// Returns the ratio of a TPM clock second to one system time second
public static double MeasureClockRate(Tpm2 tpm)
{
const int MaxIter = 20;
int NumSamplesPerIter = 5;
int N = NumSamplesPerIter,
L = 0;
double[] tpmTimes = null;
double[] sysTimes = null;
double[] newTpmTimes = new double[N];
double[] newSysTimes = new double[N];
int iter = 0;
double stdDevSys = 0,
meanSys = 0,
stdDevTpm = 0,
meanTpm = 0;
int n = 0;
double sysTime = 0, tpmTime = 0;
do
{
tpmTimes = newTpmTimes;
sysTimes = newSysTimes;
TimeInfo tpmStart = null;
DateTime sysStart = DateTime.MinValue;
for (int i = L; i <= N; i++)
{
TimeInfo tpmStop = tpm.ReadClock();
DateTime sysStop = DateTime.Now;
if (tpmStart != null)
{
tpmTimes[i - 1] = tpmStop.time - tpmStart.time;
sysTimes[i - 1] = (sysStop - sysStart).TotalMilliseconds;
}
tpmStart = tpmStop;
sysStart = sysStop;
Thread.Sleep(600);
}
// Eliminate outliers that may be caused by the current thread having
// been preempted at a "wrong" point causing the measured rate distortion.
meanSys = meanTpm = stdDevSys = stdDevTpm = sysTime = tpmTime = 0;
for (int i = 0; i < N; i++)
{
meanSys += sysTimes[i];
meanTpm += tpmTimes[i];
}
meanSys /= N;
meanTpm /= N;
for (int i = 0; i < N; i++)
{
double d = (sysTimes[i] - meanSys);
stdDevSys += d * d;
d = (tpmTimes[i] - meanTpm);
stdDevTpm += d * d;
}
stdDevSys = Math.Sqrt(stdDevSys / N);
stdDevTpm = Math.Sqrt(stdDevTpm / N);
bool imprecise = stdDevSys / meanSys > 0.03 || stdDevTpm / meanTpm > 0.03;
if (imprecise)
{
newTpmTimes = new double[N + NumSamplesPerIter];
newSysTimes = new double[N + NumSamplesPerIter];
}
n = 0;
for (int i = 0; i < N; i++)
{
if (Math.Abs(sysTimes[i] - meanSys) < 2 * stdDevSys &&
Math.Abs(tpmTimes[i] - meanTpm) < 2 * stdDevTpm)
{
sysTime += sysTimes[i];
tpmTime += tpmTimes[i];
if (imprecise)
{
newSysTimes[n] = sysTimes[i];
newTpmTimes[n] = tpmTimes[i];
}
++n;
}
//else Console.Write("Dropped[{0}] = {1} ", i, sysTimes[i]);
}
if (!imprecise && n > 2)
{
break;
}
L = n;
N = L + NumSamplesPerIter;
} while (++iter < MaxIter);
if (iter == MaxIter)
{
Globs.Throw("The system is likely overloaded. Cannot do reliable time measurements.");
}
//Console.WriteLine("ITER {0}, MEAN {1:F0}->{2:F0}, SD {3:F1}; Good {4}; RATE {5:F2}",
// iter+1, meanSys, sysTime / n, stdDevSys, n, tpmTime / sysTime);
return(tpmTime / sysTime);
} // MeasureClockRate()
