From:	tmurez AT planete DOT net
Newsgroups:	alt.lang.asm,comp.lang.asm.x86,comp.os.msdos.djgpp
Subject:	Problem building a vesa lib with nasm&djgpp
Date:	13 Jul 1998 17:51:38 GMT
Organization:	Planete.net, France
Lines:	159
Approved:	<johnfine AT erols DOT com>
Message-ID:	<6odhfa$ec6$1@winter.news.erols.com>
NNTP-Posting-Host:	207-172-240-250.s59.as4.bsd.erols.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi,
(excuse my mistakes i m french)
I'm used to build programs with BC++ and his inline assembly. I wanted to 
use DMPI so i got DJGPP and NASM. I've written the following routine. My 
problems and what i noticed with fsdb (djgpp debugger) are written in the 
routine.
*************************************************************************
vbelib.asm :

[BITS 32]

[GLOBAL _VBE2Detect]

[SECTION .text]

;Function VBE2Detect();
;out : 0 if error or vesa 2 not available, 1 if vesa 2 or greater 
;							available

_VBE2Detect:
        pushad
        mov AX, 0100h ;DPMI Allocate DOS Memory Block int 31h fct 100h
        mov BX, 32    ;32 paragraphs equ to 512 bytes (vesa info header)
        int 31h
        jnc .MemoireAllouee		;jump if memory allocated
        popad				;else pop registers and return 0
        xor eax, eax
        ret

        .MemoireAllouee:
                mov [DOSMEM_RMSEG], AX  ;save real mode segment
                mov [DOSMEM_SELECTOR], DX ;save mem selector
                mov ecx, eax	;ecx will be linear address
                and ecx, 0FFFFh	;clear high 16bits
                shl ecx, 4		;seg*16
                mov [DOSMEM_LINADDR], ECX ;save linear address

                mov dword [ecx+VbeInfoBlock+VbeSignature], 'VBE2'
				;asking for VBE 2.0 Info
                push ds
                pop es          ;es=ds to prevent GPF
                mov EDI, RMREGS ;edi=offset RMREGS
                mov dword [RM_EAX], 04F00h ;VESA Fct 00h
                mov dword [RM_EDI], 0	;offset dosmem=0
                mov word [RM_ES], AX	;segment returned from int31h
                mov AX, 0300h           ;DPMI Simulate Real ModeInterrupt
                mov BX, 0010h		;real mode int 10h
                xor CX, CX			;cx=0
                int 31h
                jnc .Interrupt31Succes ;jump if success
		;else free dos mem and return 0
                mov AX, 0101h   ;DPMI Free DOS Memory Block
                mov DX, [DOSMEM_SELECTOR]
                int 31h
                popad
                xor EAX, EAX
                ret

        .Interrupt31Succes:
                mov eax, [RM_EAX]
                cmp dword AX, 04Fh		;Check if Vesa fct call succeed
                je .InterruptVbeSucces	;jump if success
			;else free dos mem and return 0
                mov AX, 0101h
                mov DX, [DOSMEM_SELECTOR]
                int 31h
                popad
                xor eax, eax
                ret


	;using fsdb i can tell everything works fine until here.
	;the dosmem is still not used by vesa and the follwing comp
	; fails because dosmem[0]=VBE2 !
	;I tried to use a dumb seg and offs with vesa function and it
	;returned 4fh(success) so i think the pb is that im not using
	;the good real mode address...
	;i think i need an advise on using dpmi fct 100h

        .InterruptVbeSucces:
                mov ecx, [DOSMEM_LINADDR]
                cmp dword [ecx+VbeInfoBlock+VbeSignature], 'ASEV'
                je .VESADetecte

                mov AX, 0101h
                mov DX, [DOSMEM_SELECTOR]
                int 31h
                popad
                xor eax, eax
                ret

        .VESADetecte:
                cmp word[ecx+VbeInfoBlock+VbeVersion], 0200h
                jge .VBE2

                mov AX, 0101h
                mov DX, [DOSMEM_SELECTOR]
                int 31h
                popad
                xor eax, eax
                ret

        .VBE2:
                mov AX, 0101h
                mov DX, [DOSMEM_SELECTOR]
                int 31h
                popad
                xor eax, eax
                inc eax
                ret


[SECTION .data]

        DOSMEM_RMSEG            dw      0      
        DOSMEM_SELECTOR         dw      0      
        DOSMEM_LINADDR          dd      0      

        struc VbeInfoBlock
                VbeSignature        resb 4     ; VBE Signature
                VbeVersion          resw 1     ; VBE Version
                OemStringPtr        resd 1     ; Pointer to OEM String
                Capabilities        resb 4;Capabilities of graphics cont.
                VideoModePtr        resd 1   ; Pointer to Video Mode List
                TotalMemory         resw 1 ; Number of 64kb memory blocks
        	     ; Added for VBE 2.0
                OemSoftwareRev      resw 1 ; VBE implementation Software 
revision
                OemVendorNamePtr    resd 1         ; Pointer to Vendor 
Name String
                OemProductNamePtr   resd 1         ; Pointer to Product 
Name String
                OemProductRevPtr    resd 1         ; Pointer to Product 
Revision String
                Reserved            resb 222       ; Reserved for VBE 
implementation
						    ; scratch area
                OemData             resb 256       ; Data Area for OEM 
Strings
        endstruc

        RMREGS:
                RM_EDI          dd      0
                RM_ESI          dd      0
                RM_EBP          dd      0
                RM_Reserved     dd      0
                RM_EBX          dd      0
                RM_EDX          dd      0
                RM_ECX          dd      0
                RM_EAX          dd      0
                RM_Flags        dw      0
                RM_ES           dw      0
                RM_DS           dw      0
                RM_FS           dw      0
                RM_GS           dw      0
                RM_IP           dw      0
                RM_CS           dw      0
                RM_SP           dw      0
                RM_SS           dw      0

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