Assembly
Shows one possible method for checking the type of video card
Shows one possible method for checking the type of video card installed in a system comment ^ Sample code to show how one might detect video cards by using search strings. ^ .model small .stack 400h .data ;/*************************************************************************** ; some handy equates ;***************************************************************************/ VID_BIOS_SEG equ 0c000h ; the video BIOS segment SEARCH_AREA equ 0400h ; when we look for the video BIOS ; ID, we only seach this many bytes CMP_LENGTH equ 7 ; the number of "significant" ; characters to compare in each ; string DOS_INT equ 21h ; DOS' interrupt VIDEO_INT equ 10h ; BIOS' video services int VID_80x25 equ 03h ; 80x25 text mode number ;/*************************************************************************** ; data ;***************************************************************************/ UnknownCardMsg db 'Your video card is not supported.',13,10,'$' mode1 db 053h ; 640 x 480 x 256 mode for Oak card1 db 'OAK VGA','$' mode2 db 05dh ; 640 x 480 x 256 mode for Trident card2 db 'TRIDENT','$' cards dw card1, card2, 0 ;/*************************************************************************** ; some handy macros ;***************************************************************************/ @DosPrint MACRO msgptr mov dx,msgptr ; handy macro for printing mov ah,9 ; '$' terminated strings int DOS_INT ; under DOS ENDM @SetVidMode MACRO vmode ifnb <vmode> mov ax,(vmode AND 0ffh) else xor ah,ah endif int VIDEO_INT ENDM .code ;/*************************************************************************** ; main ; This is the main procedure in the code. It identifies (or ; attempts to identify) the type of video card, then switches into ; the appropriate video mode for that type of card. Right now, it ; doesn't actually do anything in that mode, but simply returns ; and restores the video mode to a fairly standard 80x25 text ; mode. Mostly as an aid to troubleshooting, the current version ; also prints out the name of the video card as discovered in the ; video BIOS area. ; ;***************************************************************************/ main proc .STARTUP ; do the usual startup stuff call IDVideoBios ; identify video BIOS or si,si ; Q: unknown card? jz NoSupport ; Y: tell the user the bad news dec si ; point to video mode (mode1, mode2) lodsb ; load into al & increment si @SetVidMode ; change video mode ; ; snazzy graphics code goes here ; @SetVidMode <VID_80x25> ; switch back to 80x25 text mode @DosPrint <si> ; print ID string .EXIT 0 ; exit with error code = 0 NoSupport: @DosPrint <offset UnknownCardMsg> ; print unknown card message .EXIT 1 ; exit with error code = 1 main endp ;/*************************************************************************** ; IDVideoBios ; ; This procedure searches the first SEARCH_AREA bytes in the video ; BIOS for a byte sequence which uniquely identifies a video ; card's manufacturer. If no known card name is found, the ; function returns a null pointer. ; ; Entry: DS contains the segment of the cards array ; ; Exit: If a match was found, ; DS:SI ==> matching sequence ; otherwise ; SI = 0 ; ; Destroyed: none ; ;***************************************************************************/ IDVideoBios proc push ax ; save used regs push bx ; push cx ; push es ; mov ax,VID_BIOS_SEG ; point to video BIOS mov es,ax ; mov bx,OFFSET cards ; point to first card entry cld ; we'll be scanning forward next_card: mov si,[bx] ; or si,si ; Q: is it a NULL pointer? jz @@exit ; Y: we're done, so exit now xor di,di ; es:di ==> video BIOS area mov cx,SEARCH_AREA ; mov al,[si] ; get the first letter scan: repne scasb ; scan for AL in es:di jnz nofind ; if we didn't find it, skip over ; ; if we got here, ES:DI points to one letter after the matching letter ; in the video BIOS. We need to compare the rest to assure that we have ; a complete match. ; push cx ; temporarily save regs push di ; push si ; inc si ; point to next letter mov cx,CMP_LENGTH-1 ; compare the rest the string repe cmpsb ; do it pop si ; restore regs pop di ; pop cx ; jz @@exit ; if match, we're done nofind: or cx,cx ; Q: is the count down to zero? jnz scan ; N: keep scanning inc bx ; Y: point to next card inc bx ; point to next card entry jmp next_card ; go back for more @@exit: pop es ; restore used registers pop cx ; pop bx ; pop ax ; ret ; IDVideoBios endp end
Shows one possible method for checking the type of video card
