Question

Basically I am writing a simple bit of code to increment every one second and display the time and date, which is frustrating me, and I’m sure I’m overlooking something obvious.

So I will display the time as MJD (Modified Julian Date) HH:MM:SS but also allow for a hardcoded MJD to represent a leap second event, and then correctly display the leap second.

It kind of works, however it skips out 23:59:59.

I eventually plan on porting to plain old AVR so I don’t really want to mess around with arduino libraries.

int second = 0, minute = 0, hour = 0;
long mjd = 55000;
long leap = 55964;

void setup()
{
    Serial.begin(9600);
    Serial.print("MDJ ");
    Serial.print(mjd);
    Serial.print(" ");
    Serial.print(hour);
    Serial.print(":");
    Serial.print(minute);
    Serial.print(":");
    Serial.println(second);

}

void loop()
{
    second++;
    if (mjd == leap && hour == 23 && minute == 59 && second == 59) {
        second++;
    } else {
        if (second > 59) {
            minute++;
            second = 0; // reset seconds to zero
        }
    }
    if (minute > 59) {
        hour++;
        minute = 0;
    }

    if (hour > 23) {
        mjd++;
        hour = 0;
    }

    Serial.print("MDJ ");
    Serial.print(mjd);
    Serial.print(" ");
    if (hour < 10)
        Serial.print("0");
    Serial.print(hour);
    Serial.print(":");
    if (minute < 10)
        Serial.print("0");
    Serial.print(minute);
    Serial.print(":");
    if (second < 10)
        Serial.print("0");
    Serial.println(second);
    delay(1000);
}

Answer 1

I think you might need only a very small change:

if (mjd == leap && hour == 23 && minute == 59 && second == 60) {
    // allow 23:59:60
} else {
    ...

The problem appears to be that you increment to the next second, and then if it’s 23:59:59 and a leap second is indicated, you increment again to 60 (skipping 59).

What you probably want to do is roll over the second unless it is a leap second.