Unpredictable behaviour of RTC2 on nRF24le1

[EwanX]

I found a problem using the RTC2 on the nRF24le1 which i dont know how to solve it.

I am using the RTC2 on the master to generate a TICK interrupt exactly every 1s. With the formula on page 97, i set the compare register RTC2CMP1:RTC2CMP1 to 7FFE which should generate interrupts exactly every 1s. But the behaviour is in two points different as expected.

1. The RTC2 generates interrupts 3-6 ms earlier, so the interval is like 0,996869s which corresponds to 7F98 and not 7FFE.

2. The interval decreases every second one RTC2 tick (like 7F97, 7F96, 7F95, ...). Is this a bug?

How can i solve this, especially the point 2.? I need a constant interval.

Regards

[EwanX]

Hi Torgjorn, sorry for my late reply.

My LF clock source is RCOSC32K because my module does not have an external 32k quarz. I does not find a upload button so i post the code here:

// nRF24LE1 SPI Master #include <nordic_common.h> #include "hal_nrf.h" #include "hal_clk.h" #include "hal_delay.h"

#define RTC2_TIMEOUT 32767 // 1s

// Global variables uint8_t rtccount = 0;

/****************************

• Interrupt service routines ****************************/ TICK_ISR() // interrupt INTERRUPT_TICK (Internal wakeup interrupt (0x6b)) { P04 = 0; // Set Low, for starting logic analyzer trigger rtccount = 255;

  //WUF = 0; // Cleared automatically }

/*************************************

• Functions *************************************/ void RTC2_init(uint16_t time) { //CLKCTRL = ?? CLKLFCTRL = 0x01; // RCOSC32K is used

  RTC2CON = 0x06; // Bit 2-1 (11): Compare mode: IRQ is set when equal. // When IRQ is assigned, Timer value is then reset RTC2CMP0 = (time & 0xFF); // Lowbyte of (value + 1 / 32768) (0x7FFF ~1s) RTC2CMP1 = (time >> 8) & 0xFF; // Highbyte }

void RTC2_start(void) { WUCON &= ~(BIT_4 | BIT_5); // 00: Enable wakeup on TICK if WUIRQ is enabled WUIRQ = 1; // Enable TICK Interrupt (IEN1.5)

RTC2CON |= BIT_0; // Bit 0: = 1: RTC2 is enabled }

void RTC2_stop(void) { RTC2CON &= ~BIT_0; // Bit 0: = 0: RTC2 is disabled

WUIRQ = 0; // Disable TICK Interrupt (IEN1.5) WUCON |= (BIT_4 | BIT_5); // 11: Ignore TICK (Bit 5-4) WUF = 0; // Clear interrupt }

void MCU_init(void) { // P0.4 used for Logic analyzer start P0DIR &= ~BIT_4; // Set pin P0.4 as output (used for trigger Start) P0CON = 0x04; // Activate P0.4 (Digital output buffer on, normal drive strength) P04 = 1; // Set to High, due to active low behaviour

RFCKEN = 1; // Enable the radio clock (RFCON.2) RF = 1; // Enable RF interrupt EA = 1; // Enable global interrupts }

/*************************************

• Main routine *************************************/ void main(void) { MCU_init(); // Initialize MCU

  RTC2_stop(); // Stop RTC2 timer (Clear bits) RTC2_init(RTC2_TIMEOUT); // Init RTC2 with default timeout 1s RTC2_start(); // Start RTC2

  while(1) { if(rtccount > 0) { --rtccount;

     if(rtccount == 0)
        P04 = 1;                            // Set to High, due to active low behaviour
  }
  

  } }