sleep one extra second?

[ravelab]

I set it up like this:

setup() {
rtc.begin();
rtc.setAlarmSeconds(59);
rtc.enableAlarm(rtc.MATCH_SS);
Watchdog.enable()
}

loop() {
Watchdog.reset();
LED OFF
rtc.setSeconds(58);
rtc.standbyMode();
LED ON
}

I'm expecting it to sleep 1 second, but it actually sleeps 2 seconds. I'm also using Adafruit_SleepyDog for watchdog. Don't know if that matters.

Thanks

[moeskerv]

I can confirm this. Basically sleeping for some seconds only seems to always add 1s extra:

rtc.setSeconds(0);
rtc.setAlarmSeconds(0);
rtc.enableAlarm(rtc.MATCH_SS);
rtc.standbyMode();

-> Above results in a sleep for 1s.

rtc.setSeconds(0);
rtc.setAlarmSeconds(1);
rtc.enableAlarm(rtc.MATCH_SS);
rtc.standbyMode();

-> Above results in a sleep for 2 seconds.
And so on.
I'm using version RTCZero 1.6.0 on an Adafruit Feather M0. No SleepyDog in use.

[moeskerv]

Interestingly the ArduinoLowPower (which uses the RTC too) lib does the same on my Feather M0

LowPower.sleep(0); -> sleeps for 1s
LowPower.sleep(1000); -> sleeps for 2s

I tested with the TimedWakeup example: https://www.arduino.cc/en/Tutorial/LowPowerTimedWakeup

[moeskerv]

Might be a special behavior of the Adafruit M0 based Feathers?