i want to compile a boot sector code from bootloader.asm to bootloader.bin using masm. But it is throwing error "must be in segment block". can't we use segmentation in boot loader code if not then what is the solution for the error "must be in segment block".
I am using following command to compile boot loader code:
MASM myboot.asm
after which i can use LINK to generate bin file.
My boot sector code is as given below:
JMP START
NOP
bsOEM_NAME DB 'MSDOS5.0' ; 8 bytes
bsBYTES_PER_SECTOR DW ?
bsSECTORS_PER_CLUSTER DB ?
bsRESERVED_SECTORS DW ?
bsFAT_COPIES DB ?
bsROOT_DIR_ENTRIES DW ?
bsTOTAL_DISK_SECTORS DW ?
bsMEDIA_DESCRIPTOR DB ?
bsSECTORS_PER_FAT DW ?
bsSECTORS_PER_TRACK DW ?
bsSIDES DW ?
bsHIDDEN_SECTORS_HIGH DW ?
bsHIDDEN_SECTORS_LOW DW ?
bsTOTAL_NUM_SECTORS DD ?
bsPHYS_DRIVE_NUMBER_1 DB ?
bsPHYS_DRIVE_NUMBER_2 DB ?
bsBOOT_RECORD_SIG DB 29h
bsVOL_SERIAL_NUM DD 1F61A800h
bsVOLUME_LABEL DB 'NO NAME ' ; 11 bytes
bsFILE_SYSTEM_ID DB 'FAT16 ' ; 8 bytes
;Disk Parameter Block
; The DPB is located in the ROM BIOS at the address pointed to
;by 0078h.
; The 11 bytes starting from START are overwritten at COPY_DPB
;with the
; DPB (7C3E-7C48). This is what the area looks like *after*
;the copy
; at COPY_DPB:
;
START CLI ; Disable interrupts
XOR AX,AX ; AX=0000
MOV SS,AX ; SS=0000
MOV SP,7C00 ; SP grows in decrements
PUSH SS
POP ES ; ES=0000
MOV BX,0078 ; The address of the ROM
; BIOS disk table is 78h.
; (INT 18h). ROM routine
; copies this address during
; cold boot initialization.
LDS SI,[BX] ; SI points to ROMBIOS table
; The source for the copy
PUSH DS
PUSH SI
PUSH SS
PUSH BX
MOV DI,START ; Address of destination
MOV CX,000B ; Size of area to copy
; (Disk parameters)
CLD ; Set direction flag to inc
REPZ ; Move 11 bytes from the
; disk parameter area to
; overlap with the start
; of the code at 7D3E
; (save space?)
MOVSB
PUSH ES
POP DS ; DS=0000
MOV BYTE PTR [DI-02],0F
; At this point, DI points
; to 7C49, one byte after
; the last thing copied.
; Destination operand is
; dpbHEAD_SETTLE_TIME.
MOV CX,bsSECTORS_PER_TRACK
MOV [DI-07],CL ; Destination operand is
; dpbSECTORS_PER_TRACK.
MOV [BX+02],AX ; Destination operand is
; dpbMOTOR_OFF_DELAY.
MOV WORD PTR [BX],START
STI ; The code at 7C6B installs
; the new Int 1E into the
; interrupt table at
; 0000:0078. At 7C68, AX is
; 0. START is the offset
; for the new INT 1E.
INT 13 ; Reset drives (AX=0000)
JB ERROR_IN_BOOT_1
XOR AX,AX
CMP bsTOTAL_DISK_SECTORS,AX
JZ LOOP_1
MOV CX,bsTOTAL_DISK_SECTORS
MOV bsTOTAL_NUM_SECTORS,CX
LOOP_1 MOV AL,bsFAT_COPIES
MUL WORD PTR bsSECTORS_PER_FAT
ADD AX,bsHIDDEN_SECTORS_HIGH
ADC DX,bsHIDDEN_SECTORS_LOW
ADD AX,bsRESERVED_SECTORS
ADC DX,+00
MOV [7C50],AX
MOV [7C52],DX
MOV [7C49],AX
MOV [7C4B],DX
MOV AX,0020
MUL WORD PTR bsROOT_DIR_ENTRIES
MOV BX,bsBYTES_PER_SECTOR
ADD AX,BX
DEC AX
DIV BX
ADD [7C49],AX
ADC WORD PTR [7C4B],+00
MOV BX,0500 ; Buffer for root directory
MOV DX,[7C4B]
MOV AX,[7C49]
CALL CALCULATE
JB ERROR_IN_BOOT_1
MOV AL,01
CALL READ_SECTOR
JB ERROR_IN_BOOT_1 ;Error? Print message
; and reboot.
MOV DI,BX
MOV SI,OFFSET FILE_IO_SYS
REPZ
CMPSB
JNZ ERROR_IN_BOOT_1 ;First file in root
; dir is not IO.SYS?
; Print error.
LEA DI,[BX+20]
MOV CX,000B ; 11 characters in DOS
; filename.
REPZ
CMPSB ; Is second file in root
; MSDOS.SYS?
JZ LOOP_2 ; Yes? Then continue on.
ERROR_IN_BOOT_1 MOV SI,OFFSET NON_SYSTEM_DISK
CALL WRITE_STRING
XOR AX,AX
INT 16
POP SI
POP DS
POP [SI]
POP [SI+02]
INT 19
ERROR_IN_BOOT_2 POP AX
POP AX
POP AX
JMP ERROR_IN_BOOT_1
LOOP_2 MOV AX,[BX+1A]
DEC AX
DEC AX
MOV BL,SECTORS_PER_CLUSTER
XOR BH,BH
MUL BX
ADD AX,[7C49]
ADC DX,[7C4B]
MOV BX,0700 ; DOS loading buffer
MOV CX,0003
LOOP_3 PUSH AX
PUSH DX
PUSH CX
CALL CALCULATE
JB ERROR_IN_BOOT_2
MOV AL,01
CALL READ_SECTOR
POP CX
POP DX
POP AX
JB ERROR_IN_BOOT_1
ADD AX,0001
ADC DX,+00
ADD BX,BYTES_PER_SEC
LOOP LOOP_3
MOV CH,MEDIA_DESCRIPTOR
MOV DL,PHYS_DRIVE_NUMBER_1
MOV BX,[7C49]
MOV AX,[7C4B]
JMP 0070:0000 ; Transfer to ROM BIOS
WRITE_STRING LODSB
OR AL,AL
JZ RETURN_FROM_2
MOV AH,0E
MOV BX,0007
INT 10
JMP WRITE_STRING
CALCULATE CMP DX,SECTORS_PER_TRACK
JNB RETURN_FROM_1
DIV WORD PTR SECTORS_PER_TRACK
INC DL
MOV [7C4F],DL
XOR DX,DX
DIV WORD PTR SIDES
MOV PHYS_DRIVE_NUMBER_2,DL
MOV [7C4D],AX
CLC
RET
RETURN_FROM_1 STC
RETURN_FROM_2 RET
READ_SECTOR MOV AH,02 ; 02h is ReadSector .
MOV DX,[7C4D] ; DH is head/side number.
; DL is drive number.
; (Bit 7 of DL set for HD)
MOV CL,06 ; CL is sector number.
SHL DH,CL ; Multiply DH (number of
; heads) by 6.
OR DH,[7C4F]
MOV CX,DX
XCHG CH,CL
MOV DL,bsPHYS_DRIVE_NUMBER_1
MOV DH,bsPHYS_DRIVE_NUMBER_2
INT 13 ; ReadSector
RET
NON_SYSTEM_DISK DB 13,10
DB 'Non-System disk or disk error'
DB 13,10
DB 'Replace and press any key when ready'
DB 13,10,0
FILE_IO_SYS DB 'IO SYS'
FILE_MSDOS_SYS DB 'MSDOS SYS'
DB 0,0,55,AA
