RTC Zero losing time

[sbaratheon]

EDIT: This is very weird - I have swapped for another (virtually identical board) and the below issue does not present (i.e. the clock keeps counting). Is the board's RTC defective?

Hi

I have an Arduino Zero and I am using this library to keep a track of the time using the inbuilt 'rtc'. However, I have noticed that my rtc stops counting time when I call the sendText() function. The code below demonstrates the problem:

  #include <Arduino.h>

#include <RtcAlarmScheduler.h>
#include <RadioFunctions.h>

// clock object
RTCZero remoteStationClock;

// alarms and ISRs
#define CS_M0  8
#define RST_M0 4
#define INT_M0 3

// Radio settings
const int FREQ = 434;
const int TX_PWR = 20;
const int SPREAD_FACTOR = 12;
const int BANDWIDTH = 125E3; 
const int CODING_DENOM = 5;
const bool CRC_ON = true;

RH_RF95 remoteStationRadio(CS_M0, INT_M0);

char TEST_TXT[] = "HELLO TEST WORLD BLAH BLAH BLAH. GOODBYE!HELLO TEST WORLD BLAH BLAH BLAH. GOODBYE!HELLO TEST WORLD BLAH BLAH BLAH. GOODBYE!";

bool sendText(const char* txt, RH_RF95& radio)
{
   if ( !radio.send( (uint8_t*)txt, strlen(txt)) )
   {
     return false;
   }

  if ( !radio.waitPacketSent() )
   {
     return false;
   }
  radio.setModeRx(); // put back into RX mode
  return true;
}

void setup() {
    
    Serial.begin(9600);
    const int C_TIME = 1622494907;

    Serial.print("TIME IS: ");
    Serial.println(C_TIME);

    remoteStationClock.begin();
    remoteStationClock.setEpoch(C_TIME);

    setupRadio(remoteStationRadio,RST_M0, FREQ, TX_PWR, SPREAD_FACTOR, BANDWIDTH, CODING_DENOM, CRC_ON);
    Serial.println("RADIO SETUP");

}

void loop() {
   
    delay(10000);

    Serial.print("EPOCH START:");
    Serial.println(remoteStationClock.getEpoch());
    uint32_t startSW = millis();
    
     if ( !sendText(TEST_TXT, remoteStationRadio) )
     {
       Serial.println("FAILED TO SEND");
     }

    Serial.print("SEND TIME (MSECS):");
    Serial.println(millis() - startSW);
    Serial.print("EPOCH END:");
    Serial.println(remoteStationClock.getEpoch());
    Serial.println("");

}

This produces the following output:

EPOCH START:1622494917
SEND TIME (MSECS):4926
EPOCH END:1622494917 // why isn't this 1622494917 + 4.9 secs?

EPOCH START:1622494927
SEND TIME (MSECS):4926
EPOCH END:1622494928

EPOCH START:1622494938
SEND TIME (MSECS):4925
EPOCH END:1622494938

Does anyone know what might be going on here? Why does the clock stop during this function?

Thanks

[Juraj]

Arduino M0 and other SAMD boards with M0 bootloader loose RTC time at reset because the bootloader resets RTC.

[tigger]

Not a great RTC, then.
Good information.

[sbaratheon]

The board isn't being reset - at setup the time is set from an external source. During execution, it seems to lose time.