175 lines
3.6 KiB
C
175 lines
3.6 KiB
C
/*++
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Copyright (c) 1994 Microsoft Corporation
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Module Name:
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xxclock.c
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Abstract:
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This module implements the function necesssary to change the clock
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interrupt rate.
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Author:
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David N. Cutler (davec) 7-Feb-1994
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Environment:
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Kernel mode only.
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Revision History:
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--*/
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#include "halp.h"
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#include "eisa.h"
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//
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// Define clock count and time table.
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//
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typedef struct _COUNT_ENTRY {
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ULONG Count;
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ULONG Time;
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} COUNT_ENTRY, *PCOUNT_ENTRY;
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COUNT_ENTRY TimeTable[] = {
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{1197, 10032},
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{2394, 20064},
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{3591, 30096},
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{4767, 39952},
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{5964, 49984},
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{7161, 60016},
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{8358, 70048},
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{9555, 80080},
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{10731, 89936},
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{11928, 99968}
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};
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//
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// Define global data used to communicate new clock rates to the clock
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// interrupt service routine.
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//
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ULONG HalpCurrentTimeIncrement;
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ULONG HalpNextIntervalCount;
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ULONG HalpNextTimeIncrement;
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ULONG HalpNewTimeIncrement;
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VOID
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HalpProgramIntervalTimer(
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IN ULONG IntervalCount
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)
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/*++
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Routine Description:
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This function is called to program the interval timer. It is used during
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Phase 1 initialization to start the heartbeat timer. It also used by
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the clock interrupt interrupt routine to change the hearbeat timer rate
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when a call to HalSetTimeIncrement has been made in the previous time slice.
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Arguments:
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IntervalCount - Supplies cound value to be placed in the timer/counter.
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Return Value:
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None
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--*/
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{
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PEISA_CONTROL controlBase;
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TIMER_CONTROL timerControl;
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//
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// Set the system clock timer to the correct mode.
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//
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timerControl.BcdMode = 0;
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timerControl.Mode = TM_SQUARE_WAVE;
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timerControl.SelectByte = SB_LSB_THEN_MSB;
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timerControl.SelectCounter = SELECT_COUNTER_0;
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controlBase = HalpEisaControlBase;
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WRITE_REGISTER_UCHAR(&controlBase->CommandMode1, *((PUCHAR) &timerControl));
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//
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// Set the system clock timer to the correct frequency.
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//
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WRITE_REGISTER_UCHAR(&controlBase->Timer1, (UCHAR)IntervalCount);
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WRITE_REGISTER_UCHAR(&controlBase->Timer1, (UCHAR)(IntervalCount >> 8));
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}
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ULONG
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HalSetTimeIncrement (
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IN ULONG DesiredIncrement
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)
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/*++
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Routine Description:
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This function is called to set the clock interrupt rate to the frequency
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required by the specified time increment value.
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N.B. This function is only executed on the processor that keeps the
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system time.
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Arguments:
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DesiredIncrement - Supplies desired number of 100ns units between clock
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interrupts.
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Return Value:
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The actual time increment in 100ns units.
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--*/
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{
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ULONG Index;
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KIRQL OldIrql;
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//
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// Raise IRQL to the highest level, set the new clock interrupt
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// parameters, lower IRQl, and return the new time increment value.
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//
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KeRaiseIrql(HIGH_LEVEL, &OldIrql);
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//
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// The new clock count value is selected from a precomputed table of
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// count/time pairs. The values in the table were selected for their
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// accuracy and closeness to the values of 1ms, 2ms, 3ms, etc. to 10ms.
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//
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// N.B. The NT executive guarantees that this function will never
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// be called with the desired incrment less than the minimum
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// increment or greater than the maximum increment.
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//
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for (Index = 0; Index < sizeof(TimeTable) / sizeof(COUNT_ENTRY); Index += 1) {
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if (DesiredIncrement <= TimeTable[Index].Time) {
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break;
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}
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}
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if (DesiredIncrement < TimeTable[Index].Time) {
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Index -= 1;
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}
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HalpNextIntervalCount = TimeTable[Index].Count;
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HalpNewTimeIncrement = TimeTable[Index].Time;
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KeLowerIrql(OldIrql);
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return HalpNewTimeIncrement;
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}
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