INT 21 OU - DOS 4.x only internal - GET DOS SWAPPABLE DATA AREAS AX = 5D0Bh Return: CF set on error AX = error code (see AH=59h) CF clear if successful DS:SI -> swappable data area list (see below) Notes: copying and restoring the swappable data areas allows DOS to be reentered unless it is in a critical section delimited by calls to INT 2A/AH=80h and INT 2A/AH=81h,82h 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. DOS 5+ use the SDA format listed below, but revert back to the DOS 3.x call for finding the SDA (see AX=5D06h) SeeAlso: AX=5D06h,INT 2A/AH=80h,INT 2A/AH=81h,INT 2A/AH=82h,INT 2F/AX=1203h Format of DOS 4.x swappable data area list: Offset Size Description 00h WORD count of data areas 02h N BYTEs "count" copies of data area record Offset Size Description 00h DWORD address 04h WORD length and type bit 15 set if swap always, clear if swap in DOS bits 14-0: length in bytes Format of DOS 4.0-6.0 swappable data area: Offset Size Description -34 BYTE printer echo flag (00h off, FFh active) -31 BYTE current switch character (ignored by DOS 5+) -28 BYTE incremented on each INT 21/AX=5E01h call -27 16 BYTEs 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) (all offsets are 0D0Ch, but this list is still present for DOS 3.x compatibility) -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 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 18h BYTE flag: code page switching 19h BYTE flag: copy of previous byte in case of INT 24 Abort ---remainder need only be swapped if in DOS--- 1Ah WORD value of AX on call to INT 21 1Ch WORD PSP segment for sharing/network 1Eh WORD network machine number for sharing/network (0000h = us) 20h WORD first usable memory block found when allocating memory 22h WORD best usable memory block found when allocating memory 24h WORD last usable memory block found when allocating memory 26h WORD memory size in paragraphs (used only during initialization) 28h WORD last entry checked during directory search 2Ah BYTE flag: nonzero if INT 24 Fail 2Bh BYTE flags: allowable INT 24 responses (passed to INT 24 in AH) 2Ch BYTE flag: do not set directory if nonzero 2Dh BYTE flag: program aborted by ^C 2Eh BYTE flag: allow embedded blanks in FCB 2Fh BYTE padding (unused) 30h BYTE day of month 31h BYTE month 32h WORD year - 1980 34h WORD number of days since 1-1-1980 36h BYTE day of week (0 = Sunday) 37h BYTE flag: console swapped during read from device 38h BYTE flag: safe to call INT 28 if nonzero 39h BYTE flag: abort currently in progress, turn INT 24 Abort into Fail 3Ah 30 BYTEs device driver request header (see INT 2F/AX=0802h) for device calls 58h DWORD pointer to device driver entry point (used in calling driver) 5Ch 22 BYTEs device driver request header for I/O calls 72h 14 BYTEs device driver request header for disk status check 80h DWORD pointer to device I/O buffer 84h WORD ??? 86h WORD ??? (0) 88h BYTE type of PSP copy (00h=simple for INT 21/AH=26h, FFh=make child) 89h DWORD start offset of file region to lock/unlock 8Dh DWORD length of file region to lock/unlock 91h BYTE padding (unused) 92h 3 BYTEs 24-bit user number (see AH=30h) 95h BYTE OEM number (see AH=30h) 96h 6 BYTEs CLOCK$ transfer record (see AH=52h) 9Ch BYTE device I/O buffer for single-byte I/O functions??? 9Dh BYTE padding??? 9Eh 128 BYTEs buffer for filename 11Eh 128 BYTEs buffer for filename 19Eh 21 BYTEs findfirst/findnext search data block (see AH=4Eh) 1B3h 32 BYTEs directory entry for found file (see AH=11h) 1D3h 88 BYTEs copy of current directory structure for drive being accessed 22Bh 11 BYTEs FCB-format filename for device name comparison 236h BYTE terminating NUL for above filename 237h 11 BYTEs wildcard destination specification for rename (FCB format) 242h BYTE terminating NUL for above spec 243h BYTE ??? 244h WORD ??? 246h 5 BYTEs ??? 24Bh BYTE extended FCB file attributes 24Ch BYTE type of FCB (00h regular, FFh extended) 24Dh BYTE directory search attributes 24Eh BYTE file open/access mode 24Fh BYTE ??? flag bits 250h BYTE flag: device name found on rename, or file not found 251h BYTE splice flag??? (file name and directory name together) 252h BYTE flag indicating how DOS function was invoked (00h = direct INT 20/INT 21, FFh = server call AX=5D00h) 253h BYTE ??? 254h BYTE ??? 255h BYTE ??? 256h BYTE ??? 257h BYTE ??? 258h BYTE ??? 259h BYTE ??? 25Ah BYTE canonicalized filename referred to existing file/dir if FFh 25Bh BYTE ??? 25Ch BYTE type of process termination (00h-03h) 25Dh BYTE ??? 25Eh BYTE ??? 25Fh BYTE ??? 260h DWORD pointer to Drive Parameter Block for critical error invocation 264h DWORD pointer to stack frame containing user registers on INT 21 268h WORD stores SP??? 26Ah DWORD pointer to DOS Drive Parameter Block for ??? 26Eh WORD segment of disk buffer 270h WORD ??? 272h WORD ??? 274h WORD ??? 276h WORD ??? 278h BYTE Media ID byte returned by AH=1Bh,1Ch 279h BYTE ??? (doesn't seem to be referenced) 27Ah DWORD pointer to ??? 27Eh DWORD pointer to current SFT 282h DWORD pointer to current directory structure for drive being accessed 286h DWORD pointer to caller's FCB 28Ah WORD SFT index to which file being opened will refer 28Ch WORD temporary storage for file handle 28Eh DWORD pointer to a JFT entry in process handle table (see AH=26h) 292h WORD offset in DOS DS of first filename argument 294h WORD offset in DOS DS of second filename argument 296h WORD ??? 298h WORD ??? 29Ah WORD ??? 29Ch WORD ??? 29Eh WORD ??? 2A0h WORD ??? 2A2h WORD ??? directory cluster number??? 2A4h DWORD ??? 2A8h DWORD ??? 2ACh WORD ??? 2AEh DWORD offset in file??? 2B2h WORD ??? 2B4h WORD bytes in partial sector 2B6h WORD number of sectors 2B8h WORD ??? 2BAh WORD ??? 2BCh WORD ??? 2BEh DWORD number of bytes appended to file 2C2h DWORD pointer to ??? disk buffer 2C6h DWORD pointer to ??? SFT 2CAh WORD used by INT 21 dispatcher to store caller's BX 2CCh WORD used by INT 21 dispatcher to store caller's DS 2CEh WORD temporary storage while saving/restoring caller's registers 2D0h DWORD pointer to prev call frame (offset 264h) if INT 21 reentered also switched to for duration of INT 24 2D4h WORD open mode/action for INT 21/AX=6C00h 2D6h BYTE ??? (set to 00h by INT 21h dispatcher, 02h when a read is performed, and 01h or 03h by INT 21/AX=6C00h) 2D7h WORD ??? apparently unused 2D9h DWORD stored ES:DI for AX=6C00h 2DDh WORD extended file open action code (see AX=6C00h) 2DFh WORD extended file open attributes (see AX=6C00h) 2E1h WORD extended file open file mode (see AX=6C00h) 2E3h DWORD pointer to filename to open (see AX=6C00h) 2E7h WORD ??? 2E9h WORD ??? 2EBh BYTE ??? 2ECh WORD stores DS during call to [List-of-Lists + 37h] 2EEh WORD ??? 2F0h BYTE ??? 2F1h WORD ??? bit flags 2F3h DWORD pointer to user-supplied filename 2F7h DWORD pointer to ??? 2FBh WORD stores SS during call to [List-of-Lists + 37h] 2FDh WORD stores SP during call to [List-of-Lists + 37h] 2FFh BYTE flag, nonzero if stack switched in calling [List-of-Lists+37h] 300h 21 BYTEs FindFirst search data for source file(s) of a rename operation (see AH=4Eh) 315h 32 BYTEs directory entry for file being renamed (see AH=11h) 335h 331 BYTEs critical error stack 480h 384 BYTEs disk stack (functions greater than 0Ch, INT 25,INT 26) 600h 384 BYTEs character I/O stack (functions 01h through 0Ch) 780h BYTE device driver lookahead flag (usually printer) (see AH=64h) 781h BYTE volume change flag 782h BYTE flag: virtual open 783h BYTE ??? 784h WORD ??? 786h WORD ??? 788h WORD ??? 78Ah WORD ??? .