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Format of device driver request header

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Offset Size Description

00h

BYTE

length of request header

01h

BYTE

subunit within device driver

02h

BYTE

command code (see #02595)

03h

WORD

status (filled in by device driver) (see #02596)

---DOS---

05h

4 BYTEs

reserved (unused in DOS 2.x and 3.x)

09h

DWORD

(European MS-DOS 4.0 only) pointer to next request header in device's request queue

(other versions) reserved (unused in DOS 2.x and 3.x)

---STARLITE architecture---

05h

DWORD

pointer to next request header

09h

4 BYTEs

reserved

---command code 00h---

0Dh

BYTE

(ret) number of units

0Eh

DWORD

(call)

(European MS-DOS 4.0 only) pointer to DOS device helper function (see #02599)

(DOS 5+) pointer past end of memory available to driver

(ret) address of first free byte following driver

12h

DWORD

(call) pointer to commandline arguments
(ret) pointer to BPB array (block drivers) or 0000h:0000h (character drivers)

16h

BYTE

(DOS 3.0+) drive number for first unit of block driver (0=A)

---European MS-DOS 4.0---

17h

DWORD

pointer to function to save registers on stack

---DOS 5+ ---

17h

WORD

(ret) error-message flag
0001h MS-DOS should display error msg on init failure

---command code 01h---

0Dh

BYTE

media descriptor

0Eh

BYTE

(ret) media status
00h = don't know
01h = media has not changed
FFh = media has been changed

0Fh

DWORD

(ret) (DOS 3.0+) pointer to previous volume ID if the OPEN/CLOSE/RM bit in device header is set and disk changed
Note: Some drives (or controllers???) forget the change line status if another drive is accessed afterwards. The DOS IO.SYS layer takes care of this by not relying on the reported change line status when the change line is not active and a different drive is accessed, instead it reports "don't know" to the DOS kernel.

---command code 02h---

0Dh

BYTE

media descriptor

0Eh

DWORD

transfer address
scratch sector if NON-IBM FORMAT bit in device header set
first FAT sector otherwise

12h

DWORD

pointer to BPB (set by driver) (see #01663 at INT 21/AH=53h)

---command codes 03h, 0Ch---

(see also INT 21/AX=4402h"DOS 2+",INT 21/AX=4403h"DOS")

0Dh

BYTE

media descriptor (block devices only)

0Eh

DWORD

transfer address

12h

WORD

(call) number of bytes to read/write
(ret) actual number of bytes read or written

---command codes 04h, 08h, 09h (except Compaq DOS 3.31, DR DOS 6)---

0Dh

BYTE

media descriptor (block devices only)

0Eh

DWORD

transfer address

12h

WORD

byte count (character devices) or sector count (block devices)

14h

WORD

starting sector number (block devices only)

16h

DWORD

(DOS 3.0+) pointer to volume ID if error 0Fh returned

1Ah

DWORD

(DOS 4.0+) 32-bit starting sector number (block devices with device attribute word bit 1 set only) if starting sector number above is FFFFh (see INT 21/AH=52h)

---command codes 04h, 08h, 09h (Compaq DOS 3.31, DR DOS 6)---

0Dh

BYTE

media descriptor (block devices only)

0Eh

DWORD

transfer address

12h

WORD

byte count (character devices) or sector count (block devices)

14h

DWORD

32-bit starting sector number (block devices only)
Note: To reliably determine which variant of the request block for functions 04h,08h,09h has been passed to the driver, check the length field as well as the word at offset 14h. If the length is 1Eh and 14h=FFFFh, use the DWORD at 1Ah as the starting sector number; if the length is 18h, use the DWORD at 14h; otherwise, use the WORD at 14h.

---command code 05h---

0Dh

BYTE

byte read from device if BUSY bit clear on return

---command codes 06h, 07h, 0Ah, 0Bh, 0Dh, 0Eh, 0Fh---

no further fields

---command code 10h---

0Dh

BYTE

unused

0Eh

DWORD

transfer address

12h

WORD

(call) number of bytes to write
(ret) actual number of bytes written

---command codes 11h, 12h---

0Dh

BYTE

reserved

---command code 14h---

no further fields

Note: This is at least true for KKCFUNC.SYS' "device restore". KKCFUNC.SYS checks that INT 2Fh in the IVT still points to KKCFUNC's own INT 2Fh entry point. In this case it restores the original INT 2Fh vector, as recorded at device init, into the IVT.
See Also: INT 2F/AH=4Dh

---command code 15h---

no further fields

---command codes 13h, 19h---

0Dh

BYTE

category code
00h-7Fh = reserved for Microsoft
00h = unknown
01h = COMn: (serial) (DOS 3.3+)
02h = reserved for terminal control
03h = CON (DOS 3.3+)
04h = reserved for keyboard control
05h = LPTn:
07h = mouse (European MS-DOS 4.0)
08h = disk
48h = FAT32 disk control (MS-DOS 7.10+)
80h-FFh = reserved for OEM/user-defined
9Eh = (STARLITE) Media Access Control driver
EDh = (DR PalmDOS) login security
SeeAlso : #01558

0Eh

BYTE

function code
00h = (STARLITE) MAC Bind request

0Fh

WORD

copy of DS at time of IOCTL call (apparently unused in DOS 3.3)
SI contents (European MS-DOS 4.0)

11h

WORD

offset of device driver header (see #01646)
DI contents (European MS-DOS 4.0)

13h

DWORD

pointer to parameter block from INT 21/AX=440Ch or AX=440Dh

---command codes 80h, 82h---

0Dh

BYTE

addressing mode
00h = HSG (default)
01h = Phillips/Sony Red Book

0Eh

DWORD

transfer address (ignored for command 82h)

12h

WORD

number of sectors to read (if 0 for command 82h, request is an advisory seek)

14h

DWORD

starting sector number
logical sector number in HSG mode
frame/second/minute/unused in Red Book mode (HSG sector = minute * 4500 + second * 75 + frame - 150)

18h

BYTE

data read mode
00h = cooked (2048 bytes per frame)
01h = raw (2352 bytes per frame, including EDC/ECC)

19h

BYTE

interleave size (number of sectors stored consecutively)

1Ah

BYTE

interleave skip factor (number of sectors between consecutive portions)

---command code 83h---

0Dh

BYTE

addressing mode
00h = HSG (default)
01h = Phillips/Sony Red Book

0Eh

DWORD

transfer address (ignored)

12h

WORD

number of sectors to read (ignored)

14h

DWORD

starting sector number (see also above)

---command code 84h---

0Dh

BYTE

addressing mode
00h = HSG (default)
01h = Phillips/Sony Red Book

0Eh

DWORD

starting sector number (see also above)

12h

DWORD

number of sectors to play

---command codes 85h, 88h---

no further fields

---command codes 86h, 87h---

0Dh

BYTE

addressing mode
00h = HSG (default)
01h = Phillips/Sony Red Book

0Eh

DWORD

transfer address (ignored in write mode 0)

12h

WORD

number of sectors to write

14h

DWORD

starting sector number (also see above)

18h

BYTE

write mode
00h = mode 0 (write all zeros)
01h = mode 1 (default) (2048 bytes per sector)
02h = mode 2 form 1 (2048 bytes per sector)
03h = mode 2 form 2 (2336 bytes per sector)

19h

BYTE

interleave size (number of sectors stored consecutively)

1Ah

BYTE

interleave skip factor (number of sectors between consecutive portions)