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/* $Id: RTTimerGetSystemGranularity-r0drv-nt.cpp $ */
/** @file
* IPRT - RTTimerGetSystemGranularity, Ring-0 Driver, NT.
*/
/*
* Copyright (C) 2006-2023 Oracle and/or its affiliates.
*
* This file is part of VirtualBox base platform packages, as
* available from https://www.virtualbox.org.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, in version 3 of the
* License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses>.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
* in the VirtualBox 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.
*
* SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
*/
/*********************************************************************************************************************************
* Header Files *
*********************************************************************************************************************************/
#include "the-nt-kernel.h"
#include <iprt/timer.h>
#include <iprt/errcore.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.
*/
g_pfnrtNtExSetTimerResolution(ulTimeInc, TRUE);
ULONG ulResolution = g_pfnrtNtExSetTimerResolution(0 /*ignored*/, FALSE);
return ulResolution * 100; /* NT -> ns */
}
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