Can Softdevice RTC be used without an interrupt handler?

[kjhuebner]

I want to run the realtime counter RTC2 with softdevice S132 WITHOUT an interrupt handler.  I have no purpose for an RTC2 interrupt handler in my code, as I simply want to poll the hardware based RTC2 counter.  Also, since the RTC2 clock will be set at 8192 hz, I do not want an interrupt eating up cpu cycles and consuming extra electrical power.

Is this possible?

Hardware: Nordic nrf52832

Softdevice: S132

Currently the following source code gives me a softdevice error.

#define APP_RTC_CLOCK_FREQ       8192    //hz
#define APP_APPL_CLOCK_FREQ       32      //hz
    config.prescaler = 3;     //resulting freq= 8192 hz.
    err_code = nrf_drv_rtc_init(&m_rtc, &config, NULL);
    APP_ERROR_CHECK(err_code);

RTT Viewer shows this error:

00> <error> app: ERROR 3735928559 [Unknown error code] at C:\segger_ws\nRF5_SDK\modules\nrfx\drivers\src\nrfx_rtc.c:82

The error is occurring because there is a

NRFX_ASSERT(handler);

at the top of nrfx_rtc_init() within nrfx_rtc.c module.

Whereby, the current code does not allow a NULL handler.

ALTERNATIVE SOLUTIONS:

 1.  Customize Noridic's softdevice code inside the nrfx_rtc.c module.   OPINION - DUMB.  Makes codebase very complex.  Nordic should address this, not me.

 2.  Use a bare metal solution where I setup the RTC2 counter independent of the softdevice libarary functions.   OPINION - DUMB.  There may be conflicts between softdevice operations and my custom code. 

NRF_RTC1->TASKS_STOP  = 1;

delay_mS(0.1);

NRF_RTC1->TASKS_CLEAR = 1;

NRF_RTC1->PRESCALER   = 0;

   

NRF_RTC1->EVTEN = 0x000F0003;

NRF_RTC1->INTENCLR = 0;

NRF_RTC1->EVTENCLR = 0x000F0003;

 

NRF_RTC1->TASKS_START = 1;

delay_mS(0.1);

NO GOOD SOLUTIONS... SO WHERE DOES THIS LEAVE ME?

Ken Huebner

Software Engineer

Huebner Design

[kjhuebner]

If my memory serves me right -- I confirmed the RTC2 clock rate by creating a program loop that polls the RTC2 clock value and toggling an IO pin.  Then while the Nordic device is running, observing the IO pin using an oscilloscope.  

The pseudo code looks like this...

unsigned int read_value;

while(true)

{

  read_value= RTC2 clock value ;

  while (read_value == RTC2 clock value)

      ;

  set IO pin = high

  read_value= RTC2 clock value ;

  while (read_value == RTC2 clock value)

      ;

  set IO pin = low

}

Keep in mind for the above code...  your logic analyzer will show a

frequency rate= desired RTC2 clock rate divided by 2.

The reason is the above code has a toggle high and a toggle low for each full wave of output signal.  I think you get the picture.

ALTERNATIVE SOLUTION:

One could read RTC2 clock into "read_value", then add 1000 to read_value, then poll the RTC2 clock until it reaches the value, then toggle IO pin.  This would avoid the possibility of missing clock ticks if your RTC2 clock rate is exceptionally high.  Of course in this case, your oscilloscope or logic analyzer will show a

frequency rate= desired RTC2 clock rate divided by 2000.

-Ken