Category : Files from Magazines
Archive   : WDJAN92.ZIP
Filename : 3N01052A

;-----------------------------------------------------------------------;
; INITVID.ASM, Written Sept 1991 by Jonathan Wood, SoftCircuits ;
; ;
; Routines to determine host display adapter. Assembled using MASM 6.0. ;
; To assemble for different C memory models, modify the .MODEL ;
; directive to the correct model and recompile. To interface with other ;
; languages, change the language specifier on the same line. Depending ;
; on the language, you may need to modify the way parameters are ;
; accessed and which registers are saved. ;
;-----------------------------------------------------------------------;

.MODEL small,c ;Specify memory model/language

MONO_SEG EQU 0B000h ;Standard display segments
COLOR_SEG EQU 0B800h

.DATA
video_segment DW COLOR_SEG ;Display memory segment address
video_type DB 0FFh ;Display combination code
video_iscolor DB 01h ;1 = color, 0 = mono
video_mode DB 03h ;Video display mode
video_page DB 00h ;Video display page
video_rows DB 25h ;Number of text rows
video_cols DB 80h ;Number of text columns

.CODE
;-----------------------------------------------------------------------;
; Determines the active display adapter and various display parameters. ;
; ;
; Prototype: void initvideo(void); ;
; ;
;-----------------------------------------------------------------------;
initvideo PROC USES si di bp
mov ah,0Fh ;Read video information
int 10h
mov video_mode,al ;Video display mode
mov video_page,bh ;Video display page
mov video_cols,ah ;Number of text columns
mov video_segment,MONO_SEG ;Assume mono display for now
mov video_iscolor,0
int 11h ;Read equipment list
and al,00110000b ;Isolate video bits
cmp al,00110000b ;Was it mono?
je find_adapter ;Yes
mov video_segment,COLOR_SEG ;Else set color display
mov video_iscolor,1
find_adapter:
call ps2_state ;Read PS/2 video state
jnz adapter_set ;Done if supported
call ega_state ;Read EGA video state
jnz adapter_Set ;Done if supported
call cga_state ;Determine CGA or MDA
adapter_set:
sub ax,ax ;Adjust display segment for
mov es,ax ; current video page
mov ax,es:[044Eh]
mov cl,4
shr ax,cl
add video_segment,ax
ret
initvideo ENDP

;-----------------------------------------------------------------------;
; This procedure attempts to access PS/2 compatible ROM BIOS video ;
; services. The zero flag is set if they aren't supported. ;
; ;
; Output: zf Zero flag set if PS/2 compatible ROM BIOS is ;
; not present. ;
; ;
;-----------------------------------------------------------------------;
ps2_state PROC NEAR
mov ax,1A00h ;Read PS/2 display code
int 10h
cmp al,1Ah ;Was function supported?
lahf ;Toggle zero flag (zf = 1 if
xor ah,01000000b ; al is not equal to 1Ah)
sahf
jz no_ps2 ;PS/2 BIOS not present
mov video_type,bl ;Save active display code
mov ax,1130h ;Read font code
sub bh,bh ;Font code (not used)
int 10h
inc dl ;Adjust row count (clears zf)
mov video_rows,dl ; and save
no_ps2:
ret
ps2_state ENDP

;-----------------------------------------------------------------------;
; If PS/2 compatible ROM BIOS is not present, this procedure attempts ;
; to access the EGA ROM BIOS video services. ;
; ;
; Output: zf Zero flag set if EGA not active ;
; ;
;-----------------------------------------------------------------------;
ega_state PROC NEAR
mov ah,12h ;Read EGA video state
mov bl,10h
int 10h
cmp bl,10h ;Was function supported?
je no_ega ;No, EGA BIOS not present
cmp video_iscolor,bh ;Is EGA the active display
je no_ega ;No, find active display
add bh,4 ;Else calculate display code
mov video_type,bh ; and save
mov ax,1130h ;Read font code
sub bh,bh ;Font code (not used)
int 10h
inc dl ;Adjust row count (clears zf)
mov video_rows,dl ; and save
no_ega:
ret
ega_state ENDP

;-----------------------------------------------------------------------;
; This procedure is called if neither PS/2 or EGA comaptible ROM BIOS ;
; was active. It simply assumes 25 text rows and sets video_type to MDA ;
; or CGA depending on the value of video_iscolor. ;
;-----------------------------------------------------------------------;
cga_state PROC NEAR
mov video_rows,25 ;If we get here, must be 25 rows
mov video_type,01h ;Assume MDA display adapter for now
cmp video_iscolor,0 ;Is it mono?
je no_cga ;Yes
mov video_type,02h ;Else set CGA display adapter
no_cga:
ret
cga_state ENDP

;-----------------------------------------------------------------------;
; This routine fills a buffer with the current video parameter values. ;
; Note: initvideo() must be called first in order for this procedure to ;
; return meaningful values. ;
; ;
; Usage: void getvconfig(struct video *); ;
; ;
; Where: struct video { ;
; int segment; ;
; int type; ;
; int iscolor; ;
; int mode; ;
; int page; ;
; int rows; ;
; int columns; ;
; }; ;
; ;
;-----------------------------------------------------------------------;
getvconfig PROC USES si di, buffer:PTR
cld
IF @DataSize
les di,buffer ;Load far struct pointer into es:di
ELSE
mov di,buffer ;Load near struct pointer into es:di
push ds
pop es
ENDIF
mov si,OFFSET video_segment ;ds:si points to display variables
lodsw ;Copy video segment to buffer
stosw
mov cx,6 ;Copy 6 more byte values
sub ah,ah ;Clear high byte of ax
copy_loop:
lodsb ;Load byte value in al
stosw ;Copy word value to buffer
loop copy_loop
ret
getvconfig ENDP

END