[syslinux] isolinux.asm - improving spec_query_failed routine...

[Lagerweij B]

Hi Peter,

I noticed in your isolinux.asm code,
when loading spec packet fails you are trying to wing it, in other word,
loop the drive numbers from 0xff through 0x80 until the booted drive number
is found...

I write software that also "wings it".
Recently I had to create some "wird" workarounds because of bad bios in some
Dell and Compaq PC's.

Below is my function for finding (wing it) the booted eltorito drive number,
this methode works on the worst and badly coded bioses out there...
Maybe it can help you with development of future version of isolinux.asm

You provide isolinux for the world, for free, so improving your code is the
least I can do back...

Best regards and good luck,
Bart "nu2" Lagerweij.

---
Bart Lagerweij - http://www.nu2.nu
To contact me go here: http://www.nu2.nu/contact/bart
---


;------------------------------------------------------------
; Get first emulated drive number
; returns:
;	CF=1 - not in emulation mode
;	CF=0 - in emulation mode
;	DL - drive number for emulation
get_emul_drive:
	push	ax
	push	si

;	mov	[spec_packet], 13h
	mov	dl, 0ffh		; drive number
get_emul_drive1:
	mov	ax, 4b01h		; get status
	mov	[spec_packet], 0
	call	int13
; Bogus Dell PC's do not return carry flag correctly - ignoring it
;	jnc	get_emul_drive_ok


; some bogus bioses (Dell Inspiron 2500) returns packet size 0xff when
failed
; Dell Dimension XPsT returns packet size 0x14 when OK
	cmp	[spec_packet], 13h	; anything between 13h and 20h
should be OK
	jb	get_emul_trynext
	cmp	[spec_packet], 20h
	ja	get_emul_trynext
	jmp	short get_emul_drive_ok
	
get_emul_trynext:
	dec	dl
	cmp	dl, 80h
	jb	get_emul_drive_nok
	jmp	get_emul_drive1

;	cmp	[spec_packet], 0
;	je	get_emul_trynext
;	jmp	get_emul_drive_ok

get_emul_drive_nok:
	xor	dl, dl
	stc
	jmp	short get_emul_drive_exit

get_emul_drive_ok:
	mov	dl, [spec_packet+2]
	clc

get_emul_drive_exit:
	pop	si
	pop	ax
	ret

;------------------------------------------------------------

int13:
	mov	si, offset spec_packet
	int	13h
	
	ret
;------------------------------------------------------------