Porting of RTC example code to ble_app_bliky

[beemavishnu]

Hello,

 

I am using nRF52832, SDK_15.3.0, S132 SoftDevice and Segger for flash the image. I am using ‘ble_app_blinky’.

I am porting RTC example code as is into ble_app_blinky. I have below queries.

 

1) When I use RTC0, code got crashed with below error on Terminal.

              const nrf_drv_rtc_t rtc = NRF_DRV_RTC_INSTANCE(0);

 

              <error> app: SOFTDEVICE: INVALID MEMORY ACCESS

 

              In SoftDevice manual its mentioned as RTC0 is blocked by SoftDevice. But as part of app_timer_init() I am seeing RTC1 being used. Whereas in document it is mentioned RTC1 as open. Whether both RTC0 & RTC1 are being used by SoftDevice.

 

Later I changed to RTC2 and it worked as expected.

const nrf_drv_rtc_t rtc = NRF_DRV_RTC_INSTANCE(2);

 

2) Even though SoftDevice uses RTC0, how will I come to know which CC[0..3] is used by RTC0, so that I can give other CC as part of RTC2 configuration.

3) Since I am using RTC2, in-between LED blink (Say 250ms) whether chip will go to low power mode ? Is it taken care automatically (By calling idle_state_handle()) or do need to add any extra code ?

             

4) In TIMER once timer is enabled COUNTER will keep on triggering, whereas in RTC its only once. After that there is not COUNTER interrupt in RTC. For this , in rtc_handler() do I need to clear COUNTER register and write CC once again. If I comment nrf_drv_rtc_cc_set() I am not seeing rtc_handler() event handler getting triggered.

 

              if (int_type == NRF_DRV_RTC_INT_COMPARE0) // For RTC2, CC0 is used

              {

        nrf_gpio_pin_toggle(LED_1);

        nrf_drv_rtc_counter_clear(&rtc);

        nrf_drv_rtc_cc_set(&rtc, 0, 32UL, true); // With 255 prescale (250ms)  // Is this really required ??

 

    Why is that in RTC whereas not in TIMER functionality and how to trigger rtc_handler() continuously.

Thanks & Regards

Vishnu Beema

[haakonsh]

1. RTC0 is used by the SoftDevice, RTC1 is used by the app_timer, RTC2 is free to use.
   
   
2. The CC registers are not shared across the RTCs, you can safely use all CC registers of RTC2.
3. You just need to call idle_state_handle() in your main loop. 
   
4. You do not need to set the CC register for each iteration of the RTC. I'm afraid I have a hard time understanding what your actual issue is.
   
   Btw, you do not need to use the CPU to toggle that pin, you can use GPIOTE — GPIO tasks and events and PPI — Programmable peripheral interconnect to achieve the same goal. 
   
   
   

[beemavishnu]

Hello,

I was referring to below link. In this CC of RTC to be cleared and need to set again. Please check and confirm.

https://devzone.nordicsemi.com/f/nordic-q-a/8772/rtc-nrf51-sdk-example-matches-compare0-only-once

Thanks & Regards

Vishnu Beema

[haakonsh]

It is the compare interrupt getting disabled in the RTC IRQ. The nrf_drv_rtc_cc_set function enabled the interrupt again, it has nothing to do with setting the CC register and everything to to with setting the interrupt.

So, in your RTC handler you need to enable the interrupt for the CC channel that was just fired with a call to nrfx_rtc_int_enable, otherwise the interrupt will remain disabled. 

If you need an accurate RTC then you need to clear the RTC via PPI instead of doing it in the RTC event handler. 


Again, I urge you to use GPIOTE and PPI, then you wont have to deal with any interrupts at all.