从时钟中断到线程调度的分析（二）

VOID FASTCALL HalpClockInterruptHandler(IN PKTRAP_FRAME TrapFrame)
{
    ULONG LastIncrement;
    KIRQL Irql;3

    /* Enter trap */
    KiEnterInterruptTrap(TrapFrame);

    /* Start the interrupt */
    if (ghhghhjvc(CLOCK2_LEVEL, PRIMARY_VECTOR_BASE, &Irql))
    {
        /* Update the performance counter */
        HalpPerfCounter.QuadPart += HalpCurrentRollOver;
        HalpPerfCounterCutoff = KiEnableTimerWatchdog;

        /* Save increment */
        LastIncrement = HalpCurrentTimeIncrement;

        /* Check if someone changed the time rate */
        if (HalpClockSetMSRate)
        {
            /* Update the global values */
            HalpCurrentTimeIncrement = HalpRolloverTable[HalpNextMSRate - 1].Increment;
            HalpCurrentRollOver = HalpRolloverTable[HalpNextMSRate - 1].RollOver;

            /* Set new timer rollover */
            HalpSetTimerRollOver((USHORT)HalpCurrentRollOver);

            /* We‘re done */
            HalpClockSetMSRate = FALSE;
        }

        /* Update the system time -- the kernel will exit this trap  */
        KeUpdateSystemTime(TrapFrame, LastIncrement, Irql);  更新系统时间
    } 

    /* Spurious, just end the interrupt */
    KiEoiHelper(TrapFrame);
}