Alarms do not fire when time is changed

[kdhooper]

When changing the time in the Time library, TimeAlarms misses alarms.

The expected behavior is:

update() {
  if(last_update_time < alarm_time < present_update_time) {
    TriggerAlarmCallback();
  }
}

..in other words, every instance of the time passing through a recurring alarm should result in the alarm firing.

You can demonstrate this bug by

• Set the time for 7:00AM,
• Set a recurring alarm for 7:02AM
• Watch it trigger
• Set the time again to 7:00AM
• The alarm will not trigger the second time

A more practical example of this bug is if the time is set to 7:00PM and you run the clock back to 7:00AM, the alarm will not trigger. This is highly likely to cause alarms (possibly for the whole day) to be missed, and is something a user of an alarm clock might do.

Workaround:
Update the alarm each instance of updating the time:

void saveTimeCurrentTime(uint8_t setHour, uint8_t setMinute) {
  setTime(setHour, setMinute, 0, day(), month(), year());
  Alarm.write(gAlarmID1, AlarmHMS(gTime1.hours, gTime1.minutes, 0));
}

Where gTime1 struct holds the hour and minute of the alarm as a global variable.

[luckyhacky]

I have the same issue. Alarms are omited if NTPClient updated time.

[luckyhacky]

I found my problem. Just a short sketch for everybody using a similar code:

int ntp_time = 0;
NTPClient ...

void setup()
{
setSyncProvider(ntp_set_time);
...
}


void loop()
{
...
}

long ntp_set_time()
{
  while (ntp_time < 1000000)
  {
    ntpClient.update();
    ntp_time = ntpClient.getEpochTime();
    delay(1000);
  }

  Serial.print(ntpClient.getFormattedTime());
  Serial.print(" [TIME ] Time to set : " );
  Serial.println(ntp_time);

  return ntp_time;
}

Issue arises, due to ntp_time being global. So time is not updated.
A local variable ntp_time in function ntp_set_time would block, if connection to NTP servers fails.

My current solution:

long ntp_set_time()
{
  ntpClient.update();
  ntp_time = ntpClient.getEpochTime();
  
  while (ntp_time < 1000000)
  {
    ntpClient.update();
    ntp_time = ntpClient.getEpochTime();
    delay(1000);
  }

  Serial.print(ntpClient.getFormattedTime());
  Serial.print(" [TIME ] Time to set : " );
  Serial.println(ntp_time);

  return ntp_time;
}

This is just for information and not related to bug mentioned above.

[luckyhacky]

A proposal for retriggering as you suggested may be luckyhacky@9b198a9
you can test and give feedback.