reactos/subsystems/ntvdm/timer.c

/*
 * COPYRIGHT:       GPL - See COPYING in the top level directory
 * PROJECT:         ReactOS Virtual DOS Machine
 * FILE:            timer.c
 * PURPOSE:         Programmable Interval Timer emulation
 * PROGRAMMERS:     Aleksandar Andrejevic <theflash AT sdf DOT lonestar DOT org>
 */

/* INCLUDES *******************************************************************/

#define NDEBUG

#include "timer.h"
#include "pic.h"

/* PRIVATE VARIABLES **********************************************************/

static PIT_CHANNEL PitChannels[PIT_CHANNELS];

/* PUBLIC FUNCTIONS ***********************************************************/

VOID PitWriteCommand(BYTE Value)
{
    BYTE Channel = Value >> 6;
    BYTE Mode = (Value >> 1) & 0x07;

    /* Check if this is a counter latch command */
    if (((Value >> 4) & 3) == 0)
    {
        PitChannels[Channel].LatchSet = TRUE;
        PitChannels[Channel].LatchedValue = PitChannels[Channel].CurrentValue;
        return;
    }

    /* Set the access mode and reset flip-flops */
    PitChannels[Channel].AccessMode = (Value >> 4) & 3;
    PitChannels[Channel].Pulsed = FALSE;
    PitChannels[Channel].LatchSet = FALSE;
    PitChannels[Channel].InputFlipFlop = FALSE;
    PitChannels[Channel].OutputFlipFlop = FALSE;

    switch (Mode)
    {
        case 0:
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
        {
            PitChannels[Channel].Mode = Mode;
            break;
        }

        case 6:
        {
            PitChannels[Channel].Mode = PIT_MODE_RATE_GENERATOR;
            break;
        }

        case 7:
        {
            PitChannels[Channel].Mode = PIT_MODE_SQUARE_WAVE;
            break;
        }
    }
}

BYTE PitReadData(BYTE Channel)
{
    WORD CurrentValue = PitChannels[Channel].CurrentValue;
    BYTE AccessMode = PitChannels[Channel].AccessMode;

    /* Check if the value was latched */
    if (PitChannels[Channel].LatchSet)
    {
        CurrentValue = PitChannels[Channel].LatchedValue;

        if (AccessMode == 1 || AccessMode == 2)
        {
            /* The latched value was read as one byte */
            PitChannels[Channel].LatchSet = FALSE;
        }
    }

    /* Use the flip-flop for access mode 3 */
    if (AccessMode == 3)
    {
        AccessMode = PitChannels[Channel].InputFlipFlop ? 1 : 2;
        PitChannels[Channel].InputFlipFlop = !PitChannels[Channel].InputFlipFlop;

        /* Check if this was the last read for the latched value */
        if (!PitChannels[Channel].InputFlipFlop)
        {
            /* Yes, the latch value was read as two bytes */
            PitChannels[Channel].LatchSet = FALSE;
        }
    }

    switch (AccessMode)
    {
        case 1:
        {
            /* Low byte */
            return CurrentValue & 0x00FF;
        }

        case 2:
        {
            /* High byte */
            return CurrentValue >> 8;
        }
    }

    /* Shouldn't get here */
    return 0;
}

VOID PitWriteData(BYTE Channel, BYTE Value)
{
    BYTE AccessMode = PitChannels[Channel].AccessMode;

    /* Use the flip-flop for access mode 3 */
    if (PitChannels[Channel].AccessMode == 3)
    {
        AccessMode = PitChannels[Channel].InputFlipFlop ? 1 : 2;
        PitChannels[Channel].InputFlipFlop = !PitChannels[Channel].InputFlipFlop;
    }

    switch (AccessMode)
    {
        case 1:
        {
            /* Low byte */
            PitChannels[Channel].ReloadValue &= 0xFF00;
            PitChannels[Channel].ReloadValue |= Value;
            break;
        }

        case 2:
        {
            /* High byte */
            PitChannels[Channel].ReloadValue &= 0x00FF;
            PitChannels[Channel].ReloadValue |= Value << 8;
        }
    }
}

VOID PitDecrementCount()
{
    INT i;

    for (i = 0; i < PIT_CHANNELS; i++)
    {
        switch (PitChannels[i].Mode)
        {
            case PIT_MODE_INT_ON_TERMINAL_COUNT:
            {
                /* Decrement the value */
                PitChannels[i].CurrentValue--;

                /* Did it fall to the terminal count? */
                if (PitChannels[i].CurrentValue == 0 && !PitChannels[i].Pulsed)
                {
                    /* Yes, raise the output line */
                    if (i == 0) PicInterruptRequest(0);
                    PitChannels[i].Pulsed = TRUE;
                }
                break;
            }

            case PIT_MODE_RATE_GENERATOR:
            {
                /* Decrement the value */
                PitChannels[i].CurrentValue--;

                /* Did it fall to zero? */
                if (PitChannels[i].CurrentValue != 0) break;

                /* Yes, raise the output line and reload */
                if (i == 0) PicInterruptRequest(0);
                PitChannels[i].CurrentValue = PitChannels[i].ReloadValue;

                break;
            }

            case PIT_MODE_SQUARE_WAVE:
            {
                /* Decrement the value by 2 */
                PitChannels[i].CurrentValue -= 2;

                /* Did it fall to zero? */
                if (PitChannels[i].CurrentValue != 0) break;

                /* Yes, toggle the flip-flop */
                PitChannels[i].OutputFlipFlop = !PitChannels[i].OutputFlipFlop;

                /* Did this create a rising edge in the signal? */
                if (PitChannels[i].OutputFlipFlop)
                {
                    /* Yes, IRQ 0 if this is channel 0 */
                    if (i == 0) PicInterruptRequest(0);
                }

                /* Reload the value, but make sure it's even */
                if (PitChannels[i].ReloadValue % 2)
                {
                    /* It's odd, reduce it by 1 */
                    PitChannels[i].CurrentValue = PitChannels[i].ReloadValue - 1;
                }
                else
                {
                    /* It was even */
                    PitChannels[i].CurrentValue = PitChannels[i].ReloadValue;
                }

                break;
            }

            case PIT_MODE_SOFTWARE_STROBE:
            {
                // TODO: NOT IMPLEMENTED
                break;
            }

            case PIT_MODE_HARDWARE_ONE_SHOT:
            case PIT_MODE_HARDWARE_STROBE:
            {
                /* These modes do not work on x86 PCs */
                break;
            }
        }
    }
}

/* EOF */