boot1.asm

Jazmyn is a 32-bit, protected mode, multitasking OS which runs on i386 & above CPU`s. Its complete

;Copyright 2004, Thejesh AP ,ALL rights reserved.

;______________________________________________________________________________________________;
;											      			     ;
; FAT-32 boot sector as per Microsoft specification.   					           ;
;______________________________________________________________________________________________;
 

code_seg segment use16
assume cs:code_seg

jmp start

BS_OEMName              db      'JAZMYN.1'      ;Not required by Microsoft Os`s,but some FAT drivers need this
BPB_BytesPerSec	dw	512		;bytes/sector = 512
BPB_SecPerClus	db	8		;sect/clust = 4;1clust = 2k
BPB_RsvSecCnt	dw	32		;# reserved sect in reserved region
BPB_NumFats		db	1		;# FAT copies is 2
BPB_RootEntCnt	dw	0		;for FAT12/16,this contains count of 32byte root dir entries
BPB_TotSec16	dw	0		;old 16-bit total cnt of sectors.Not used in FAT32
BPB_Media		db	0F8h		;Media type : fixed non removable media
BPB_FATSz16		dw	0		;# sectors occupied by FAT12/16
BPB_SecPerTrk	dw	63		;sectors/track = 63 for int 0x13
BPB_NumHeads	dw	16		;heads/cylindr=16/128 for int 0x13
BPB_HiddSec		dd	?		;# hidden secs preceding partition
BPB_TotSec32	dd	20097		;32bit cnt of # sectors
BPB_FATSz32		dd	20		;# sectors occupied by one FAT
BPB_ExtFlags	dw	0		;flags
BPB_FSVer		dw	0		;fs version 0:0
BPB_RootClus	dd	2		;cluster no of the first cluster of root dir
BPB_FSInfo		dw	1		;sect no of FSINFO struct in reserved area
BPB_BkBootSec	dw	6		;sect no of copy of boot record
BPB_Reserved	db	12 dup(0)	;reserved by Microsoft for future expansion
BS_DrvNum		db	80h		;BIOS drive number 0x80 for HD
BS_Reserved1	db	0		;reserved,used by Windows NT
BS_BootSig		db	29h		;extended boot signature
BS_VolID		dd	?		;vol id - generated by combining curr date & time
BS_VolLab		db	11 dup(0)	;volume label set by format prog
BS_FileSysType	db	'FAT32   '	;fs type

Jaz_No386M		db	'Sorry. Jazmyn needs atleast 386',13,10,'Press a key to reboot',0
Jaz_Loading		db	'Loading Jazmyn....',0
Boot_Part		db	4

display proc near				;procedure : displays strings
prnt:	
	lodsb					;loads ds:si to al 
	or	al,al 
	jz	over
	mov	ah,0Eh			;function  
	mov	bh,0				;page no 0
	int	10h  
	jmp	prnt
over:
		ret
display endp


check_cpu proc near			;procedure : checks for 386 CPU if 386 then al=1 else al=0
	pushf					;save flags
	xor	ah,ah				;check for 86
	push	ax
	popf
	pushf
	pop	ax
	and	ah,0f0h
	cmp	ah,0f0h			;86 sets high nibble of flag register to 0xF
	je	no386
	mov	ah,0f0h			;check for 286
	push	ax
	popf
	pushf
	pop	ax
	and	ah,0f0h			;286 sets high nibble of flag register to 0
	jz	no386
	popf
	mov	al,1
	jmp	over
no386:
	popf
	mov	al,0
over:
	ret
check_cpu endp


key macro
	mov	ah,0
	int	16h
endm

start:
        mov     ax,07C0h
	mov	ds,ax

	cli					;setup boot stack
	mov	ax,1000h
	mov	ss,ax
	mov	sp,0ffffh
	sti
	
	mov	si,offset Jaz_Loading	;display start message
	call	display
	call	check_cpu			;check for a 386

	.if al == 0
		mov	si,offset Jaz_No386M
		key
		jmp	reboot
	.endif

	db	0eah
	dw	0000h
	dw	0100h
reboot:
	db	0eah
	dw	0000h
	dw	0ffffh

	org	510
	dw	0aa55h
        dd      41615252h
        org     1024
      
code_seg ends
end