; DRIVESEX.ASM - Drive existence detection      July 6th, 1994

; Code by       : Lee Hamel (hamell@cs.pdx.edu)

; Partial credit: Paul Schlyter

;

; Goes through drives A-Z and determines if they:

; 1) Exist

; 2) Are removable or fixed

; 3) Are local, remote, or shared

; 4) Are a floppy, hard, RAM, subst, or CD-ROM drive

;

; Callable from C as: void Drives_Exist(void);



.model small

.286



DRIVEEXIST      EQU     1



REMOVEDRV       EQU     0

FIXEDDRV        EQU     1



LOCALDRV        EQU     0

REMOTEDRV       EQU     1

SHAREDRV        EQU     2



FLOPPY          EQU     0

HARD            EQU     1

RAM             EQU     2

SUBST           EQU     3

CDROM           EQU     4



.data

PUBLIC  _drives

        _drives         db      26 dup(0,1,0,1)

        ; default to not exist, fixed, local, hard drive



.code



                        PUBLIC  _Drives_Exist

_Drives_Exist           PROC    NEAR

                pusha

                push    es



                mov     ah,19h

                int     21h             ; get start drive

                push    ax              ; save start drive



                mov     ax,40h

                mov     es,ax

                mov     bh,es:[10h]     ; 40:10h is # of floppies-1

                shr     bh,6

                inc     bh              ; # of actual floppy drives

                mov     bl,1

                mov     di,offset _drives

nextchkfloppy:  mov     ax,4409h        ; check if drive exists

                int     21h

                jc      nextsetfloppy

                test    dh,10000000b    ; check if SUBST drive

                jz      chkfloppy

                dec     bh              ; dec actual drive count

                mov     byte ptr [di 3],SUBST

setfloppyexist: mov     byte ptr [di],DRIVEEXIST

                jmp     nextsetfloppy

chkfloppy:      dec     bh              ; dec actual drive count

                js      nextsetfloppy

                mov     byte ptr [di 1],REMOVEDRV

                mov     byte ptr [di 3],FLOPPY

                jmp     setfloppyexist

nextsetfloppy:  add     di,4

                inc     bl

                cmp     bl,2            ; if B then jump back

                je      nextchkfloppy



                mov     ch,24           ; loop 24 times (drives C - Z)

                mov     cl,3            ; start at C:

drivechkloop:   mov     ax,4409h        ; check if drive exists

                mov     bl,cl           ; set drive letter

                int     21h             ; 0 = default, 1 = A:, etc.

                jc      nextsetdrv

                mov     byte ptr [di],DRIVEEXIST

                mov     ax,4408h        ; check if removable

                int     21h

                mov     byte ptr [di 1],al      ; set REMOVABLE or FIXED

                mov     bx,dx

                mov     dl,dh

                shr     dl,7

                and     dh,00010000b

                shr     dh,4

                mov     byte ptr [di 2],dh      ; set REMOTE or LOCAL

                or      dl,dl                   ; if not SUBST, then jump

                jz      chkremote

                mov     byte ptr [di 3],SUBST

                jmp     nextsetdrv



chkremote:      cmp     dh,REMOTEDRV    ; if REMOTE, then check for CD ROM

                je      chkcdrom



                test    bh,00000010b    ; sharable?

                jz      drivenoshare

                mov     byte ptr [di 2],SHAREDRV

drivenoshare:   test    bl,00000010b    ; RAM drive?

                jnz     nextsetdrv

                mov     byte ptr [di 3],RAM

                jmp     nextsetdrv



chkcdrom:       push    cx

                mov     ax,1500h

                xor     bx,bx

                int     2fh

                pop     cx

                or      bx,bx           ; MSCDEX driver found?

                jz      nextsetdrv      ; if not, jump to next drive setup

                mov     ax,150bh

                dec     cl              ; 0=A:, etc.

                int     2fh

                inc     cl

                or      ax,ax

                jz      nextsetdrv      ; drive supported by MSCDEX?

                mov     byte ptr [di 3],CDROM



nextsetdrv:     add     di,4

                inc     cl

                dec     ch

                jnz     drivechkloop



                pop     dx

                mov     ah,0eh

                int     21h             ; reset start drive



                pop     es

                popa

                ret

_Drives_Exist           ENDP



                        END