Android screen-off timer set as 2 seconds

Customer reported that they set screen off timer as 2 seconds, however, the result is 6 seconds enter into suspend mode.

1. I tried to reproduce this issue by blow actions:

a. Power up Android, input Screen-off timer to 2 seconds in console.

$ sqlite3 /data/data/com.android.providers.settings/databases/settings.db
sqlite> update system set value="2000" where name="screen_off_timeout";
sqlite> .quit

b. Unlock the screen and wait for suspend message, about 6 seconds, I can see suspend message output from console. It shows what I see is exactly same as customer’s.

2. Locate the reason.

In “frameworks/base/services/java/com/android/server/PowerManagerService.java”, function private void setTimeoutLocked(long now, final long originalTimeoutOverride, int nextState), we can see below code. For nextState = SCREEN_BRIGHT, it will wait for mKeylightDelay and then enter next state.

switch (nextState)
{
    case SCREEN_BRIGHT:
        when = now + mKeylightDelay;
        break;
    case SCREEN_DIM:
        if (mDimDelay >= 0) {
            when = now + mDimDelay;
            break;
        } else {
            Slog.w(TAG, "mDimDelay=" + mDimDelay + " while trying to dim");
        }
    case SCREEN_OFF:
        synchronized (mLocks) {
            when = now + mScreenOffDelay;
        }
        break;
    default:
        when = now;
        break;
    }

I checked code, mKeylightDelay get its value “LONG_KEYLIGHT_DELAY” in function private void setScreenOffTimeoutsLocked(). And we can see macro definition in this file.

//                       time since last state:               time since last event:
    // The short keylight delay comes from secure settings; this is the default.
    private static final int SHORT_KEYLIGHT_DELAY_DEFAULT = 6000; // t+6 sec
    private static final int MEDIUM_KEYLIGHT_DELAY = 15000;       // t+15 sec
    private static final int LONG_KEYLIGHT_DELAY = 6000;        // t+6 sec
    private static final int LONG_DIM_TIME = 7000;              // t+N-5 sec

From above definition, we can see that is Android default design method, and we know why we will wait 6 seconds to enter suspend mode even we set screen-off timer as 2 seconds.

3. Solution.

a. We should keep minimum screen-off timer as 6 seconds, just following Android default design method.
b. I tried to modify the macro definition like below, and have a test, it can enter into suspend mode within 2 seconds. However, user experience is not good. Because 2 seconds is too short, e-reader panel response is slow, it is very easy to enter suspend mode, we have to wakeup it frequency.

//                       time since last state:               time since last event:
    // The short keylight delay comes from secure settings; this is the default.
    private static final int SHORT_KEYLIGHT_DELAY_DEFAULT = 1000; // t+6 sec
    private static final int MEDIUM_KEYLIGHT_DELAY = 9000;       // t+15 sec
    private static final int LONG_KEYLIGHT_DELAY = 1000;        // t+6 sec
    private static final int LONG_DIM_TIME = 2000;              // t+N-5 sec

Please tradeoff it.