#include "ntvdm.h"
#include <debug.h>
#include "emulator.h"
#include "cpu/cpu.h"
#include "int32.h"
#include "dos.h"
#include "dos/dem.h"
#include "country.h"
#include "device.h"
#include "handle.h"
#include "dosfiles.h"
#include "memory.h"
#include "process.h"
#include "himem.h"
#include "bios/bios.h"
#include "io.h"
#include "hardware/ps2.h"
#include "emsdrv.h"

Include dependency graph for dos.c:

Macros
#define	NDEBUG

Functions
static BOOLEAN	DosChangeDrive (BYTE Drive)

static BOOLEAN	DosChangeDirectory (LPSTR Directory)

static BOOLEAN	DosIsFileOnCdRom (VOID)

BOOLEAN	DosControlBreak (VOID)

VOID WINAPI	DosInt20h (LPWORD Stack)

VOID WINAPI	DosInt21h (LPWORD Stack)

VOID WINAPI	DosBreakInterrupt (LPWORD Stack)

VOID WINAPI	DosAbsoluteRead (LPWORD Stack)

VOID WINAPI	DosAbsoluteWrite (LPWORD Stack)

VOID WINAPI	DosInt27h (LPWORD Stack)

VOID WINAPI	DosIdle (LPWORD Stack)

VOID WINAPI	DosFastConOut (LPWORD Stack)

VOID WINAPI	DosInt2Ah (LPWORD Stack)

VOID WINAPI	DosInt2Fh (LPWORD Stack)

BOOLEAN	DosKRNLInitialize (VOID)

Variables
CALLBACK16	DosContext

PDOS_DATA	DosData

PDOS_SYSVARS	SysVars

PDOS_SDA	Sda

Macro Definition Documentation

◆ NDEBUG

#define NDEBUG

Definition at line 14 of file dos.c.

Function Documentation

◆ DosAbsoluteRead()

VOID WINAPI DosAbsoluteRead ( LPWORD Stack )

Definition at line 2032 of file dos.c.

{
    /*
     * This call should leave the flags on the stack for some reason,
     * so move the stack by one word.
     * See: http://www.techhelpmanual.com/565-int_25h_26h__absolute_disk_read_write.html
     */
    Stack[STACK_INT_NUM] = Stack[STACK_IP];
    Stack[STACK_IP] = Stack[STACK_CS];
    Stack[STACK_CS] = Stack[STACK_FLAGS];
    setSP(LOWORD(getSP() - 2));
 
    // TODO: NOT IMPLEMENTED;
    UNIMPLEMENTED;
 
    /* General failure */
    setAX(0x800C);
    Stack[STACK_FLAGS - 1] |= EMULATOR_FLAG_CF;
}

Referenced by DosKRNLInitialize().

◆ DosAbsoluteWrite()

VOID WINAPI DosAbsoluteWrite ( LPWORD Stack )

Definition at line 2052 of file dos.c.

{
    /*
     * This call should leave the flags on the stack for some reason,
     * so move the stack by one word.
     * See: http://www.techhelpmanual.com/565-int_25h_26h__absolute_disk_read_write.html
     */
    Stack[STACK_INT_NUM] = Stack[STACK_IP];
    Stack[STACK_IP] = Stack[STACK_CS];
    Stack[STACK_CS] = Stack[STACK_FLAGS];
    setSP(LOWORD(getSP() - 2));
 
    // TODO: NOT IMPLEMENTED;
    UNIMPLEMENTED;
 
    /* General failure */
    setAX(0x800C);
    Stack[STACK_FLAGS - 1] |= EMULATOR_FLAG_CF;
}

Referenced by DosKRNLInitialize().

◆ DosBreakInterrupt()

VOID WINAPI DosBreakInterrupt ( LPWORD Stack )

Definition at line 2026 of file dos.c.

{
    /* Set CF to terminate the running process */
    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
}

Referenced by DosKRNLInitialize().

◆ DosChangeDirectory()

static BOOLEAN DosChangeDirectory ( LPSTR Directory )

static

Definition at line 78 of file dos.c.

{
    BYTE DriveNumber;
    DWORD Attributes;
    LPSTR Path;
    CHAR CurrentDirectory[MAX_PATH];
    CHAR DosDirectory[DOS_DIR_LENGTH];
 
    /* Make sure the directory path is not too long */
    if (strlen(Directory) >= DOS_DIR_LENGTH)
    {
        Sda->LastErrorCode = ERROR_PATH_NOT_FOUND;
        return FALSE;
    }
 
    /* Check whether the directory string is of format "X:..." */
    if (strlen(Directory) >= 2 && Directory[1] == ':')
    {
        /* Get the drive number */
        DriveNumber = RtlUpperChar(Directory[0]) - 'A';
 
        /* Make sure the drive exists */
        if (DriveNumber >= SysVars->NumLocalDrives)
        {
            Sda->LastErrorCode = ERROR_PATH_NOT_FOUND;
            return FALSE;
        }
    }
    else
    {
        /* Keep the current drive number */
        DriveNumber = Sda->CurrentDrive;
    }
 
    /* Get the file attributes */
    Attributes = GetFileAttributesA(Directory);
 
    /* Make sure the path exists and is a directory */
    if ((Attributes == INVALID_FILE_ATTRIBUTES) ||
       !(Attributes & FILE_ATTRIBUTE_DIRECTORY))
    {
        Sda->LastErrorCode = ERROR_PATH_NOT_FOUND;
        return FALSE;
    }
 
    /* Check if this is the current drive */
    if (DriveNumber == Sda->CurrentDrive)
    {
        /* Change the directory */
        if (!SetCurrentDirectoryA(Directory))
        {
            Sda->LastErrorCode = LOWORD(GetLastError());
            return FALSE;
        }
    }
 
    /* Get the (possibly new) current directory (needed if we specified a relative directory) */
    if (!GetCurrentDirectoryA(sizeof(CurrentDirectory), CurrentDirectory))
    {
        // TODO: Use some kind of default path?
        return FALSE;
    }
 
    /* Convert it to a DOS path */
    if (!GetShortPathNameA(CurrentDirectory, DosDirectory, sizeof(DosDirectory)))
    {
        // TODO: Use some kind of default path?
        return FALSE;
    }
 
    /* Get the directory part of the path and set the current directory for the drive */
    Path = strchr(DosDirectory, '\\');
    if (Path != NULL)
    {
        Path++; // Skip the backslash
        strncpy(DosData->CurrentDirectories[DriveNumber], Path, DOS_DIR_LENGTH);
    }
    else
    {
        DosData->CurrentDirectories[DriveNumber][0] = '\0';
    }
 
    /* Return success */
    return TRUE;
}

Referenced by DosInt21h().

◆ DosChangeDrive()

static BOOLEAN DosChangeDrive ( BYTE Drive )

static

Definition at line 52 of file dos.c.

{
    CHAR DirectoryPath[DOS_CMDLINE_LENGTH + 1];
 
    /* Make sure the drive exists */
    if (Drive >= SysVars->NumLocalDrives) return FALSE;
 
    RtlZeroMemory(DirectoryPath, sizeof(DirectoryPath));
 
    /* Find the path to the new current directory */
    snprintf(DirectoryPath,
             DOS_CMDLINE_LENGTH,
             "%c:\\%s",
             'A' + Drive,
             DosData->CurrentDirectories[Drive]);
 
    /* Change the current directory of the process */
    if (!SetCurrentDirectoryA(DirectoryPath)) return FALSE;
 
    /* Set the current drive */
    Sda->CurrentDrive = Drive;
 
    /* Return success */
    return TRUE;
}

Referenced by DosInt21h().

◆ DosControlBreak()

BOOLEAN DosControlBreak ( VOID )

Definition at line 181 of file dos.c.

{
    setCF(0);
 
    /* Print an extra newline */
    DosPrintCharacter(DOS_OUTPUT_HANDLE, '\r');
    DosPrintCharacter(DOS_OUTPUT_HANDLE, '\n');
 
    /* Call interrupt 0x23 */
    Int32Call(&DosContext, 0x23);
 
    if (getCF())
    {
        DosTerminateProcess(Sda->CurrentPsp, 0, 0);
        return TRUE;
    }
 
    return FALSE;
}

Referenced by DosInt21h(), and DosReadLineBuffered().

◆ DosFastConOut()

VOID WINAPI DosFastConOut ( LPWORD Stack )

Definition at line 2090 of file dos.c.

{
    /*
     * This is the DOS 2+ Fast Console Output Interrupt.
     * The default handler under DOS 2.x and 3.x simply calls INT 10h/AH=0Eh.
     *
     * See Ralf Brown: http://www.ctyme.com/intr/rb-4124.htm
     * for more information.
     */
 
    /* Save AX and BX */
    USHORT AX = getAX();
    USHORT BX = getBX();
 
    /*
     * Set the parameters:
     * AL contains the character to print (already set),
     * BL contains the character attribute,
     * BH contains the video page to use.
     */
    setBL(DOS_CHAR_ATTRIBUTE);
    setBH(Bda->VideoPage);
 
    /* Call the BIOS INT 10h, AH=0Eh "Teletype Output" */
    setAH(0x0E);
    Int32Call(&DosContext, BIOS_VIDEO_INTERRUPT);
 
    /* Restore AX and BX */
    setBX(BX);
    setAX(AX);
}

Referenced by DosKRNLInitialize().

◆ DosIdle()

VOID WINAPI DosIdle ( LPWORD Stack )

Definition at line 2081 of file dos.c.

{
    /*
     * This will set the carry flag on the first call (to repeat the BOP),
     * and clear it in the next, so that exactly one HLT occurs.
     */
    setCF(!getCF());
}

Referenced by DosKRNLInitialize().

◆ DosInt20h()

VOID WINAPI DosInt20h ( LPWORD Stack )

Definition at line 201 of file dos.c.

{
    /*
     * This is the exit interrupt (alias to INT 21h, AH=00h).
     * CS must be the PSP segment.
     */
    DosTerminateProcess(Stack[STACK_CS], 0, 0);
}

Referenced by DosKRNLInitialize().

◆ DosInt21h()

VOID WINAPI DosInt21h ( LPWORD Stack )

Definition at line 210 of file dos.c.

{
    BYTE Character;
    SYSTEMTIME SystemTime;
    PCHAR String;
 
    Sda->InDos++;
 
    /* Save the value of SS:SP on entry in the PSP */
    SEGMENT_TO_PSP(Sda->CurrentPsp)->LastStack =
    MAKELONG(getSP() + (STACK_FLAGS + 1) * 2, getSS());
 
    /* Check the value in the AH register */
    switch (getAH())
    {
        /* Terminate Program */
        case 0x00:
        {
            /* CS must be the PSP segment */
            DosTerminateProcess(Stack[STACK_CS], 0, 0);
            break;
        }
 
        /* Read Character from STDIN with Echo */
        case 0x01:
        {
            DPRINT("INT 21h, AH = 01h\n");
 
            Character = DosReadCharacter(DOS_INPUT_HANDLE, TRUE);
            if (Character == 0x03 && DosControlBreak()) break;
 
            setAL(Character);
            break;
        }
 
        /* Write Character to STDOUT */
        case 0x02:
        {
            // FIXME: Under DOS 2+, output handle may be redirected!!!!
            Character = getDL();
            DosPrintCharacter(DOS_OUTPUT_HANDLE, Character);
 
            /*
             * We return the output character (DOS 2.1+).
             * Also, if we're going to output a TAB, then
             * don't return a TAB but a SPACE instead.
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2554.htm
             * for more information.
             */
            setAL(Character == '\t' ? ' ' : Character);
            break;
        }
 
        /* Read Character from STDAUX */
        case 0x03:
        {
            // FIXME: Really read it from STDAUX!
            DPRINT1("INT 16h, 03h: Read character from STDAUX is HALFPLEMENTED\n");
            // setAL(DosReadCharacter());
            break;
        }
 
        /* Write Character to STDAUX */
        case 0x04:
        {
            // FIXME: Really write it to STDAUX!
            DPRINT1("INT 16h, 04h: Write character to STDAUX is HALFPLEMENTED\n");
            // DosPrintCharacter(getDL());
            break;
        }
 
        /* Write Character to Printer */
        case 0x05:
        {
            // FIXME: Really write it to printer!
            DPRINT1("INT 16h, 05h: Write character to printer is HALFPLEMENTED -\n\n");
            DPRINT1("0x%p\n", getDL());
            DPRINT1("\n\n-----------\n\n");
            break;
        }
 
        /* Direct Console I/O */
        case 0x06:
        {
            Character = getDL();
 
            // FIXME: Under DOS 2+, output handle may be redirected!!!!
 
            if (Character != 0xFF)
            {
                /* Output */
                DosPrintCharacter(DOS_OUTPUT_HANDLE, Character);
 
                /*
                 * We return the output character (DOS 2.1+).
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2558.htm
                 * for more information.
                 */
                setAL(Character);
            }
            else
            {
                /* Input */
                if (DosCheckInput())
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_ZF;
                    setAL(DosReadCharacter(DOS_INPUT_HANDLE, FALSE));
                }
                else
                {
                    /* No character available */
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_ZF;
                    setAL(0x00);
                }
            }
 
            break;
        }
 
        /* Direct Character Input without Echo */
        case 0x07:
        {
            DPRINT("Direct char input without echo\n");
            setAL(DosReadCharacter(DOS_INPUT_HANDLE, FALSE));
            break;
        }
 
        /* Character Input without Echo */
        case 0x08:
        {
            DPRINT("Char input without echo\n");
 
            Character = DosReadCharacter(DOS_INPUT_HANDLE, FALSE);
            if (Character == 0x03 && DosControlBreak()) break;
 
            setAL(Character);
            break;
        }
 
        /* Write String to STDOUT */
        case 0x09:
        {
            String = (PCHAR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            while (*String != '$')
            {
                DosPrintCharacter(DOS_OUTPUT_HANDLE, *String);
                String++;
            }
 
            /*
             * We return the terminating character (DOS 2.1+).
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2562.htm
             * for more information.
             */
            setAL('$'); // *String
            break;
        }
 
        /* Read Buffered Input */
        case 0x0A:
        {
            PDOS_INPUT_BUFFER InputBuffer = (PDOS_INPUT_BUFFER)SEG_OFF_TO_PTR(getDS(), getDX());
 
            DPRINT("Read Buffered Input\n");
            if (InputBuffer->MaxLength == 0) break;
 
            /* Read from standard input */
            InputBuffer->Length = DosReadLineBuffered(
                DOS_INPUT_HANDLE,
                MAKELONG(getDX() + FIELD_OFFSET(DOS_INPUT_BUFFER, Buffer), getDS()),
                InputBuffer->MaxLength
            );
 
            break;
        }
 
        /* Get STDIN Status */
        case 0x0B:
        {
            setAL(DosCheckInput() ? 0xFF : 0x00);
            break;
        }
 
        /* Flush Buffer and Read STDIN */
        case 0x0C:
        {
            BYTE InputFunction = getAL();
 
            /* Flush STDIN buffer */
            DosFlushFileBuffers(DOS_INPUT_HANDLE);
 
            /*
             * If the input function number contained in AL is valid, i.e.
             * AL == 0x01 or 0x06 or 0x07 or 0x08 or 0x0A, call ourselves
             * recursively with AL == AH.
             */
            if (InputFunction == 0x01 || InputFunction == 0x06 ||
                InputFunction == 0x07 || InputFunction == 0x08 ||
                InputFunction == 0x0A)
            {
                /* Call ourselves recursively */
                setAH(InputFunction);
                DosInt21h(Stack);
            }
            break;
        }
 
        /* Disk Reset */
        case 0x0D:
        {
            PDOS_PSP PspBlock = SEGMENT_TO_PSP(Sda->CurrentPsp);
 
            // TODO: Flush what's needed.
            DPRINT1("INT 21h, 0Dh is UNIMPLEMENTED\n");
 
            /* Clear CF in DOS 6 only */
            if (PspBlock->DosVersion == 0x0006)
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
 
            break;
        }
 
        /* Set Default Drive  */
        case 0x0E:
        {
            DosChangeDrive(getDL());
            setAL(SysVars->NumLocalDrives);
            break;
        }
 
        /* NULL Function for CP/M Compatibility */
        case 0x18:
        {
            /*
             * This function corresponds to the CP/M BDOS function
             * "get bit map of logged drives", which is meaningless
             * under MS-DOS.
             *
             * For: PTS-DOS 6.51 & S/DOS 1.0 - EXTENDED RENAME FILE USING FCB
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2584.htm
             * for more information.
             */
            setAL(0x00);
            break;
        }
 
        /* Get Default Drive */
        case 0x19:
        {
            setAL(Sda->CurrentDrive);
            break;
        }
 
        /* Set Disk Transfer Area */
        case 0x1A:
        {
            Sda->DiskTransferArea = MAKELONG(getDX(), getDS());
            break;
        }
 
        /* NULL Function for CP/M Compatibility */
        case 0x1D:
        case 0x1E:
        {
            /*
             * Function 0x1D corresponds to the CP/M BDOS function
             * "get bit map of read-only drives", which is meaningless
             * under MS-DOS.
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2592.htm
             * for more information.
             *
             * Function 0x1E corresponds to the CP/M BDOS function
             * "set file attributes", which was meaningless under MS-DOS 1.x.
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2593.htm
             * for more information.
             */
            setAL(0x00);
            break;
        }
 
        /* NULL Function for CP/M Compatibility */
        case 0x20:
        {
            /*
             * This function corresponds to the CP/M BDOS function
             * "get/set default user (sublibrary) number", which is meaningless
             * under MS-DOS.
             *
             * For: S/DOS 1.0+ & PTS-DOS 6.51+ - GET OEM REVISION
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2596.htm
             * for more information.
             */
            setAL(0x00);
            break;
        }
 
        /* Set Interrupt Vector */
        case 0x25:
        {
            ULONG FarPointer = MAKELONG(getDX(), getDS());
            DPRINT1("Setting interrupt 0x%02X to %04X:%04X ...\n",
                    getAL(), HIWORD(FarPointer), LOWORD(FarPointer));
 
            /* Write the new far pointer to the IDT */
            ((PULONG)BaseAddress)[getAL()] = FarPointer;
            break;
        }
 
        /* Create New PSP */
        case 0x26:
        {
            /* DOS 2+ assumes that the caller's CS is the segment of the PSP to copy */
            DosClonePsp(getDX(), Stack[STACK_CS]);
            break;
        }
 
        /* Parse Filename into FCB */
        case 0x29:
        {
            PCHAR FileName = (PCHAR)SEG_OFF_TO_PTR(getDS(), getSI());
            PDOS_FCB Fcb = (PDOS_FCB)SEG_OFF_TO_PTR(getES(), getDI());
            BYTE Options = getAL();
            CHAR FillChar = ' ';
            UINT i;
 
            if (FileName[1] == ':')
            {
                /* Set the drive number */
                Fcb->DriveNumber = RtlUpperChar(FileName[0]) - 'A' + 1;
 
                /* Skip to the file name part */
                FileName += 2;
            }
            else
            {
                /* No drive number specified */
                if (Options & (1 << 1)) Fcb->DriveNumber = Sda->CurrentDrive + 1;
                else Fcb->DriveNumber = 0;
            }
 
            /* Parse the file name */
            i = 0;
            while ((*FileName > 0x20) && (i < 8))
            {
                if (*FileName == '.') break;
                else if (*FileName == '*')
                {
                    FillChar = '?';
                    break;
                }
 
                Fcb->FileName[i++] = RtlUpperChar(*FileName++);
            }
 
            /* Fill the whole field with blanks only if bit 2 is not set */
            if ((FillChar != ' ') || (i != 0) || !(Options & (1 << 2)))
            {
                for (; i < 8; i++) Fcb->FileName[i] = FillChar;
            }
 
            /* Skip to the extension part */
            while (*FileName > 0x20 && *FileName != '.') FileName++;
            if (*FileName == '.') FileName++;
 
            /* Now parse the extension */
            i = 0;
            FillChar = ' ';
 
            while ((*FileName > 0x20) && (i < 3))
            {
                if (*FileName == '*')
                {
                    FillChar = '?';
                    break;
                }
 
                Fcb->FileExt[i++] = RtlUpperChar(*FileName++);
            }
 
            /* Fill the whole field with blanks only if bit 3 is not set */
            if ((FillChar != ' ') || (i != 0) || !(Options & (1 << 3)))
            {
                for (; i < 3; i++) Fcb->FileExt[i] = FillChar;
            }
 
            break;
        }
 
        /* Get System Date */
        case 0x2A:
        {
            GetLocalTime(&SystemTime);
            setCX(SystemTime.wYear);
            setDX(MAKEWORD(SystemTime.wDay, SystemTime.wMonth));
            setAL(SystemTime.wDayOfWeek);
            break;
        }
 
        /* Set System Date */
        case 0x2B:
        {
            GetLocalTime(&SystemTime);
            SystemTime.wYear  = getCX();
            SystemTime.wMonth = getDH();
            SystemTime.wDay   = getDL();
 
            /* Return success or failure */
            setAL(SetLocalTime(&SystemTime) ? 0x00 : 0xFF);
            break;
        }
 
        /* Get System Time */
        case 0x2C:
        {
            GetLocalTime(&SystemTime);
            setCX(MAKEWORD(SystemTime.wMinute, SystemTime.wHour));
            setDX(MAKEWORD(SystemTime.wMilliseconds / 10, SystemTime.wSecond));
            break;
        }
 
        /* Set System Time */
        case 0x2D:
        {
            GetLocalTime(&SystemTime);
            SystemTime.wHour         = getCH();
            SystemTime.wMinute       = getCL();
            SystemTime.wSecond       = getDH();
            SystemTime.wMilliseconds = getDL() * 10; // In hundredths of seconds
 
            /* Return success or failure */
            setAL(SetLocalTime(&SystemTime) ? 0x00 : 0xFF);
            break;
        }
 
        /* Get Disk Transfer Area */
        case 0x2F:
        {
            setES(HIWORD(Sda->DiskTransferArea));
            setBX(LOWORD(Sda->DiskTransferArea));
            break;
        }
 
        /* Get DOS Version */
        case 0x30:
        {
            PDOS_PSP PspBlock = SEGMENT_TO_PSP(Sda->CurrentPsp);
 
            /*
             * DOS 2+ - GET DOS VERSION
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2711.htm
             * for more information.
             */
 
            if (LOBYTE(PspBlock->DosVersion) < 5 || getAL() == 0x00)
            {
                /*
                 * Return DOS OEM number:
                 * 0x00 for IBM PC-DOS
                 * 0x02 for packaged MS-DOS
                 * 0xFF for NT DOS
                 */
                setBH(0xFF);
            }
 
            if (LOBYTE(PspBlock->DosVersion) >= 5 && getAL() == 0x01)
            {
                /*
                 * Return version flag:
                 * 1 << 3 if DOS is in ROM,
                 * 0 (reserved) if not.
                 */
                setBH(0x00);
            }
 
            /* Return DOS 24-bit user serial number in BL:CX */
            setBL(0x00);
            setCX(0x0000);
 
            /*
             * Return DOS version: Minor:Major in AH:AL
             * The Windows NT DOS box returns version 5.00, subject to SETVER.
             */
            setAX(PspBlock->DosVersion);
 
            break;
        }
 
        /* Terminate and Stay Resident */
        case 0x31:
        {
            DPRINT1("Process going resident: %u paragraphs kept\n", getDX());
            DosTerminateProcess(Sda->CurrentPsp, getAL(), getDX());
            break;
        }
 
        /* Extended functionalities */
        case 0x33:
        {
            switch (getAL())
            {
                /*
                 * DOS 4+ - GET BOOT DRIVE
                 */
                case 0x05:
                {
                    setDL(SysVars->BootDrive);
                    break;
                }
 
                /*
                 * DOS 5+ - GET TRUE VERSION NUMBER
                 * This function always returns the true version number, unlike
                 * AH=30h, whose return value may be changed with SETVER.
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2730.htm
                 * for more information.
                 */
                case 0x06:
                {
                    /*
                     * Return the true DOS version: Minor:Major in BH:BL
                     * The Windows NT DOS box returns BX=3205h (version 5.50).
                     */
                    setBX(NTDOS_VERSION);
 
                    /* DOS revision 0 */
                    setDL(0x00);
 
                    /* Unpatched DOS */
                    setDH(0x00);
 
                    break;
                }
 
                default: // goto Default;
                {
                    DPRINT1("INT 21h, AH = %02Xh, subfunction AL = %02Xh NOT IMPLEMENTED\n",
                            getAH(), getAL());
                }
            }
 
            break;
        }
 
        /* Get Address of InDOS flag */
        case 0x34:
        {
            setES(DOS_DATA_SEGMENT);
            setBX(DOS_DATA_OFFSET(Sda.InDos));
            break;
        }
 
        /* Get Interrupt Vector */
        case 0x35:
        {
            ULONG FarPointer = ((PULONG)BaseAddress)[getAL()];
 
            /* Read the address from the IDT into ES:BX */
            setES(HIWORD(FarPointer));
            setBX(LOWORD(FarPointer));
            break;
        }
 
        /* Get Free Disk Space */
        case 0x36:
        {
            CHAR RootPath[] = "?:\\";
            DWORD SectorsPerCluster;
            DWORD BytesPerSector;
            DWORD NumberOfFreeClusters;
            DWORD TotalNumberOfClusters;
 
            if (getDL() == 0x00)
                RootPath[0] = 'A' + Sda->CurrentDrive;
            else
                RootPath[0] = 'A' + getDL() - 1;
 
            if (GetDiskFreeSpaceA(RootPath,
                                  &SectorsPerCluster,
                                  &BytesPerSector,
                                  &NumberOfFreeClusters,
                                  &TotalNumberOfClusters))
            {
                setAX(LOWORD(SectorsPerCluster));
                setCX(LOWORD(BytesPerSector));
                setBX(min(NumberOfFreeClusters, 0xFFFF));
                setDX(min(TotalNumberOfClusters, 0xFFFF));
            }
            else
            {
                /* Error */
                setAX(0xFFFF);
            }
 
            break;
        }
 
        /* SWITCH character - AVAILDEV */
        case 0x37:
        {
            switch (getAL())
            {
                /*
                 * DOS 2+ - "SWITCHAR" - GET SWITCH CHARACTER
                 * This setting is ignored by MS-DOS 4.0+.
                 * MS-DOS 5+ always return AL=00h/DL=2Fh.
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2752.htm
                 * for more information.
                 */
                case 0x00:
                    setDL('/');
                    setAL(0x00);
                    break;
 
                /*
                 * DOS 2+ - "SWITCHAR" - SET SWITCH CHARACTER
                 * This setting is ignored by MS-DOS 5+.
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2753.htm
                 * for more information.
                 */
                case 0x01:
                    // getDL();
                    setAL(0xFF);
                    break;
 
                /*
                 * DOS 2.x and 3.3+ only - "AVAILDEV" - SPECIFY \DEV\ PREFIX USE
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2754.htm
                 * for more information.
                 */
                case 0x02:
                    // setDL();
                    setAL(0xFF);
                    break;
 
                /*
                 * DOS 2.x and 3.3+ only - "AVAILDEV" - SPECIFY \DEV\ PREFIX USE
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2754.htm
                 * for more information.
                 */
                case 0x03:
                    // getDL();
                    setAL(0xFF);
                    break;
 
                /* Invalid subfunction */
                default:
                    setAL(0xFF);
                    break;
            }
 
            break;
        }
 
        /* Get/Set Country-dependent Information */
        case 0x38:
        {
            WORD CountryId = getAL() < 0xFF ? getAL() : getBX();
            WORD ErrorCode;
 
            ErrorCode = DosGetCountryInfo(&CountryId,
                                          (PDOS_COUNTRY_INFO)SEG_OFF_TO_PTR(getDS(), getDX()));
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setBX(CountryId);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Create Directory */
        case 0x39:
        {
            String = (PCHAR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            if (CreateDirectoryA(String, NULL))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(LOWORD(GetLastError()));
            }
 
            break;
        }
 
        /* Remove Directory */
        case 0x3A:
        {
            String = (PCHAR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            if (RemoveDirectoryA(String))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(LOWORD(GetLastError()));
            }
 
            break;
        }
 
        /* Set Current Directory */
        case 0x3B:
        {
            String = (PCHAR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            if (DosChangeDirectory(String))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
            }
 
            break;
        }
 
        /* Create or Truncate File */
        case 0x3C:
        {
            WORD FileHandle;
            WORD ErrorCode = DosCreateFile(&FileHandle,
                                           (LPCSTR)SEG_OFF_TO_PTR(getDS(), getDX()),
                                           CREATE_ALWAYS,
                                           getCX());
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(FileHandle);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Open File or Device */
        case 0x3D:
        {
            WORD FileHandle;
            BYTE AccessShareModes = getAL();
            LPCSTR FileName = (LPCSTR)SEG_OFF_TO_PTR(getDS(), getDX());
            WORD ErrorCode = DosOpenFile(&FileHandle, FileName, AccessShareModes);
 
            /*
             * Check if we failed because we attempted to open a file for write
             * on a CDROM drive. In that situation, attempt to reopen for read
             */
            if (ErrorCode == ERROR_ACCESS_DENIED &&
                (AccessShareModes & 0x03) != 0 && DosIsFileOnCdRom())
            {
                ErrorCode = DosOpenFile(&FileHandle, FileName, 0);
            }
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(FileHandle);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Close File or Device */
        case 0x3E:
        {
            if (DosCloseHandle(getBX()))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_HANDLE);
            }
 
            break;
        }
 
        /* Read from File or Device */
        case 0x3F:
        {
            WORD BytesRead = 0;
            WORD ErrorCode;
 
            DPRINT("DosReadFile(0x%04X)\n", getBX());
 
            ErrorCode = DosReadFile(getBX(),
                                    MAKELONG(getDX(), getDS()),
                                    getCX(),
                                    &BytesRead);
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(BytesRead);
            }
            else if (ErrorCode != ERROR_NOT_READY)
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Write to File or Device */
        case 0x40:
        {
            WORD BytesWritten = 0;
            WORD ErrorCode = DosWriteFile(getBX(),
                                          MAKELONG(getDX(), getDS()),
                                          getCX(),
                                          &BytesWritten);
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(BytesWritten);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Delete File */
        case 0x41:
        {
            LPSTR FileName = (LPSTR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            if (demFileDelete(FileName) == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                /*
                 * See Ralf Brown: http://www.ctyme.com/intr/rb-2797.htm
                 * "AX destroyed (DOS 3.3) AL seems to be drive of deleted file."
                 */
                setAL(RtlUpperChar(FileName[0]) - 'A');
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(GetLastError());
            }
 
            break;
        }
 
        /* Seek File */
        case 0x42:
        {
            DWORD NewLocation;
            WORD ErrorCode = DosSeekFile(getBX(),
                                         MAKELONG(getDX(), getCX()),
                                         getAL(),
                                         &NewLocation);
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
 
                /* Return the new offset in DX:AX */
                setDX(HIWORD(NewLocation));
                setAX(LOWORD(NewLocation));
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Get/Set File Attributes */
        case 0x43:
        {
            DWORD Attributes;
            LPSTR FileName = (LPSTR)SEG_OFF_TO_PTR(getDS(), getDX());
 
            if (getAL() == 0x00)
            {
                /* Get the attributes */
                Attributes = GetFileAttributesA(FileName);
 
                /* Check if it failed */
                if (Attributes == INVALID_FILE_ATTRIBUTES)
                {
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                    setAX(GetLastError());
                }
                else
                {
                    /* Return the attributes that DOS can understand */
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    setCX(Attributes & 0x00FF);
                }
            }
            else if (getAL() == 0x01)
            {
                /* Try to set the attributes */
                if (SetFileAttributesA(FileName, getCL()))
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                }
                else
                {
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                    setAX(GetLastError());
                }
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_FUNCTION);
            }
 
            break;
        }
 
        /* IOCTL */
        case 0x44:
        {
            WORD Length = getCX();
 
            if (DosDeviceIoControl(getBX(), getAL(), MAKELONG(getDX(), getDS()), &Length))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(Length);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
            }
 
            break;
        }
 
        /* Duplicate Handle */
        case 0x45:
        {
            WORD NewHandle = DosDuplicateHandle(getBX());
 
            if (NewHandle != INVALID_DOS_HANDLE)
            {
                setAX(NewHandle);
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
            }
 
            break;
        }
 
        /* Force Duplicate Handle */
        case 0x46:
        {
            if (DosForceDuplicateHandle(getBX(), getCX()))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_HANDLE);
            }
 
            break;
        }
 
        /* Get Current Directory */
        case 0x47:
        {
            BYTE DriveNumber = getDL();
            String = (PCHAR)SEG_OFF_TO_PTR(getDS(), getSI());
 
            /* Get the real drive number */
            if (DriveNumber == 0)
            {
                DriveNumber = Sda->CurrentDrive;
            }
            else
            {
                /* Decrement DriveNumber since it was 1-based */
                DriveNumber--;
            }
 
            if (DriveNumber < SysVars->NumLocalDrives)
            {
                /*
                 * Copy the current directory into the target buffer.
                 * It doesn't contain the drive letter and the backslash.
                 */
                strncpy(String, DosData->CurrentDirectories[DriveNumber], DOS_DIR_LENGTH);
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(0x0100); // Undocumented, see Ralf Brown: http://www.ctyme.com/intr/rb-2933.htm
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_DRIVE);
            }
 
            break;
        }
 
        /* Allocate Memory */
        case 0x48:
        {
            WORD MaxAvailable = 0;
            WORD Segment = DosAllocateMemory(getBX(), &MaxAvailable);
 
            if (Segment != 0)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(Segment);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
                setBX(MaxAvailable);
            }
 
            break;
        }
 
        /* Free Memory */
        case 0x49:
        {
            if (DosFreeMemory(getES()))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
            }
 
            break;
        }
 
        /* Resize Memory Block */
        case 0x4A:
        {
            WORD Size;
 
            if (DosResizeMemory(getES(), getBX(), &Size))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
                setBX(Size);
            }
 
            break;
        }
 
        /* Execute */
        case 0x4B:
        {
            BYTE OrgAL = getAL();
            LPSTR ProgramName = SEG_OFF_TO_PTR(getDS(), getDX());
            PDOS_EXEC_PARAM_BLOCK ParamBlock = SEG_OFF_TO_PTR(getES(), getBX());
            WORD ErrorCode;
 
            if (OrgAL <= DOS_LOAD_OVERLAY)
            {
                DOS_EXEC_TYPE LoadType = (DOS_EXEC_TYPE)OrgAL;
 
                if (LoadType == DOS_LOAD_AND_EXECUTE)
                {
                    /* Create a new process */
                    ErrorCode = DosCreateProcess(ProgramName,
                                                 ParamBlock,
                                                 MAKELONG(Stack[STACK_IP], Stack[STACK_CS]));
                }
                else
                {
                    /* Just load an executable */
                    ErrorCode = DosLoadExecutable(LoadType,
                                                  ProgramName,
                                                  ParamBlock,
                                                  NULL,
                                                  NULL,
                                                  MAKELONG(Stack[STACK_IP], Stack[STACK_CS]));
                }
            }
            else if (OrgAL == 0x05)
            {
                // http://www.ctyme.com/intr/rb-2942.htm
                DPRINT1("Set execution state is UNIMPLEMENTED\n");
                ErrorCode = ERROR_CALL_NOT_IMPLEMENTED;
            }
            else
            {
                ErrorCode = ERROR_INVALID_FUNCTION;
            }
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Terminate with Return Code */
        case 0x4C:
        {
            DosTerminateProcess(Sda->CurrentPsp, getAL(), 0);
            break;
        }
 
        /* Get Return Code (ERRORLEVEL) */
        case 0x4D:
        {
            /*
             * According to Ralf Brown: http://www.ctyme.com/intr/rb-2976.htm
             * DosErrorLevel is cleared after being read by this function.
             */
            Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            setAX(Sda->ErrorLevel);
            Sda->ErrorLevel = 0x0000; // Clear it
            break;
        }
 
        /* Find First File */
        case 0x4E:
        {
            WORD Result = (WORD)demFileFindFirst(FAR_POINTER(Sda->DiskTransferArea),
                                                 SEG_OFF_TO_PTR(getDS(), getDX()),
                                                 getCX());
 
            setAX(Result);
 
            if (Result == ERROR_SUCCESS)
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            else
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
 
            break;
        }
 
        /* Find Next File */
        case 0x4F:
        {
            WORD Result = (WORD)demFileFindNext(FAR_POINTER(Sda->DiskTransferArea));
 
            setAX(Result);
 
            if (Result == ERROR_SUCCESS)
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            else
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
 
            break;
        }
 
        /* Internal - Set Current Process ID (Set PSP Address) */
        case 0x50:
        {
            DosSetProcessContext(getBX());
            break;
        }
 
        /* Internal - Get Current Process ID (Get PSP Address) */
        case 0x51:
        /* Get Current PSP Address */
        case 0x62:
        {
            /*
             * Undocumented AH=51h is identical to the documented AH=62h.
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2982.htm
             * and http://www.ctyme.com/intr/rb-3140.htm
             * for more information.
             */
            setBX(Sda->CurrentPsp);
            break;
        }
 
        /* Internal - Get "List of lists" (SYSVARS) */
        case 0x52:
        {
            /*
             * On return, ES points at the DOS data segment (see also INT 2F/AX=1203h).
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2983.htm
             * for more information.
             */
 
            /* Return the DOS "list of lists" in ES:BX */
            setES(DOS_DATA_SEGMENT);
            setBX(DOS_DATA_OFFSET(SysVars.FirstDpb));
            break;
        }
 
        /* Create Child PSP */
        case 0x55:
        {
            DosCreatePsp(getDX(), getSI());
            DosSetProcessContext(getDX());
            break;
        }
 
        /* Rename File */
        case 0x56:
        {
            LPSTR ExistingFileName = (LPSTR)SEG_OFF_TO_PTR(getDS(), getDX());
            LPSTR NewFileName      = (LPSTR)SEG_OFF_TO_PTR(getES(), getDI());
 
            /*
             * See Ralf Brown: http://www.ctyme.com/intr/rb-2990.htm
             * for more information.
             */
 
            if (MoveFileA(ExistingFileName, NewFileName))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(GetLastError());
            }
 
            break;
        }
 
        /* File Attributes */
        case 0x57:
        {
            switch (getAL())
            {
                /* Get File's last-written Date and Time */
                case 0x00:
                {
                    PDOS_FILE_DESCRIPTOR Descriptor = DosGetHandleFileDescriptor(getBX());
                    FILETIME LastWriteTime;
                    WORD FileDate, FileTime;
 
                    if (Descriptor == NULL)
                    {
                        /* Invalid handle */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        // Sda->LastErrorCode = ERROR_INVALID_HANDLE;
                        setAX(ERROR_INVALID_HANDLE);
                        break;
                    }
 
                    if (Descriptor->DeviceInfo & FILE_INFO_DEVICE)
                    {
                        /* Invalid for devices */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        // setAX(ERROR_INVALID_FUNCTION);
                        setAX(ERROR_INVALID_HANDLE);
                        break;
                    }
 
                    /*
                     * Retrieve the last-written Win32 date and time,
                     * and convert it to DOS format.
                     */
                    if (!GetFileTime(Descriptor->Win32Handle,
                                     NULL, NULL, &LastWriteTime) ||
                        !FileTimeToDosDateTime(&LastWriteTime,
                                               &FileDate, &FileTime))
                    {
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        setAX(GetLastError());
                        break;
                    }
 
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    setCX(FileTime);
                    setDX(FileDate);
                    break;
                }
 
                /* Set File's last-written Date and Time */
                case 0x01:
                {
                    PDOS_FILE_DESCRIPTOR Descriptor = DosGetHandleFileDescriptor(getBX());
                    FILETIME LastWriteTime;
                    WORD FileDate = getDX();
                    WORD FileTime = getCX();
 
                    if (Descriptor == NULL)
                    {
                        /* Invalid handle */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        // Sda->LastErrorCode = ERROR_INVALID_HANDLE;
                        setAX(ERROR_INVALID_HANDLE);
                        break;
                    }
 
                    if (Descriptor->DeviceInfo & FILE_INFO_DEVICE)
                    {
                        /* Invalid for devices */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        // setAX(ERROR_INVALID_FUNCTION);
                        setAX(ERROR_INVALID_HANDLE);
                        break;
                    }
 
                    /*
                     * Convert the new last-written DOS date and time
                     * to Win32 format and set it.
                     */
                    if (!DosDateTimeToFileTime(FileDate, FileTime,
                                               &LastWriteTime) ||
                        !SetFileTime(Descriptor->Win32Handle,
                                     NULL, NULL, &LastWriteTime))
                    {
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        setAX(GetLastError());
                        break;
                    }
 
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    break;
                }
 
                default: // goto Default;
                {
                    DPRINT1("INT 21h, AH = %02Xh, subfunction AL = %02Xh NOT IMPLEMENTED\n",
                            getAH(), getAL());
                }
            }
 
            break;
        }
 
        /* Get/Set Memory Management Options */
        case 0x58:
        {
            switch (getAL())
            {
                /* Get allocation strategy */
                case 0x00:
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    setAX(Sda->AllocStrategy);
                    break;
                }
 
                /* Set allocation strategy */
                case 0x01:
                {
                    if ((getBL() & (DOS_ALLOC_HIGH | DOS_ALLOC_HIGH_LOW))
                        == (DOS_ALLOC_HIGH | DOS_ALLOC_HIGH_LOW))
                    {
                        /* Can't set both */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        setAX(ERROR_INVALID_PARAMETER);
                        break;
                    }
 
                    if ((getBL() & ~(DOS_ALLOC_HIGH | DOS_ALLOC_HIGH_LOW))
                        > DOS_ALLOC_LAST_FIT)
                    {
                        /* Invalid allocation strategy */
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        setAX(ERROR_INVALID_PARAMETER);
                        break;
                    }
 
                    Sda->AllocStrategy = getBL();
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    break;
                }
 
                /* Get UMB link state */
                case 0x02:
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    setAL(SysVars->UmbLinked ? 0x01 : 0x00);
                    break;
                }
 
                /* Set UMB link state */
                case 0x03:
                {
                    BOOLEAN Success;
 
                    if (getBX())
                        Success = DosLinkUmb();
                    else
                        Success = DosUnlinkUmb();
 
                    if (Success)
                        Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    else
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
 
                    break;
                }
 
                /* Invalid or unsupported function */
                default:
                {
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                    setAX(ERROR_INVALID_FUNCTION);
                }
            }
 
            break;
        }
 
        /* Get Extended Error Information */
        case 0x59:
        {
            DPRINT1("INT 21h, AH = 59h, BX = %04Xh - Get Extended Error Information is UNIMPLEMENTED\n",
                    getBX());
            break;
        }
 
        /* Create Temporary File */
        case 0x5A:
        {
            LPSTR PathName = (LPSTR)SEG_OFF_TO_PTR(getDS(), getDX());
            LPSTR FileName = PathName; // The buffer for the path and the full file name is the same.
            UINT  uRetVal;
            WORD  FileHandle;
            WORD  ErrorCode;
 
            /*
             * See Ralf Brown: http://www.ctyme.com/intr/rb-3014.htm
             * for more information.
             */
 
            // FIXME: Check for buffer validity?
            // It should be a ASCIIZ path ending with a '\' + 13 zero bytes
            // to receive the generated filename.
 
            /* First create the temporary file */
            uRetVal = GetTempFileNameA(PathName, NULL, 0, FileName);
            if (uRetVal == 0)
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(GetLastError());
                break;
            }
 
            /* Now try to open it in read/write access */
            ErrorCode = DosOpenFile(&FileHandle, FileName, 2);
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(FileHandle);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Create New File */
        case 0x5B:
        {
            WORD FileHandle;
            WORD ErrorCode = DosCreateFile(&FileHandle,
                                           (LPCSTR)SEG_OFF_TO_PTR(getDS(), getDX()),
                                           CREATE_NEW,
                                           getCX());
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(FileHandle);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Lock/Unlock Region of File */
        case 0x5C:
        {
            if (getAL() == 0x00)
            {
                /* Lock region of file */
                if (DosLockFile(getBX(), MAKELONG(getDX(), getCX()), MAKELONG(getDI(), getSI())))
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                }
                else
                {
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                    setAX(Sda->LastErrorCode);
                }
            }
            else if (getAL() == 0x01)
            {
                /* Unlock region of file */
                if (DosUnlockFile(getBX(), MAKELONG(getDX(), getCX()), MAKELONG(getDI(), getSI())))
                {
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                }
                else
                {
                    Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                    setAX(Sda->LastErrorCode);
                }
            }
            else
            {
                /* Invalid subfunction */
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_FUNCTION);
            }
 
            break;
        }
 
        /* Canonicalize File Name or Path */
        case 0x60:
        {
            /*
             * See Ralf Brown: http://www.ctyme.com/intr/rb-3137.htm
             * for more information.
             */
 
            /*
             * We suppose that the DOS app gave to us a valid
             * 128-byte long buffer for the canonicalized name.
             */
            DWORD dwRetVal = GetFullPathNameA(SEG_OFF_TO_PTR(getDS(), getSI()),
                                              128,
                                              SEG_OFF_TO_PTR(getES(), getDI()),
                                              NULL);
            if (dwRetVal == 0)
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(GetLastError());
            }
            else
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setAX(0x0000);
            }
 
            // FIXME: Convert the full path name into short version.
            // We cannot reliably use GetShortPathName, because it fails
            // if the path name given doesn't exist. However this DOS
            // function AH=60h should be able to work even for non-existing
            // path and file names.
 
            break;
        }
 
        /* Miscellaneous Internal Functions */
        case 0x5D:
        {
            switch (getAL())
            {
                /* Get Swappable Data Area */
                case 0x06:
                {
                    setDS(DOS_DATA_SEGMENT);
                    setSI(DOS_DATA_OFFSET(Sda.ErrorMode));
                    setCX(sizeof(DOS_SDA));
                    setDX(FIELD_OFFSET(DOS_SDA, LastAX));
 
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    break;
                }
 
                default: // goto Default;
                {
                    DPRINT1("INT 21h, AH = %02Xh, subfunction AL = %02Xh NOT IMPLEMENTED\n",
                            getAH(), getAL());
                }
            }
 
            break;
        }
 
        /* Extended Country Information */
        case 0x65:
        {
            switch (getAL())
            {
                case 0x01: case 0x02: case 0x03:
                case 0x04: case 0x05: case 0x06:
                case 0x07:
                {
                    WORD BufferSize = getCX();
                    WORD ErrorCode;
                    ErrorCode = DosGetCountryInfoEx(getAL(),
                                                    getBX(),
                                                    getDX(),
                                                    (PDOS_COUNTRY_INFO_2)SEG_OFF_TO_PTR(getES(), getDI()),
                                                    &BufferSize);
                    if (ErrorCode == ERROR_SUCCESS)
                    {
                        Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                        setCX(BufferSize);
                    }
                    else
                    {
                        Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                        setAX(ErrorCode);
                    }
 
                    break;
                }
 
                /* Country-dependent Character Capitalization -- Character */
                case 0x20:
                /* Country-dependent Filename Capitalization -- Character */
                case 0xA0:
                {
                    setDL(DosToUpper(getDL()));
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    // setAX(ERROR_SUCCESS);
                    break;
                }
 
                /* Country-dependent Character Capitalization -- Counted ASCII String */
                case 0x21:
                /* Country-dependent Filename Capitalization -- Counted ASCII String */
                case 0xA1:
                {
                    PCHAR Str = (PCHAR)SEG_OFF_TO_PTR(getDS(), getDX());
                    // FIXME: Check for NULL ptr!!
                    DosToUpperStrN(Str, Str, getCX());
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    // setAX(ERROR_SUCCESS);
                    break;
                }
 
                /* Country-dependent Character Capitalization -- ASCIIZ String */
                case 0x22:
                /* Country-dependent Filename Capitalization -- ASCIIZ String */
                case 0xA2:
                {
                    PSTR Str = (PSTR)SEG_OFF_TO_PTR(getDS(), getDX());
                    // FIXME: Check for NULL ptr!!
                    DosToUpperStrZ(Str, Str);
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    // setAX(ERROR_SUCCESS);
                    break;
                }
 
                /* Determine if Character represents YES/NO Response */
                case 0x23:
                {
                    setAX(DosIfCharYesNo(MAKEWORD(getDL(), getDH())));
                    Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    break;
                }
 
                default: // goto Default;
                {
                    DPRINT1("INT 21h, AH = %02Xh, subfunction AL = %02Xh NOT IMPLEMENTED\n",
                            getAH(), getAL());
                }
            }
 
            break;
        }
 
        /* Set Handle Count */
        case 0x67:
        {
            if (!DosResizeHandleTable(getBX()))
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(Sda->LastErrorCode);
            }
            else Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
 
            break;
        }
 
        /* Commit File */
        case 0x68:
        case 0x6A:
        {
            /*
             * Function 6Ah is identical to function 68h,
             * and sets AH to 68h if success.
             * See Ralf Brown: http://www.ctyme.com/intr/rb-3176.htm
             * for more information.
             */
            setAH(0x68);
 
            if (DosFlushFileBuffers(getBX()))
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(GetLastError());
            }
 
            break;
        }
 
        /* Extended Open/Create */
        case 0x6C:
        {
            WORD FileHandle;
            WORD CreationStatus;
            WORD ErrorCode;
 
            /* Check for AL == 00 */
            if (getAL() != 0x00)
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ERROR_INVALID_FUNCTION);
                break;
            }
 
            /*
             * See Ralf Brown: http://www.ctyme.com/intr/rb-3179.htm
             * for the full detailed description.
             *
             * WARNING: BH contains some extended flags that are NOT SUPPORTED.
             */
 
            ErrorCode = DosCreateFileEx(&FileHandle,
                                        &CreationStatus,
                                        (LPCSTR)SEG_OFF_TO_PTR(getDS(), getSI()),
                                        getBL(),
                                        getDL(),
                                        getCX());
 
            if (ErrorCode == ERROR_SUCCESS)
            {
                Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                setCX(CreationStatus);
                setAX(FileHandle);
            }
            else
            {
                Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
                setAX(ErrorCode);
            }
 
            break;
        }
 
        /* Long FileName Support */
        case 0x71:
        {
            DPRINT1("INT 21h LFN Support, AH = %02Xh, AL = %02Xh NOT IMPLEMENTED!\n",
                    getAH(), getAL());
 
            setAL(0); // Some functions expect AL to be 0 when it's not supported.
            Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
            break;
        }
 
        /* Unsupported */
        default: // Default:
        {
            DPRINT1("DOS Function INT 21h, AH = %02Xh, AL = %02Xh NOT IMPLEMENTED!\n",
                    getAH(), getAL());
 
            setAL(0); // Some functions expect AL to be 0 when it's not supported.
            Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
        }
    }
 
    Sda->InDos--;
}

Referenced by DosInt21h(), and DosKRNLInitialize().

◆ DosInt27h()

VOID WINAPI DosInt27h ( LPWORD Stack )

Definition at line 2072 of file dos.c.

{
    WORD KeepResident = (getDX() + 0x0F) >> 4;
 
    /* Terminate and Stay Resident. CS must be the PSP segment. */
    DPRINT1("Process going resident: %u paragraphs kept\n", KeepResident);
    DosTerminateProcess(Stack[STACK_CS], 0, KeepResident);
}

Referenced by DosKRNLInitialize().

◆ DosInt2Ah()

VOID WINAPI DosInt2Ah ( LPWORD Stack )

Definition at line 2122 of file dos.c.

{
    DPRINT1("INT 2Ah, AX=%4xh called\n", getAX());
}

Referenced by DosKRNLInitialize().

◆ DosInt2Fh()

VOID WINAPI DosInt2Fh ( LPWORD Stack )

Definition at line 2127 of file dos.c.

{
    switch (getAH())
    {
        /* DOS 3+ Internal Utility Functions */
        case 0x12:
        {
            DPRINT1("INT 2Fh, AX=%4xh DOS Internal Utility Function called\n", getAX());
 
            switch (getAL())
            {
                /* Installation Check */
                case 0x00:
                {
                    setAL(0xFF);
                    break;
                }
 
                /* Get DOS Data Segment */
                case 0x03:
                {
                    setDS(DOS_DATA_SEGMENT);
                    break;
                }
 
                /* Compare FAR Pointers */
                case 0x14:
                {
                    PVOID PointerFromFarPointer1 = SEG_OFF_TO_PTR(getDS(), getSI());
                    PVOID PointerFromFarPointer2 = SEG_OFF_TO_PTR(getES(), getDI());
                    BOOLEAN AreEqual = (PointerFromFarPointer1 == PointerFromFarPointer2);
 
                    if (AreEqual)
                    {
                        Stack[STACK_FLAGS] |=  EMULATOR_FLAG_ZF;
                        Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_CF;
                    }
                    else
                    {
                        Stack[STACK_FLAGS] &= ~EMULATOR_FLAG_ZF;
                        Stack[STACK_FLAGS] |=  EMULATOR_FLAG_CF;
                    }
                    break;
                }
 
                /* Set DOS Version Number to return */
                case 0x2F:
                {
                    WORD DosVersion = getDX();
 
                    // Special case: return the true DOS version when DX=00h
                    if (DosVersion == 0x0000)
                        DosData->DosVersion = DOS_VERSION;
                    else
                        DosData->DosVersion = DosVersion;
 
                    break;
                }
            }
 
            break;
        }
 
        /* Set Disk Interrupt Handler */
        case 0x13:
        {
            /* Save the old values of PrevInt13 and RomBiosInt13 */
            ULONG OldInt13     = BiosData->PrevInt13;
            ULONG OldBiosInt13 = BiosData->RomBiosInt13;
 
            /* Set PrevInt13 and RomBiosInt13 to their new values */
            BiosData->PrevInt13    = MAKELONG(getDX(), getDS());
            BiosData->RomBiosInt13 = MAKELONG(getBX(), getES());
 
            /* Return in DS:DX the old value of PrevInt13 */
            setDS(HIWORD(OldInt13));
            setDX(LOWORD(OldInt13));
 
            /* Return in DS:DX the old value of RomBiosInt13 */
            setES(HIWORD(OldBiosInt13));
            setBX(LOWORD(OldBiosInt13));
 
            break;
        }
 
        /* Mostly Windows 2.x/3.x/9x support */
        case 0x16:
        {
            /*
             * AL=80h is DOS/Windows/DPMI "Release Current Virtual Machine Time-slice"
             * Just do nothing in this case.
             */
            if (getAL() != 0x80) goto Default;
            break;
        }
 
        /* Extended Memory Specification */
        case 0x43:
        {
            DWORD DriverEntry;
            if (!XmsGetDriverEntry(&DriverEntry)) break;
 
            switch (getAL())
            {
                /* Installation Check */
                case 0x00:
                {
                    /* The driver is loaded */
                    setAL(0x80);
                    break;
                }
 
                /* Get Driver Address */
                case 0x10:
                {
                    setES(HIWORD(DriverEntry));
                    setBX(LOWORD(DriverEntry));
                    break;
                }
 
                default:
                    DPRINT1("Unknown DOS XMS Function: INT 2Fh, AH = 43h, AL = %02Xh\n", getAL());
                    break;
            }
 
            break;
        }
 
        default: Default:
        {
            DPRINT1("DOS Internal System Function INT 2Fh, AH = %02Xh, AL = %02Xh NOT IMPLEMENTED!\n",
                    getAH(), getAL());
            Stack[STACK_FLAGS] |= EMULATOR_FLAG_CF;
        }
    }
}

Referenced by DosKRNLInitialize().

◆ DosIsFileOnCdRom()

static BOOLEAN DosIsFileOnCdRom ( VOID )

static

Definition at line 164 of file dos.c.

{
    UINT DriveType;
    CHAR RootPathName[4];
 
    /* Construct a simple <letter>:\ string to get drive type */
    RootPathName[0] = Sda->CurrentDrive + 'A';
    RootPathName[1] = ':';
    RootPathName[2] = '\\';
    RootPathName[3] = ANSI_NULL;
 
    DriveType = GetDriveTypeA(RootPathName);
    return (DriveType == DRIVE_CDROM);
}

Referenced by DosInt21h().

◆ DosKRNLInitialize()

BOOLEAN DosKRNLInitialize ( VOID )

Definition at line 2264 of file dos.c.

{
    UCHAR i;
    PDOS_SFT Sft;
    LPSTR Path;
    BOOLEAN Success = TRUE;
    DWORD dwRet;
    CHAR CurrentDirectory[MAX_PATH];
    CHAR DosDirectory[DOS_DIR_LENGTH];
 
    static const BYTE NullDriverRoutine[] =
    {
        /* Strategy routine entry */
        0x26, // mov [Request.Status], DOS_DEVSTAT_DONE
        0xC7,
        0x47,
        FIELD_OFFSET(DOS_REQUEST_HEADER, Status),
        LOBYTE(DOS_DEVSTAT_DONE),
        HIBYTE(DOS_DEVSTAT_DONE),
 
        /* Interrupt routine entry */
        0xCB, // retf
    };
 
    /* Set the data segment */
    setDS(DOS_DATA_SEGMENT);
 
    /* Initialize the global DOS data area */
    DosData = (PDOS_DATA)SEG_OFF_TO_PTR(DOS_DATA_SEGMENT, 0x0000);
    RtlZeroMemory(DosData, sizeof(*DosData));
 
    /* Initialize the DOS stack */
    setSS(DOS_DATA_SEGMENT);
    setSP(DOS_DATA_OFFSET(DosStack) + sizeof(DosData->DosStack) - sizeof(WORD));
 
    /* Initialize the list of lists */
    SysVars = &DosData->SysVars;
    RtlZeroMemory(SysVars, sizeof(*SysVars));
    SysVars->FirstSft = MAKELONG(DOS_DATA_OFFSET(Sft), DOS_DATA_SEGMENT);
    SysVars->CurrentDirs = MAKELONG(DOS_DATA_OFFSET(CurrentDirectories),
                                    DOS_DATA_SEGMENT);
    /*
     * The last drive can be redefined with the LASTDRIVE command.
     * At the moment, set the real maximum possible, 'Z'.
     */
    SysVars->NumLocalDrives = 'Z' - 'A' + 1; // See #define NUM_DRIVES in dos.h
 
    /* The boot drive is initialized to the %SYSTEMDRIVE% value */
    // NOTE: Using the NtSystemRoot system variable might be OS-specific...
    SysVars->BootDrive = RtlUpcaseUnicodeChar(SharedUserData->NtSystemRoot[0]) - 'A' + 1;
 
    /* Initialize the NUL device driver */
    SysVars->NullDevice.Link = MAXDWORD;
    SysVars->NullDevice.DeviceAttributes = DOS_DEVATTR_NUL | DOS_DEVATTR_CHARACTER;
    // Offset from within the DOS data segment
    SysVars->NullDevice.StrategyRoutine  = DOS_DATA_OFFSET(NullDriverRoutine);
    // Hardcoded to the RETF inside StrategyRoutine
    SysVars->NullDevice.InterruptRoutine = SysVars->NullDevice.StrategyRoutine + 6;
    RtlFillMemory(SysVars->NullDevice.DeviceName,
                  sizeof(SysVars->NullDevice.DeviceName),
                  ' ');
    RtlCopyMemory(SysVars->NullDevice.DeviceName, "NUL", strlen("NUL"));
    RtlCopyMemory(DosData->NullDriverRoutine,
                  NullDriverRoutine,
                  sizeof(NullDriverRoutine));
 
    /* Default DOS version to report */
    DosData->DosVersion = DOS_VERSION;
 
    /* Initialize the swappable data area */
    Sda = &DosData->Sda;
    RtlZeroMemory(Sda, sizeof(*Sda));
 
    /* Get the current directory and convert it to a DOS path */
    dwRet = GetCurrentDirectoryA(sizeof(CurrentDirectory), CurrentDirectory);
    if (dwRet == 0)
    {
        Success = FALSE;
        DPRINT1("GetCurrentDirectoryA failed (Error: %u)\n", GetLastError());
    }
    else if (dwRet > sizeof(CurrentDirectory))
    {
        Success = FALSE;
        DPRINT1("Current directory too long (%d > MAX_PATH) for GetCurrentDirectoryA\n", dwRet);
    }
 
    if (Success)
    {
        dwRet = GetShortPathNameA(CurrentDirectory, DosDirectory, sizeof(DosDirectory));
        if (dwRet == 0)
        {
            Success = FALSE;
            DPRINT1("GetShortPathNameA failed (Error: %u)\n", GetLastError());
        }
        else if (dwRet > sizeof(DosDirectory))
        {
            Success = FALSE;
            DPRINT1("Short path too long (%d > DOS_DIR_LENGTH) for GetShortPathNameA\n", dwRet);
        }
    }
 
    if (!Success)
    {
        /* We failed, use the boot drive instead */
        DosDirectory[0] = SysVars->BootDrive + 'A' - 1;
        DosDirectory[1] = ':';
        DosDirectory[2] = '\\';
        DosDirectory[3] = '\0';
    }
 
    /* Set the current drive */
    Sda->CurrentDrive = RtlUpperChar(DosDirectory[0]) - 'A';
 
    /* Get the directory part of the path and set the current directory */
    Path = strchr(DosDirectory, '\\');
    if (Path != NULL)
    {
        Path++; // Skip the backslash
        strncpy(DosData->CurrentDirectories[Sda->CurrentDrive], Path, DOS_DIR_LENGTH);
    }
    else
    {
        DosData->CurrentDirectories[Sda->CurrentDrive][0] = '\0';
    }
 
    /* Set the current PSP to the system PSP */
    Sda->CurrentPsp = SYSTEM_PSP;
 
    /* Initialize the SFT */
    Sft = (PDOS_SFT)FAR_POINTER(SysVars->FirstSft);
    Sft->Link = MAXDWORD;
    Sft->NumDescriptors = DOS_SFT_SIZE;
 
    for (i = 0; i < Sft->NumDescriptors; i++)
    {
        /* Clear the file descriptor entry */
        RtlZeroMemory(&Sft->FileDescriptors[i], sizeof(DOS_FILE_DESCRIPTOR));
    }
 
    /* Initialize memory management */
    DosInitializeMemory();
 
    /* Initialize the callback context */
    InitializeContext(&DosContext, DOS_CODE_SEGMENT, 0x0000);
 
    /* Register the DOS 32-bit Interrupts */
    RegisterDosInt32(0x20, DosInt20h        );
    RegisterDosInt32(0x21, DosInt21h        );
//  RegisterDosInt32(0x22, DosInt22h        ); // Termination
    RegisterDosInt32(0x23, DosBreakInterrupt); // Ctrl-C / Ctrl-Break
//  RegisterDosInt32(0x24, DosInt24h        ); // Critical Error
    RegisterDosInt32(0x25, DosAbsoluteRead  ); // Absolute Disk Read
    RegisterDosInt32(0x26, DosAbsoluteWrite ); // Absolute Disk Write
    RegisterDosInt32(0x27, DosInt27h        ); // Terminate and Stay Resident
    RegisterDosInt32(0x28, DosIdle          ); // DOS Idle Interrupt
    RegisterDosInt32(0x29, DosFastConOut    ); // DOS 2+ Fast Console Output
    RegisterDosInt32(0x2F, DosInt2Fh        ); // Multiplex Interrupt
 
    /* Unimplemented DOS interrupts */
    RegisterDosInt32(0x2A, DosInt2Ah); // DOS Critical Sections / Network
//  RegisterDosInt32(0x2E, NULL); // COMMAND.COM "Reload Transient"
//  COMMAND.COM adds support for INT 2Fh, AX=AE00h and AE01h "Installable Command - Installation Check & Execute"
//  COMMAND.COM adds support for INT 2Fh, AX=5500h "COMMAND.COM Interface"
 
    /* Reserved DOS interrupts */
    RegisterDosInt32(0x2B, NULL);
    RegisterDosInt32(0x2C, NULL);
    RegisterDosInt32(0x2D, NULL);
 
    /* Initialize country data */
    DosCountryInitialize();
 
    /* Load the CON driver */
    ConDrvInitialize();
 
    /* Load the XMS driver (HIMEM) */
    XmsInitialize();
 
    /* Load the EMS driver */
    if (!EmsDrvInitialize(EMS_SEGMENT, EMS_TOTAL_PAGES))
    {
        DosDisplayMessage("Could not initialize EMS. EMS will not be available.\n"
                          "Page frame segment or number of EMS pages invalid.\n");
    }
 
    /* Finally initialize the UMBs */
    DosInitializeUmb();
 
    return TRUE;
}