Category : Files from Magazines
Archive   : MAY91.ZIP
Filename : 2N05026A

title Net_CD
page 59, 132
;
; File: Net_CD.ASM
; Purpose: Workstation client device driver for
; remote CDROM access
; Description: This file contains the device driver
; header and the standard strategy and
; interrupt routines, as well as some
; of the initialization code and
; interfaces to BIOS, DOS, and NetBIOS
; functions.
;

subttl Structure definitions
page +
;
; Standard device driver header
;
rh struc

rh_length db ? ; header size, bytes
rh_unit db ? ; block dev. unit #
rh_command db ? ; device command code
rh_status dw ? ; device command status
rh_reserved db 8 dup (?)
rh ends

;
; INIT command header extensions
;
rh0 struc

rh0_rh db size rh dup (?)
rh0_numUnits db ? ; number block units
rh0_brkAddress dd ? ; end of driver address
rh0_bpb dd ? ; BIOS parameter block
rh0_devNumber db ? ; block device number
rh0 ends

subttl 'C' Driver Functions
page +
;
; Externally linked 'C' function declarations
;
extrn _UnknownCommand:near
extrn _Initialize:near
extrn _DevOpen:near
extrn _DevClose:near
extrn _IOInput:near
extrn _IOOutput:near

extrn _ReadLong:near
extrn _ReadPrefetch:near
extrn _Seek:near


subttl Segment Declarations
page +
;
; Segments are declared with _DATA first to allow the
; device driver header to appear at offset 0 within the
; driver at load time. _BSS and CONST are present to
; handle normal MS-C code emissions. _TEXT and INIT are
; declared last to allow for easy discarding of the
; driver Initialize routine.
;
DGROUP group _DATA, _BSS, CONST, _TEXT, INIT

_DATA segment word PUBLIC 'DATA'
assume ds:DGROUP
_DATA ends

_BSS segment word PUBLIC 'BSS'
assume ds:DGROUP
_BSS ends

CONST segment word PUBLIC 'CONST'
assume ds:DGROUP
CONST ends

_TEXT segment word PUBLIC 'CODE'
assume cs:DGROUP, ds:DGROUP
_TEXT ends

INIT segment word PUBLIC 'INIT'
assume cs:DGROUP, ds:DGROUP
INIT ends

subttl Net_CD Data Segment
page +

_DATA segment

Net_CD:

;
; Public declarations for initialization code
;
PUBLIC _DevHeader
;
; Device driver header with CDROM extension fields
;
_DevHeader label word
dd -1 ; next driver
dw 0c800h ; device attributes
dw DGROUP:DevStrategy
dw DGROUP:DevInterrupt
db 'NET-CD '
dw 0 ; CDROM reserved
db 0 ; CDROM drive letter
db 1 ; number of units

;
; Local data for function dispatcher
;
rh_offset dw ? ; Req Hdr pointer
rh_segment dw ?

save_sp dw ? ; old stack save
save_ss dw ? ; area

local_stack dw 256 dup ('s') ; local stack
top_stack dw DGROUP:$ ; me and 'C'

;
; Driver standard commands jump table
;
DevCmdTbl label word
dw DGROUP:_Initialize
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_IOInput
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_IOOutput
dw DGROUP:_DevOpen
dw DGROUP:_DevClose
dw DGROUP:_UnknownCommand

;
; CDROM extended commands jump table
;
DevExtCmdTbl label word
dw DGROUP:_ReadLong
dw DGROUP:_UnknownCommand
dw DGROUP:_ReadPrefetch
dw DGROUP:_Seek
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand
dw DGROUP:_UnknownCommand


_DATA ends

subttl Net_CD Text Segment
page +

;
; Assembly language portion of the Text segment contains
; the standard driver Strategy and Interrupt routines as
; well an interface routine to NetBIOS
;

_TEXT segment

;
; Device Strategy routine
; Save request header pointer for subsequent call to
; Interrupt routine.
;

DevStrategy proc far

mov cs:rh_offset, bx
mov cs:rh_segment, es
ret

DevStrategy endp

;
; Device Interrupt routine
; DevInterrupt sets up a stack for the 'C' routines
; and validates the command before dispatching it to
; an appropriate handler.
;

DevInterrupt proc far

; save calling context
pushf
push ax
push bx
push cx
push dx
push si
push di
push ds
push es

; setup addressing for local and 'C'
mov ax, cs
mov ds, ax

; switch to local stack
mov save_sp, sp
mov save_ss, ss
mov ss, ax
mov sp, top_stack

; reload request header pointer
mov ax, rh_segment
mov es, ax
mov bx, rh_offset

; prepare for call to handlers
push es
push bx

; process command
mov al, es:[bx].rh_command
xor ah, ah
cmp al, 128 ; CDROM cmd?
jae IntCDROMCmd

cmp al, 15 ; valid cmd?
jb IntStdCmd

IntInvalid: mov ax, 8013h ; set unknown
jmp IntExit

IntCDROMCmd: sub al, 128
cmp al, 8 ; valid CDROM?
ja IntInvalid

shl ax, 1 ; dispatch to
mov si, ax ; handler
call DevExtCmdTbl[si]
jmp IntExit

IntStdCmd: shl ax, 1 ; dispatch to
mov si, ax ; handler
call DevCmdTbl[si]

; set up exit status
IntExit: pop bx
pop es
mov es:[bx].rh_status, ax

; reset calling context
mov ss, save_ss
mov sp, save_sp

pop es
pop ds
pop di
pop si
pop dx
pop cx
pop bx
pop ax
popf

ret
even
DevInterrupt endp

;
; _NetBIOS : void NetBIOS (NCB far *)
; Call NetBIOS at INT 5C. This function assumes
; NetBIOS has been loaded and makes no checks to
; verify that.
;

PUBLIC _NetBIOS
_NetBIOS proc near
push bp
mov bp, sp

; set es:bx to point to NCB and go
push bx
push es
mov bx, [bp+4]
mov ax, [bp+6]
mov es, ax
int 5ch

pop bx
pop es
pop bp
ret
_NetBIOS endp


_TEXT ends

subttl Net_CD INIT Segment
page +

;
; Driver INIT segment
; Having the Initialize function linked last guarantees
; that it appears last in the _TEXT segment. Since this
; segment comes after the _TEXT segment when Initializes
; tells DOS to discard the data from _Initialize on all
; of this segment will disappear also.
;

INIT segment

;
; _DisplayString : void DisplayString (char *)
; Displays a string using DOS function 9. This function
; may only be used during device driver initialization.
;

PUBLIC _DisplayString
_DisplayString proc near

push bp
mov bp, sp

push di
push si

mov ah, 9 ; display str$
mov dx, [bp+4] ; string ptr.
int 21h

pop si
pop di
pop bp
ret
_DisplayString endp

;
; _SetEndAddress : void SetEndAddress (struc rh0 far *)
; Set the ending address of the device driver in the
; Initialize request header. The location of
; _Initialize is taken to be the location at which
; discardable data begins, which will effectively
; eliminate the INIT segment also.
;

PUBLIC _SetEndAddress
_SetEndAddress proc near

push bp
mov bp, sp

; get request header in es:di
push di
mov di, [bp+4]
mov ax, [bp+6]
mov es, ax

; set address in rh0_brkAddress
mov word ptr es:[di].rh0_brkAddress, offset DGROUP:_Initialize
mov word ptr es:[di].rh0_brkAddress+2, cs

pop di
pop bp
ret
_SetEndAddress endp


;
; Discardable initialization data
;
PUBLIC _banner, __acrtused
;
; Device Driver loading banner
;
_banner db 0dh, 0ah
db 'Net_CD.SYS: Workstation Client'
db ' Software Loaded'
db 0dh, 0ah, '$', 0

;
; So MSC doesn't complain - set a CRT being used
;
__acrtused dw 1

INIT ends


end Net_CD