86 lines
2.8 KiB
C#
86 lines
2.8 KiB
C#
///////////////////////////////////////////////////////////////////////////////
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//
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// Microsoft Research Singularity
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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// Note:
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//
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// HalClock is expected to call PMClock's time maintenance
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// functions with a spin lock held.
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namespace Microsoft.Singularity.Hal
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{
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using Microsoft.Singularity.Hal.Acpi;
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using System;
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using System.Diagnostics;
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using System.Runtime.CompilerServices;
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using System.Runtime.InteropServices;
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using System.Threading;
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[ CLSCompliant(false) ]
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internal class PMClock
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{
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PMTimer pmTimer;
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ulong kernelTicksTotal;
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ulong pmResidual;
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uint pmLastUpdate;
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internal PMClock(PMTimer timer)
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{
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this.pmTimer = timer;
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this.kernelTicksTotal = 0;
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this.pmResidual = 0;
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this.pmLastUpdate = pmTimer.Value;
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}
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[NoHeapAllocation]
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private static ulong PMTicksToKernelTicks(ulong pmTicks)
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{
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// REVIEW: Does this need to be a ulong?
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//
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// PM frequency is 3579545Hz. Kernel tick frequency is 10MHz.
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// The conversion is:
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// kTicks = pmTicks * 10000000 / 3579545
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// = pmTicks * (2 + 0xcb2cb8bed / 0x1000000000)
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// = pmTicks * (0x2cb / 0x100 + 0x2cb / 0x100000 +
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// 0x8bed / 0x1000000000)
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ulong tmp = pmTicks * 0x2cb;
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return (tmp >> 8) + (tmp >> 20) + ((pmTicks * 0x8bed) >> 36);
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}
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[NoHeapAllocation]
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private static uint PmDeltaTicks(uint pmNow, uint pmLast)
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{
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// We unconditionally round down to 24-bits as
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// values from PM timer may be 24-bit or 32-bit.
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return (pmNow - pmLast) & 0xffffff;
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}
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[NoHeapAllocation]
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internal ulong GetKernelTicks()
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{
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uint pmNow = pmTimer.Value;
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uint pmDelta = PmDeltaTicks(pmNow, this.pmLastUpdate);
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return this.kernelTicksTotal +
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PMTicksToKernelTicks(this.pmResidual + pmDelta);
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}
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[NoHeapAllocation]
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internal void Update()
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{
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uint pmNow = pmTimer.Value;
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this.pmResidual += PmDeltaTicks(pmNow, this.pmLastUpdate);
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// Transfer time from residual to accumulated
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// time in one second intervals since there is
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// an integral relationship between the two.
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while (this.pmResidual >= PMTimer.FrequencyHz) {
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this.kernelTicksTotal += 10000000; // Kernel tick freq
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this.pmResidual -= PMTimer.FrequencyHz;
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}
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this.pmLastUpdate = pmNow;
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}
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}
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}
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