name driver
page 55,132
title''DRIVER --- installable driver template''
;
; This is a "template" for a MS-DOS installable device driver.
; The actual driver subroutines are stubs only and have
; No effect but to return a non-error "done" status.
;
; Ray Duncan
; Laboratory Microsystems Inc.
; April 1985
code segment public''CODE''
driver proc far
assume cs: code, ds: code, es: code
org 0
Max_Cmd equ 15; MS-DOS command code maximum
; This is 15 for MS-DOS 3.x
; And 12 for MS-DOS 2.x
cr equ 0dh; ASCII carriage return
lf equ 0ah; ASCII line feed
eom equ''$''; end of message signal
page
;
; Device Driver Header
;
Header dd -1; link to next device, -1 = end of list
dw 8000h; attribute word
; Bit 15 = 1 for character devices
dw Strat; device "Strategy" entry point
dw Intr; device "Interrupt" entry point
db''DRIVER''; char device name, 8 char, or
; If block device, no. Of units
; In first byte followed by
; 7 don''t care bytes
; Interpretation of Attribute word:
;
; Bit Significance
;
; 15 = 1 for character drivers
; 14 = 1 if driver can handle IOCTL
; 13 = 1 if block device & non-IBM format
; 12 0
; 11 open / close / RM supported (DOS 3.x)
; 100
; 90
; 80
; 70
; 60
; 50
; 40
; 3 = 1 if CLOCK device
; 2 = 1 if NUL device
; 1 = 1 if Standard Output
; 0 = 1 if Standard Input
page
;
; Local variables for use by driver
;
RH_Ptr dd?; Pointer to request header
; Passed to Strat by BDOS
Ident db cr, lf, lf
db''LMI Example Device Driver 1.0''
db cr, lf
db''Copyright (c) 1985''
db''Laboratory Microsystems Inc.''
db cr, lf, lf, eom
;
; MS-DOS Command Codes dispatch table.
; The "Interrupt" routine uses this table and the
; Command Code supplied in the Request Header to
; Transfer to the appropriate driver subroutine.
Dispatch:
dw Init; 0 = init driver into system
dw Media_Chk; 1 = media check on blk dev
dw Build_Bpb; 2 = build BIOS param block
dw Ioctl_Inp; 3 = I / O ctrl read from dev
dw Input; 4 = normal destructive read
dw Nd_Input; 5 = non-destructive read, no wait
dw Inp_Stat; 6 = return current input status
dw Inp_Flush; 7 = flush device input buffers
dw Output; 8 = normal output to device
dw Outp_Vfy; 9 = output with verify
dw Outp_Stat; 10 = return current output status
dw Outp_Flush; 11 = flush output buffers
dw Ioctl_Outp; 12 = I / O control output
dw Dev_Open; 13 = device open (MS-DOS 3.x)
dw Dev_Close; 14 = device close (MS-DOS 3.x)
dw Rem_Media; 15 = removeable media (MS-DOS 3.x)
page
;
; MS-DOS Request Header structure definition
;
; The first 13 bytes of all Request Headers are the same
; And are referred to as the "Static" part of the Header.
; The number and meaning of the following bytes varies.
; In this "Struc" definition we show the Request Header
; Contents for Read and Write calls.
;
Request struc; request header template structure
; Beginning of "Static" portion
Rlength db?; Length of request header
Unit db?; Unit number for this request
Command db?; Request header''s command code
Status dw?; Driver''s return status word
Reserve db 8 dup (?); Reserved area
; End of "Static" portion
Media db?; Media descriptor byte
Address dd?; Memory address for transfer
Count dw?; Byte / sector count value
Sector dw?; Starting sector value
Request ends; end of request header template
;
; Status word is interpreted as follows:
;
; Bit (s) Significance
; 15 Error
; 10-14 Reserved
; 9 Busy
; 8 Done
; 0-7 Error code if bit 15 = 1
; Predefined BDOS error codes are:
;
; 0 Write protect violation
; 1 Unknown unit
; 2 Drive not ready
; 3 Unknown command
; 4 CRC error
; 5 Bad drive request structure length
; 6 Seek error
; 7 Unknown media
; 8 Sector not found
; 9 Printer out of paper
; 10 Write fault
; 11 Read fault
; 12 General failure
; 13-14 Reserved
; 15 Invalid disk change (MS-DOS 3.x)
page
; Device Driver "Strategy Routine"
; Each time a request is made for this device, the BDOS
; First calls "Strategy routine", then immediately calls
; The "Interrupt routine".
; The Strategy routine is passed the address of the
; Request Header in ES: BX, which it saves in a local
; Variable and then returns to the BDOS.
Strat proc far
; Save address of Request Header
mov word ptr cs: [RH_Ptr], bx
mov word ptr cs: [RH_Ptr +2], es
ret; back to BDOS
Strat endp
page
; Device Driver "Interrupt Routine"
; This entry point is called by the BDOS immediately after
; The call to the "Strategy Routine", which saved the long
; Address of the Request Header in the local variable "RH_Ptr".
; The "Interrupt Routine" uses the Command Code passed in
; The Request Header to transfer to the appropriate device
; Handling routine. Each command code routine is responsible
; For any necessary return information into the Request Header,
; Then transfers to Error or Exit to set the Return Status code.
Intr proc far
push ax; save general registers
push bx
push cx
push dx
push ds
push es
push di
push si
push bp
push cs; make local data addressable
pop ds
les di, [RH_Ptr]; ES: DI = Request Header
; Get BX = Command Code
mov bl, es: [di.Command]
xor bh, bh
cmp bx, Max_Cmd; make sure its legal
jg Unk_Command; too big, exit with error code
shl bx, 1; form index to Dispatch table
; And branch to driver routine
jmp word ptr [bx + Dispatch]
page
; General collection of exit points for the driver routines.
Unk_Command:; Come here if Command Code too big.
mov al, 3; Sets "Unknown Command" error
; Code and "Done" bit.
Error:; Transfer here with AL = error code.
mov ah, 81h; Sets "Error" and "Done" bits.
jmp Exit
Done: mov ah, 1; Come here if I / O complete and
; No error, sets "Done" bit only.
Exit:; General purpose exit point.
; Transfer here with AX =
; Return Status word to be
; Placed into Request Header.
lds bx, cs: [RH_Ptr]; set status
mov ds: [bx.Status], ax
pop bp; restore general registers
pop si
pop di
pop es
pop ds
pop dx
pop cx
pop bx
pop ax
ret; back to BDOS
page
; Function 1 Media Check
; Block devices only. Should be a NOP for character devices.
;
; This routine is called first by BDOS for a block device transfer,
; Passing current media descriptor byte at Request Header +
;
; Media Check routine sets status word and in addition passes back
; Return byte at Request Header + 14 as follows:
; -1 Media has been changed
; 0 Don''t know if media changed
; 1 Media has not been changed
;
; If driver can return 1 or -1, performance is improved because
; MS-DOS does not need to reread the FAT for each directory access.
Media_Chk:
jmp Done
page
;
; Function 2 Build BIOS Parameter Block
;
; Block devices only. Should be a NOP for character devices.
;
; This routine is called by MS-DOS when Media-Changed code is
; Returned by Media Check routine, or if Not Sure code is returned
; And there are no dirty buffers.
;
; Build BPB call receives pointer to one-sector buffer in Address
; Field of Request Header (offset 14). If "Non-IBM-Format" bit
; In attribute word is zero, the buffer contains the first sector
; Of the FAT including the media identification byte and should not
; Be altered by the driver. If the "Non-IBM-Format" bit is set,
; The buffer mabe used as scratch space.;; The Build BPB routine sets status and returns a DWORD pointer to; the new Bios Parameter Block at Request Header + 18.; Build_Bpb: jmp Done page;; Function 3 I / O Control Read ;; Only called if IOCTL bit set in Device Header Attribute word.;; Called with:;; Request Header + 13 BYTE Media descriptor byte from DPB; Request Header + 14 DWORD Transfer address; Request Header + 18 WORD byte / sector count; Request Header + 20 WORD starting sector no. (block dev.);; Returns the Return Status word set appropriately, and; Request Header + 18 WORD actual bytes or sectors transferred;; No error check is performed on IOCTL I / O calls. Ioctl_Inp: jmp Done page;; Function 4 Read from Device;; Called with;; Request Header + 13 BYTE Media descriptor byte from DPB; Request Header + 14 DWORD Transfer address; Request Header + 18 WORD byte / sector count; Request Header + 20 WORD starting sector no. (block dev.);; Returns the Return Status word set appropriately, and; Request Header + 18 WORD actual bytes or sectors transferred Input: jmp Done page;; Function 5 Non-destructive Read from Device;; Character devices only.;; If Input Status request returns Busy bit = 0 (characters; waiting),; the next character that would be read is returned; at Request Header + 13. This character is not removed from; the Input Buffer. This basically provides the capability to; "look-ahead" by one character. Nd_Input: jmp Done page;; Function 6 Input Status;; Character devices only.;; Sets the Returned Status word:; Done bit = 1; Busy bit = 1 read request would go to physical device; = 0 characters already in device buffer, read request; would return quickly.;; MS-DOS assumes all character devices have type-ahead buffer.; If device does not have type-ahead buffer, should always; return Busy bit = 0 so MS-DOS will not hang. Inp_Stat: jmp Done page;; Function 7 Flush Input Buffers;; Character devices only.;; Terminate all pending requests, ie the Input buffer is; emptied. Inp_Flush : jmp Done page;; Function 8 Write to Device;; Called with;; Request Header + 13 BYTE Media descriptor byte from DPB; Request Header + 14 DWORD Transfer address; Request Header + 18 WORD byte / sector count; Request Header + 20 WORD starting sector no. (block dev.);; Returns the Return Status word set appropriately, and; Request Header + 18 WORD actual bytes or sectors transferred Output: jmp Done page;; Function 9 Write with Verify to Device;; Called with ;; Request Header + 13 BYTE Media descriptor byte from DPB; Request Header + 14 DWORD Transfer address; Request Header + 18 WORD byte / sector count; Request Header + 20 WORD starting sector no. (block dev.);; Returns the Return Status word set appropriately, and; Request Header + 18 WORD actual bytes or sectors transferred Outp_Vfy: jmp Done page;; Function 10 Output Status;; Character devices only.;; Sets the Returned Status word:; Done bit = 1; Busy bit = 1 write request would wait for completion of; current request; = 0 device idle, write request would start immediately.; Outp_Stat: jmp Done page;; Function 11 Flush Output Buffers;; Character devices only.;; Terminate pending requests. The output buffer, if any,; is emptied. Outp_Flush: jmp Done page;; Function 12 I / O Control Write;; Only called if IOCTL bit in Device Header Attribute word is set.;; Called with;; Request Header + 13 BYTE Media descriptor byte from DPB; Request Header + 14 DWORD Transfer address; Request Header + 18 WORD byte / sector count; Request Header + 20 WORD starting sector no. (block dev.);; Returns the Return Status word set appropriately, and; Request Header + 18 WORD actual bytes or sectors transferred;; No error check is performed on IOCTL calls. Ioctl_Outp: jmp Done page;; Function 13 Device Open;; MS-DOS version 3.0 and above only.; Only called if OPEN / CLOSE / RM bit set in Attribute word.; May be used to manage local buffering. Reference count; is incremented keeping track of number of open files on; the device. On character devices can be used to send; device initialization string, which can be set by IOCTL; Write. Note that CON AUX and PRN devices are always open.;; Returns the Return Status word set to "Done".; Dev_Open: jmp Done page;; Function 14 Device Close;; MS-DOS version 3.0 and above only.; Only called if OPEN / CLOSE / RM bit set in Attribute word.; May be used to manage local buffering. Reference count; is decremented keeping track of number of open files on; the device; when count reaches zero all files have been closed; and the driver should flush buffers as user may change disks.; On character devices can be used to send device post-I / O; string such as a form feed, which can be set by IOCTL; Write. Note that CON AUX and PRN devices are never closed.;; Returns the Return Status word set to "Done".; Dev_Close: jmp Done page;; Function 15 Removeable Media;; MS-DOS version 3.0 and above only.; Only called if OPEN / CLOSE / RM bit set in Attribute word; and device type is block.;; Returns the Return Status word set to "Done" and; Busy bit = 1 if media is non-removable.; = 0 if media is removable. ; Rem_Media: jmp Done page ; This Initialization code for the driver is called only ; once when the driver is loaded. It is responsible for ; initializing the hardware, setting up any necessary ; interrupt vectors, and it must return the address ; of the first free memory after the driver to the BDOS. ; If it is a block device driver, Init must also return the ; address of the Bios Parameter Block pointer array; if all ; units are the same, all pointers can point to the same BPB. ; Only MS-DOS services 01-0CH and 30H can be called by the ; Initialization function. ; ; In this example, Init returns its own address to the DOS as ; the start of free memory after the driver, so that the memory ; occupied by IN99v will be reclaimed after it is finished ; with its work. ; ; Called with: ; ; Request Header + 18 DWORD pointer to the character after the "=" ; on the CONFIG.SYS line that loaded ; driver; this information is read only. ; 22 BYTE drive letter for first unit of a ; block driver (0=A 1=B etc) ; (MS-DOS 3.x only) ; ; Returns: ; ; Request Header + 13 BYTE Number of units (block devices only) ; + 14 DWORD address of first free memory above driver ; + 18 DWORD BPB pointer array (block devices only) ; Init: ; Function 0 ; initialize device driver push es ; push Request Header addr push di mov ah,9 ; print sign-on message mov dx,offset Ident int 21h pop di ; restore Request Header addr pop es ; set first usable memory addr. mov word ptr es:[di.Address],offset Init mov word ptr es:[di.Address+2],cs jmp Done Intr endp Driver endp code ends end
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