    NRF_RTC0->INTENSET = RTC_CHANNEL_INT_MASK(0);
    NRF_RTC0->EVTENSET = RTC_CHANNEL_INT_MASK(0);
    NRF_RTC0->INTENSET = RTC_CHANNEL_INT_MASK(1);
    NRF_RTC0->EVTENSET = RTC_CHANNEL_INT_MASK(1);
    NRF_RTC0->EVTENSET = NRF_RTC_INT_TICK_MASK;
    NVIC_SetPriority(RTC0_IRQn, 2);  
    NVIC_EnableIRQ(RTC0_IRQn);
    NRF_RTC0->TASKS_START=1U;
    //======================================================
}
 
void RTC0_IRQHandler(void)
{
   if(NRF_RTC0->EVENTS_TICK){
       NRF_RTC0->EVENTS_TICK = 0;
   }
    
   if ((NRF_RTC0->EVENTS_COMPARE[0] != 0) )  
   {
      NRF_RTC0->EVENTS_COMPARE[0] = 0;  
      nrf_gpio_pin_toggle(LED1_PIN);
   }

   if ((NRF_RTC0->EVENTS_COMPARE[1] != 0))
   {
      NRF_RTC0->EVENTS_COMPARE[1] = 0;  
      nrf_gpio_pin_toggle(LED1_PIN);
      rtc_initialize();
      //NRF_RTC0->TASKS_START =1U;
   }
   if(NRF_RTC0->EVENTS_OVRFLW){
       NRF_RTC0->EVENTS_OVRFLW = 0;
   }  
   return ;
}

The code runs OK, the period is 1 second for any fixed k, which basically prescaler and CC[1]. Only CC[0] and CC[1] are enabled. For any fixed k with a pair of prescaler and CC1, with event period is 1 second.

But If I change k++, everytime re-initialization, the period becomes  1s, 2s, 3s,4s, 5s, ... (may not exactly).

Could you please help me take a code review for apparent mistakes?

Thank you,

David

[Dmitry]

Hi,

if I understood your question right - RTC is clocked from LFCLK and thus has up to 46 usec delay from writing to TASK register to actual task execution. Try to add nfr_delay_us(50) after stopping timer - this will ensure that PRESCALER is written when timer is stopped.

[TigerD]

Hi Dmitry,

Thank you for your help. I believe this is the case. I will test it out.

Best Regards,

David Zhou

[ovrebekk]

Hi David

I can't see any obvious mistake in the code, other than the fact that it is a bit unorthodox to reconfigure the entire peripheral and it's interrupt inside its own interrupt handler. 

What happens if you rather try just to clear the RTC timer when the EVENTS_COMPARE[1] interrupt happens, and only do a full re-initialize every 10 seconds or so (either by using a separate timer to schedule this, or by checking a counter inside the interrupt and wait for the counter to reach a certain value)?

Also, you could try just to run the rtc_initialize() function from main rather than interrupt context, by setting a flag in the interrupt handler that you can check from the main loop. 

Best regards
Torbjørn

[TigerD]

Hi Torbjorn

Thank you so much for your code review, explanation, and solutions for me.

I now realized that RTC in on LFCLK, it needs time to settle or for prescaler, etc. to take effective. I will resolve it my self based on my application.

Best Regards,

David

[ovrebekk]

Hi David

Sounds good. Unless you have more questions I will consider the case resolved then

Best regards
Torbjørn