C# Signature:

[DllImport("coredll.dll")]
static extern void SystemIdleTimerReset();

VB Signature:

Declare Sub SystemTimerReset Lib "coredll.dll" Alias "SystemIdleTimerReset" ()

User-Defined Types:

None.

Alternative Managed API:

None.

Notes:

To keep a device awake indefinitely, you can use SystemParametersInfo() (also in CoreDll) to query the three idle timeouts SPI_GETBATTERYIDLETIMEOUT, SPI_GETEXTERNALIDLETIMEOUT, and SPI_GETWAKEUPIDLETIMEOUT. Ignoring any values that are zero, use the minimum of these three values as your N, set a recurring timer to fire more often than every N seconds, and call SystemIdleTimerReset() every time it fires. When you're done with your critical operation, kill the timer, and the device will be able to sleep again. I tried this from C# and each idle-timeout value was 0, so I just called SystemIdleTimerReset() every 30 seconds during the critical operation.

You can also look at the configured timeouts at the registry key "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power".

Tips & Tricks:

Please add some!

Sample Code:

    /// <summary>
    /// This function resets a system timer that controls whether or not the
    /// device will automatically go into a suspended state.
    /// </summary>
    [DllImport("CoreDll.dll")]
    public static extern void SystemIdleTimerReset();

    private static int nDisableSleepCalls = 0;
    private static System.Threading.Timer preventSleepTimer = null;

    public static void DisableDeviceSleep()
    {
        nDisableSleepCalls++;
        if (nDisableSleepCalls == 1)
        {
            Debug.Assert(preventSleepTimer == null);
                // start a 30-second periodic timer
            preventSleepTimer = new System.Threading.Timer(new TimerCallback(PokeDeviceToKeepAwake),
                null, 0, 30 * 1000);
        }
    }

    public static void EnableDeviceSleep()
    {
        nDisableSleepCalls--;
        if (nDisableSleepCalls == 0)
        {
            Debug.Assert(preventSleepTimer != null);
            if (preventSleepTimer != null)
            {
                preventSleepTimer.Dispose();
                preventSleepTimer = null;
            }
        }
    }

    private static void PokeDeviceToKeepAwake(object extra)
    {
        try
        {
            SystemIdleTimerReset();
        }
        catch (Exception e)
        {
            // TODO
        }
    }

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