You can call both SystemIdleTimerReset and SHIdleTimerReset to cover a wider range of devices(?)

static extern void SystemIdleTimerReset();

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

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.

    public static extern void SystemIdleTimerReset();

            SystemIdleTimerReset();