nightloader/stage_1/start.asm

STAGE_1_CODE_MEMORY_ADDRESS                 equ 0x7c00
STAGE_1_STACK_MEMORY_ADDRESS                equ 0x07e0

NIGHTLOADER_PARTITION_TYPE                  equ 0x9d

ORIGINAL_PARTITION_TABLE_OFFSET             equ 446
ORIGINAL_NUM_PARTITIONS_IN_TABLE            equ 4
ORIGINAL_PARTITION_ENTRY_SIZE               equ 16

BOOTABLE_BYTE_OFFSET                        equ 0
CHS_START_SECTOR_ADDRESS_OFFSET             equ 1
PARTITION_TYPE_OFFSET                       equ 4
CHS_END_SECTOR_ADDRESS                      equ 5
FIRST_LBA_SECTOR_ADDR_OFFSET                equ 8
LAST_LBA_SECTOR_ADDR_OFFSET                 equ 12

org STAGE_1_CODE_MEMORY_ADDRESS
bits 16
stage_0:
    
    mov bx, STAGE_1_STACK_MEMORY_ADDRESS
    mov ss, bx
    mov bx, 0x0800
    mov bp, 256
    mov sp, 256
    
    mov bx, 0x0000
    mov ds, bx
    mov es, bx
    
    mov di, dx
    
    ; set the video mode correctly
    xor ah, ah          ; bios-function (set video mode)
    mov al, 3           ; video mode with 80x25 characters
    int 0x10
    
    
    
.search_partition:
    
    mov si, STAGE_1_CODE_MEMORY_ADDRESS
    add si, ORIGINAL_PARTITION_TABLE_OFFSET
    mov cx, 0           ; offset of the current entry from the partition table start
    
    
    
.search_loop:
    
    mov bx, si
    add bx, cx
    add bx, PARTITION_TYPE_OFFSET
    
    mov al, [bx]
    
    cmp al, NIGHTLOADER_PARTITION_TYPE
    je .load_partition;
    
    ; go to the next entry
    add cx, ORIGINAL_PARTITION_ENTRY_SIZE
    
    ; check if there are more entries
    cmp dx, ORIGINAL_NUM_PARTITIONS_IN_TABLE * ORIGINAL_PARTITION_ENTRY_SIZE
    jb .search_loop
    jmp .no_boot_partition
    
    
    
.load_partition:
    
    mov si, cx          ; address of the partition table entry of the nightloader-partition
    
    ; TODO: Make this more flexible; that's urgent.
    mov     ah,     0x02            ; action (read from disk)
    mov     al,     8               ; num_sectors
    mov     ch,     0               ; cylinder
    mov     cl,     2               ; sector (starts at 1, max.: 63)
    mov     dx,     di              ; storage device id
    mov     dh,     0               ; head
    mov     bx,     0x0800
    mov     es,     bx              ; read destination segment
    mov     bx,     0x0000          ; read destination address
    int 0x13
    
    mov si, 0x8000
    mov cx, 8
    mov dh, 12
    mov dl, 36
    call print_string
    ; jmp .wait
    
    jmp 0x0800:0x0000
    
    
    

.no_boot_partition:
    
    mov si, errors.no_boot_partition
    mov cx, 30
    mov dl, 25
    mov dh, 12
    call print_string
    
.wait:
    cli
    hlt


MESSAGE_LENGTH_NO_BOOT_PARTITION            equ 30

errors:
.no_boot_partition:
    db "NO NIGHTLOADER-PARTITION FOUND"
.hex:
    db "0123456789abcdef"

%include "utility.asm"
%include "fat32.asm"
%include "partition_table.asm"