; ============================================================================
;
; Install Litos System on Floppy
;
; ============================================================================
; ------------- Setup parameters
DISK EQU 0 ; booting disk (0=diskette A:)
HEADS EQU 2 ; number of heads
SECTORS EQU 18 ; number of sectors per track
; ------------- Start of program
SECTION .text
BITS 16
org 100h ; start of COM program
; ------------- Prepare address of disk buffer (cannot overlap 64 KB boundary)
Start: mov ax,ds ; AX <- program segment
shl ax,1
shl ax,1
shl ax,1
shl ax,1 ; AX * 16
add ax,[Sector] ; add current buffer offset
add ax,200h ; test buffer overlapping
jnc BufferOK ; buffer is OK
mov ax,[Sector] ; AX <- current buffer address
add ax,200h ; move over boundary
mov [Sector],ax ; new buffer address
; ------------- Open file with boot sector
BufferOK: mov ax,3d00h ; AX <- function (open for reading)
mov dx,Filename ; DX <- name of file with boot sector
int 21h ; open file for reading
jnc OpenOK ; file open OK
; ------------- Error - file not found
mov dx,FoundErr ; DX <- error message
Error: mov ah,9 ; AH <- function code
int 21h ; display error message
int 20h ; end of program
; ------------- Read file into memory (AX=file identifier)
OpenOK: mov bx,ax ; BX <- file identifier
mov cx,512 ; CX <- length of boot sector
mov dx,[Sector] ; DX <- buffer for reading sector
mov ah,3fh ; AH <- function code
int 21h ; read sector into memory
; ------------- Close file
mov ah,3eh ; AH <- function code
int 21h ; close file
; ------------- Displays prompt text for user
mov ah,9 ; AH <- function code
mov dx,Message ; DX <- message to display
int 21h ; display message
; ------------- Waiting for a key
mov ax,0c08h ; AX <- function code
int 21h ; waiting for a key
cmp al,27 ; is it Esc key?
jne InitDisk ; it is not Esc, start write
int 20h ; end of program
; ------------- Display message - Writing sector
InitDisk: mov ah,9 ; AH <- function code
mov dx,StartText ; DX <- text to display
int 21h ; display message
; ------------- Open file with program
mov ax,3d00h ; AX <- function (open for reading)
mov dx,Filename2 ; DX <- name of file with boot sector
int 21h ; open file for reading
mov dx,FoundErr2 ; DX <- error message
jc Error ; error - file not found
mov bx,ax ; BX <- file identifier
; ------------- Determine file size
mov ax,4202h ; AX <- function (seek to end of file)
xor cx,cx ; CX <- 0 offset HIGH
xor dx,dx ; DX <- 0 offset LOW
int 21h ; determine file size -> DX:AX
; ------------- Convert file size to number of sectors (multiple of 512 Bytes)
add ax,511 ; round up to nearest sector
adc dx,0 ; overflow
mov al,ah ; AL <- file size / 256 (LOW)
mov ah,dl ; AH <- file size / 256 (HIGH)
shr ax,1 ; AX = file size in sectors
mov si,[Sector] ; SI <- buffer
; ------------- Filling up setup parameters
mov [si+3],ax ; number of sectors to read
mov byte [si+5],DISK ; booting disk
mov byte [si+6],HEADS ; number of heads
mov byte [si+7],SECTORS ; number of sectors per track
; ------------- Write boot sector
call Write ; write boot sector
; ------------- Reset file pointer
push ax ; push AX
mov ax,4200h ; AH <- function (seek to begin of file)
xor cx,cx ; CX <- 0 offset HIGH
xor dx,dx ; DX <- 0 offset LOW
int 21h ; reset file pointer
pop ax ; pop AX
; ------------- Read next sector of program
CopyProg: push ax ; push AX (number of sectors)
mov cx,512 ; CX <- length of boot sector
mov dx,[Sector] ; DX <- buffer for reading sector
mov ah,3fh ; AH <- function code
int 21h ; read sector into memory
pop ax ; pop AX (number of sectors)
; ------------- Write sector of program
call Write ; write sector of program
dec ax ; number of sectors
jnz CopyProg ; copy next sector of program
; ------------- Close file
mov ah,3eh ; AH <- function code
int 21h ; close file
; ------------- All OK
mov ah,9 ; AH <- function code
mov dx,AllOKText ; DX <- message "All OK"
int 21h ; display message
int 20h ; end of program
; ----------------------------------------------------------------------------
; Procedure - write 1 sector
; ----------------------------------------------------------------------------
; ------------- Push registers
Write: push ax ; push AX
push bx ; push BX
push cx ; push CX
push dx ; push DX
push si ; push SI
; ------------- Prepare registers
mov si,3 ; number of attempts
WriteAgain: mov cl,[WriteSector] ; CL <- write sector
mov dh,[WriteHead] ; DH <- write head
mov ch,[WriteTrack] ; CH <- write track
mov dl,DISK ; DL <- disk
mov bx,[Sector] ; BX <- buffer with sector
mov ax,301h ; AH <- function, AL <- num. of sectors
push ds ; push DS to stack
pop es ; ES <- DS data segment
push si ; push attempt counter
int 13h ; write sector
pop si ; pop attempt counter
jnc Write2 ; operation OK
; ------------- Error - reset disk and try again (maybe disk change)
mov ah,0 ; AH <- function code
int 13h ; reset disk system
dec si ; attempt counter
jnz WriteAgain ; next attempt
; ------------- Error - cannot write to a floppy
mov ah,9 ; AH <- function code
mov dx,WriteErr ; DX <- error message
int 21h ; display error message
add sp,6*2 ; delete registers and return address
int 20h ; end of program
; ------------- Shift write pointers
Write2: mov al,[WriteSector] ; AL <- write sector
inc ax ; increase sector number
cmp al,SECTORS ; is it valid sector?
jbe Write4 ; it is valid sector
mov al,1 ; AL <- 1 new sector number
mov ah,[WriteHead] ; AH <- write head
inc ah ; increase head number
cmp ah,HEADS ; is it valid head?
jb Write3 ; it is valid head
mov ah,0 ; AH <- 0 new head number
inc byte [WriteTrack] ; new track number
Write3: mov [WriteHead],ah ; new write head
Write4: mov [WriteSector],al ; new write sector
; ------------- Pop registers
pop si ; pop SI
pop dx ; pop DX
pop cx ; pop CX
pop bx ; pop BX
pop ax ; pop AX
ret
; ------------- Messages
FoundErr db "ERROR: File BOOT\BOOT.BIN not found!",13,10,"$"
FoundErr2 db "ERROR: File LITOS.SYS not found!",13,10,"$"
WriteErr db "ERROR: Cannot write to disk!",13,10,"$"
Message db "Insert formated disk into A: and press",13,10
db "any key to continue or Esc to abort...",13,10,"$"
StartText db "Writing sectors...",13,10,"$"
AllOKText db "All OK",13,10,"$"
; ------------- Write pointers
WriteSector db 1 ; write sector
WriteHead db 0 ; write head
WriteTrack db 0 ; write track
; ------------- Files
Filename db "BOOT\BOOT.BIN",0
Filename2 db "LITOS.SYS",0
; ------------- Buffer of boot sector
Sector dw Buffer
Buffer:
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