Int 21 Fn 5D06  U - DOS 3.0+ Internal - Get Address Of Dos Swappable Data  [D]

   AX = 5D06h

Return: CF set on error
      AX = error code (see AH=59h)
   CF clear if successful
       DS:SI -> nonreentrant data area (includes all three DOS stacks)
       (critical error flag is first byte)
       CX = size in bytes of area which must be swapped while in DOS
       DX = size in bytes of area which must always be swapped

Notes: the Critical Error flag is used in conjunction with the InDOS flag
     (see AH=34h) to determine when it is safe to enter DOS from a TSR
   setting CritErr flag allows use of functions 50h/51h from INT 28h under
     DOS 2.x by forcing use of correct stack
   swapping the data area allows reentering DOS unless DOS is in a
     critical section delimited by INT 2A/AH=80h and INT 2A/AH=81h,82h
   under DOS 4.0, AX=5D0Bh should be used instead of this function
   SHARE and other DOS utilities consult the byte at offset 04h in the
     DOS data segment (see INT 2F/AX=1203h) to determine the SDA format
     in use: 00h = DOS 3.x, 01h = DOS 4.0-6.0, other = error.
   DR-DOS 3.41+ supports this function, but the SDA format beyond the
     first 18h bytes is completely different from MS-DOS

See Also: AX=5D0Bh,INT 2A/AH=80h,INT 2A/AH=81h,INT 2A/AH=82h

Format of DOS 3.10-3.30 Swappable Data Area:
Offset Size    Description
 -34   BYTE    (DOS 3.10+) printer echo flag (00h off, FFh active)
 -31   BYTE    (DOS 3.30) current switch character
 -28   BYTE    (DOS 3.30) incremented on each INT 21/AX=5E01h call
 -27 16 BYTEs  (DOS 3.30) machine name set by INT 21/AX=5E01h
 -11  5 WORDs  zero-terminated list of offsets which need to be patched to
       enable critical-section calls (see INT 2A/AH=80h)
 -1    BYTE    unused padding
---start of actual SDA---
 00h   BYTE    critical error flag ("ErrorMode")
 01h   BYTE    InDOS flag (count of active INT 21 calls)
 02h   BYTE    drive on which current critical error occurred, or FFh
       (DR-DOS sets to drive number during INT 24, 00h otherwise)
 03h   BYTE    locus of last error
 04h   WORD    extended error code of last error
 06h   BYTE    suggested action for last error
 07h   BYTE    class of last error
 08h   DWORD   ES:DI pointer for last error
 0Ch   DWORD   current DTA
 10h   WORD    current PSP
 12h   WORD    stores SP across an INT 23
 14h   WORD    return code from last process termination (zerod after reading
       with AH=4Dh)
 16h   BYTE    current drive
 17h   BYTE    extended break flag
---remainder need only be swapped if in DOS---
 18h   WORD    value of AX on call to INT 21
 1Ah   WORD    PSP segment for sharing/network
 1Ch   WORD    network machine number for sharing/network (0000h = us)
 1Eh   WORD    first usable memory block found when allocating memory
 20h   WORD    best usable memory block found when allocating memory
 22h   WORD    last usable memory block found when allocating memory
 24h   WORD    memory size in paragraphs (used only during initialization)
 26h   WORD    last entry checked during directory search
 28h   BYTE    flag: INT 24 returned Fail
 29h   BYTE    flags: allowable INT 24 actions (passed to INT 24 in AH)
 2Ah   BYTE    directory flag (00h directory, 01h file)
 2Bh   BYTE    flag: FFh if Ctrl-Break termination, 00h otherwise
 2Ch   BYTE    flag: allow embedded blanks in FCB
 2Dh   BYTE    padding (unused)
 2Eh   BYTE    day of month
 2Fh   BYTE    month
 30h   WORD    year - 1980
 32h   WORD    number of days since 1-1-1980
 34h   BYTE    day of week (0 = Sunday)
 35h   BYTE    flag: console swapped during read from device
 36h   BYTE    flag: safe to call INT 28 if nonzero
 37h   BYTE    flag: if nonzero, INT 24 Abort turned into INT 24 Fail
       (set only during process termination)
 38h 26 BYTEs  device driver request header (see INT 2F/AX=0802h)
 52h   DWORD   pointer to device driver entry point (used in calling driver)
 56h 22 BYTEs  device driver request header for I/O calls
 6Ch 14 BYTEs  device driver request header for disk status check
 7Ah   DWORD   pointer to device I/O buffer???
 7Eh   WORD    ???
 80h   WORD    ???
 82h   BYTE    type of PSP copy (00h=simple for INT 21/AH=26h, FFh=make child)
 83h   BYTE    padding (unused)
 84h  3 BYTEs  24-bit user number (see AH=30h)
 87h   BYTE    OEM number (see AH=30h)
 88h   WORD    offset to error code conversion table for INT 25/INT 26
 8Ah  6 BYTEs  CLOCK$ transfer record (see AH=52h)
 90h   BYTE    device I/O buffer for single-byte I/O functions
 91h   BYTE    padding??? (unused)
 92h 128 BYTEs buffer for filename
112h 128 BYTEs buffer for filename
192h 21 BYTEs  findfirst/findnext search data block (see AH=4Eh)
1A7h 32 BYTEs  directory entry for found file (see AH=11h)
1C7h 81 BYTEs  copy of current directory structure for drive being accessed
218h 11 BYTEs  FCB-format filename for device name comparison
223h   BYTE    terminating NUL for above filename
224h 11 BYTEs  wildcard destination specification for rename (FCB format)
22Fh   BYTE    terminating NUL for above spec
230h   BYTE    ???
231h   WORD    destination file/directory starting sector
233h  5 BYTEs  ???
238h   BYTE    extended FCB file attribute
239h   BYTE    type of FCB (00h regular, FFh extended)
23Ah   BYTE    directory search attributes
23Bh   BYTE    file open/access mode
23Ch   BYTE    file found/delete flag
       bit 0: file found
       bit 4: file deleted
23Dh   BYTE    flag: device name found on rename, or file not found
23Eh   BYTE    splice flag (file name and directory name together)
23Fh   BYTE    flag indicating how DOS function was invoked
       (00h = direct INT 20/INT 21, FFh = server call AX=5D00h)
240h   BYTE    sector position within cluster
241h   BYTE    flag: translate sector/cluster (00h no, 01h yes)
242h   BYTE    flag: 00h if read, 01h if write
243h   BYTE    current working drive number
244h   BYTE    cluster factor
245h   BYTE    flag: cluster split mode
246h   BYTE    line edit (AH=0Ah) insert mode flag (nonzero = on)
247h   BYTE    canonicalized filename referred to existing file/dir if FFh
248h   BYTE    volume ID flag
249h   BYTE    type of process termination (00h-03h) (see AH=4Dh)
24Ah   BYTE    file create flag (00h = no)
24Bh   BYTE    value with which to replace first byte of deleted file's name
       (normally E5h, but 00h as described under INT 21/AH=13h)
24Ch   DWORD   pointer to Drive Parameter Block for critical error invocation
       temp: used during process termination
250h   DWORD   pointer to stack frame containing user registers on INT 21
254h   WORD    stores SP across INT 24
256h   DWORD   pointer to DOS Drive Parameter Block for ???
25Ah   WORD    saving partial cluster number
25Ch   WORD    temp: sector of work current cluster
25Eh   WORD    high part of cluster number (only low byte referenced)
260h   WORD    ??? temp
262h   BYTE    Media ID byte returned by AH=1Bh,1Ch
263h   BYTE    padding (unused)
264h   DWORD   pointer to device header
268h   DWORD   pointer to current SFT
26Ch   DWORD   pointer to current directory structure for drive being accessed
270h   DWORD   pointer to caller's FCB
274h   WORD    number of SFT to which file being opened will refer
276h   WORD    temporary storage for file handle
278h   DWORD   pointer to a JFT entry in process handle table (see AH=26h)
27Ch   WORD    offset in DOS DS of first filename argument
27Eh   WORD    offset in DOS DS of second filename argument
280h   WORD    offset of last component in pathname or FFFFh
282h   WORD    offset of transfer address to add
284h   WORD    last relative cluster within file being accessed
286h   WORD    temp: absolute cluster number being accessed
288h   WORD    directory sector number
28Ah   WORD    ??? current cluster number
28Ch   WORD    ??? current offset in file DIV bytes per sector
28Eh   WORD    current sector number
290h   WORD    current byte offset within sector
292h   DWORD   current offset in file
296h   DWORD   temp: file byte count
29Ah   WORD    temp: file byte count
29Ch   WORD    free file cluster entry
29Eh   WORD    last file cluster entry
2A0h   WORD    next file cluster number
2A2h   DWORD   number of bytes appended to file
2A6h   DWORD   pointer to current work disk buffer
2AAh   DWORD   pointer to working SFT
2AEh   WORD    used by INT 21 dispatcher to store caller's BX
2B0h   WORD    used by INT 21 dispatcher to store caller's DS
2B2h   WORD    temporary storage while saving/restoring caller's registers
2B4h   DWORD   pointer to prev call frame (offset 250h) if INT 21 reentered
       also switched to for duration of INT 24
2B8h 21 BYTEs  FindFirst search data for source file(s) of a rename operation
       (see AH=4Eh)
2CDh 32 BYTEs  directory entry for file being renamed (see AH=11h for format)
2EDh 331 BYTEs critical error stack
   403h     35 BYTEs scratch SFT
438h 384 BYTEs disk stack (functions greater than 0Ch, INT 25,INT 26)
5B8h 384 BYTEs character I/O stack (functions 01h through 0Ch)
---DOS 3.2,3.3x only---
738h   BYTE    device driver lookahead flag (usually printer) (see AH=64h)
739h   BYTE    volume change flag
73Ah   BYTE    flag: virtual open
73Bh   BYTE    ???