RTC_WAKEUP doesn't work on all devices

Question

I am scheduling an alarm as below (excuse the ugly code; I was testing):

int code = new Random().nextInt();
    Intent bIntent = new Intent(LaunchActivityReceiver.LAUNCH_ACTIVITY_ACTION);
    bIntent.setClass(mContext, LaunchActivityReceiver.class);
    PendingIntent broadcastIntent = PendingIntent.getBroadcast(mContext, code, bIntent, PendingIntent.FLAG_CANCEL_CURRENT);
    alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), broadcastIntent);

Permissions:

    <uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.GET_ACCOUNTS"/>
<uses-permission android:name="android.permission.USE_CREDENTIALS" />
<uses-permission android:name="android.permission.MANAGE_ACCOUNTS"/>
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
<uses-permission android:name="android.permission.WAKE_LOCK"/>
<uses-permission android:name="android.permission.DISABLE_KEYGUARD"/>

The calendar is set to one minute in the future (I am sure of this). As an aside, I'm aware one minute is very short for an Alarm but it's for testing. I noticed this issue on an 8 hour Alarm. If the screen is on, the BroadcastReceiver fires exactly one minute later (it does nothing except print to LogCat). It doesn't matter if the app is in the foreground or not. OK, great.

If the screen is off, though, I get dramatically odd behavior. I've seen it fire in 1.5 minutes, 3 minutes, 5 minutes, and never (got tired of waiting). As soon as I turn on the screen, though, the alarm fires if it hadn't already. It's like RTC_WAKEUP is being treated as just RTC.

This only happens on some cheap-o Chinese tablet. It is running 5.1, though. I don't understand this odd behavior.

This seems to be a common problem, but the solutions for others didn't work. I am not changing timezones or the time at all, I don't need to wakelock the BroadcastReceiver since it does nothing but print to the log, and it's not a bug with the Calendar (if it was, it wouldn't work every time the device isn't sleeping). Any ideas?

Answer 1

It never worked with that device, no matter which options I tried. I think that device's ROM is just broken in that regard.