31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * IPRT - RTTimerGetSystemGranularity, Ring-0 Driver, NT.
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * Copyright (C) 2006-2010 Oracle Corporation
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * This file is part of VirtualBox Open Source Edition (OSE), as
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * available from http://www.virtualbox.org. This file is free software;
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * you can redistribute it and/or modify it under the terms of the GNU
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * General Public License (GPL) as published by the Free Software
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * Foundation, in version 2 as it comes in the "COPYING" file of the
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * The contents of this file may alternatively be used under the terms
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * of the Common Development and Distribution License Version 1.0
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * VirtualBox OSE distribution, in which case the provisions of the
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * CDDL are applicable instead of those of the GPL.
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * You may elect to license modified versions of this file under the
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31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper/*******************************************************************************
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper* Header Files *
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper*******************************************************************************/
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de ReeperRTDECL(uint32_t) RTTimerGetSystemGranularity(void)
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * Get the default/max timer increment value, return it if ExSetTimerResolution
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * isn't available. According to the sysinternals guys NtQueryTimerResolution
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * is only available in userland and they find it equally annoying.
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper return ulTimeInc * 100; /* The value is in 100ns, the funny NT unit. */
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * Use the value returned by ExSetTimerResolution. Since the kernel is keeping
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper * count of these calls, we have to do two calls that cancel each other out.
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper ULONG ulResolution1 = g_pfnrtNtExSetTimerResolution(ulTimeInc, TRUE);
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper ULONG ulResolution2 = g_pfnrtNtExSetTimerResolution(0 /*ignored*/, FALSE);
31734da27b3f913bfb1da241a2e2571f33ab4629Mark de Reeper AssertMsg(ulResolution1 == ulResolution2, ("%ld, %ld\n", ulResolution1, ulResolution2)); /* not supposed to change it! */