/* $Id$ */
/** @file
* IPRT - RTTimerGetSystemGranularity, Ring-0 Driver, NT.
*/
/*
* Copyright (C) 2006-2010 Oracle Corporation
*
* This file is part of VirtualBox Open Source Edition (OSE), as
* available from http://www.virtualbox.org. This file is free software;
* you can redistribute it and/or modify it under the terms of the GNU
* General Public License (GPL) as published by the Free Software
* Foundation, in version 2 as it comes in the "COPYING" file of the
* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL) only, as it comes in the "COPYING.CDDL" file of the
* VirtualBox OSE distribution, in which case the provisions of the
* CDDL are applicable instead of those of the GPL.
*
* You may elect to license modified versions of this file under the
* terms and conditions of either the GPL or the CDDL or both.
*/
/*******************************************************************************
* Header Files *
*******************************************************************************/
#include "the-nt-kernel.h"
#include <iprt/timer.h>
#include <iprt/err.h>
#include <iprt/asm.h>
#include <iprt/assert.h>
#include "internal-r0drv-nt.h"
#include "internal/magics.h"
RTDECL(uint32_t) RTTimerGetSystemGranularity(void)
{
/*
* Get the default/max timer increment value, return it if ExSetTimerResolution
* isn't available. According to the sysinternals guys NtQueryTimerResolution
* is only available in userland and they find it equally annoying.
*/
ULONG ulTimeInc = KeQueryTimeIncrement();
if (!g_pfnrtNtExSetTimerResolution)
return ulTimeInc * 100; /* The value is in 100ns, the funny NT unit. */
/*
* Use the value returned by ExSetTimerResolution. Since the kernel is keeping
* count of these calls, we have to do two calls that cancel each other out.
*/
ULONG ulResolution1 = g_pfnrtNtExSetTimerResolution(ulTimeInc, TRUE);
ULONG ulResolution2 = g_pfnrtNtExSetTimerResolution(0 /*ignored*/, FALSE);
AssertMsg(ulResolution1 == ulResolution2, ("%ld, %ld\n", ulResolution1, ulResolution2)); /* not supposed to change it! */
return ulResolution2 * 100; /* NT -> ns */
}