OSDev.org

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;*********************************************
;	Boot1.asm
;		- A Simple Bootloader
;
;	Operating Systems Development Tutorial
;*********************************************

bits	16							; We are still in 16 bit Real Mode

org		0x7c00						; We are loaded by BIOS at 0x7C00

start:          jmp loader					; jump over OEM block

;*************************************************;
;	OEM Parameter block / BIOS Parameter Block
;*************************************************;

TIMES 0Bh-$+start DB 0

bpbBytesPerSector:  	DW 512
bpbSectorsPerCluster: 	DB 1
bpbReservedSectors: 	DW 1
bpbNumberOfFATs: 	DB 2
bpbRootEntries: 	DW 224
bpbTotalSectors: 	DW 2880
bpbMedia: 	        DB 0xF0
bpbSectorsPerFAT: 	DW 9
bpbSectorsPerTrack: 	DW 18
bpbHeadsPerCylinder: 	DW 2
bpbHiddenSectors:       DD 0
bpbTotalSectorsBig:     DD 0
bsDriveNumber: 	        DB 0
bsUnused: 	        DB 0
bsExtBootSignature: 	DB 0x29
bsSerialNumber:	        DD 0xa0a1a2a3
bsVolumeLabel: 	        DB "MOS FLOPPY "
bsFileSystem: 	        DB "FAT12   "

;***************************************
;	Prints a string
;	DS=>SI: 0 terminated string
;***************************************

strTest: db "string", 0

Print:
			lodsb					; load next byte from string from SI to AL
			or			al, al		; Does AL=0?
			jz			PrintDone	; Yep, null terminator found-bail out
			mov			ah,	0eh	; Nope-Print the character
			int			10h
			jmp			Print		; Repeat until null terminator found
PrintDone:
			ret					; we are done, so return

;*************************************************;
;	Bootloader Entry Point
;*************************************************;

loader:

.Reset:
	mov		ah, 0					; reset floppy disk function
	mov		dl, 0					; drive 0 is floppy drive
	int		0x13					; call BIOS
	jc		.Reset					; If Carry Flag (CF) is set, there was an error. Try resetting again

	mov		ax, 0x1000				; we are going to read sector to into address 0x1000:0
	mov		es, ax
	xor		bx, bx

	mov		ah, 0x02				; read floppy sector function
	mov		al, 1					; read 1 sector
	mov		ch, 1					; we are reading the second sector past us, so its still on track 1
	mov		cl, 2					; sector to read (The second sector)
	mov		dh, 0					; head number
	mov		dl, 0					; drive number. Remember Drive 0 is floppy drive.
	int		0x13					; call BIOS - Read the sector
	
	jmp 0x1000:0x0
	
END:
	cli
	hlt


times 510 - ($-$$) db 0						; We have to be 512 bytes. Clear the rest of the bytes with 0

dw 0xAA55							; Boot Signiture

			mov			ah,	0eh	; Nope-Print the character
			mov         al,   't'
			int			10h
			
			cli
			hlt

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# ROM and VGA BIOS images ---------------------------------------------

#romimage:    file=BIOS-bochs-latest, address=0xf0000 
#vgaromimage: VGABIOS-lgpl-latest 

# boot from floppy using our disk image -------------------------------

floppya: 1_44=../os/image-floppy.img, status=inserted  # Boot from drive A

# logging and reporting -----------------------------------------------

log:         OSDev.log             # All errors and info logs will output to OSDev.log
error:       action=report 
info:        action=report