Disk reading partly done
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; Reset the disk system using int 13h / AH = 00h
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disk_reset:
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pusha
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stc
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mov ah, 00h
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int 13h
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popa
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ret
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; ------------------------------------
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; Load the root directory into memory (into disk_buffer which is 24000h)
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disk_load_root:
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pusha
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mov ax, 19 ; First sector of root entry
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call math_lba_to_chs ; Assigns ch, cl and dh the correct values
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xor ax,ax
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mov dl, [ebr_drive_number] ; Drive number
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mov ah, 02h ; BIOS ah code for read disk sectors to memory
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mov al, 0Ch ; Root directory has 12 sectors
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mov si, root_buffer ; ES:BX should point to our buffer
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mov bx, si
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; repeat drive read 3 times (incase of random error)
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mov di, 3 ; counter
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; This is basically
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; for di in range(3,1,1):
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; We test to see if we can read the disk 3 times
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.try_read_disk: ; Try read the floppy three times
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; When the disk is tried to be read, the CF flag will be
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; set if there's an error, so we just clear it to return it to
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; the default state
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stc ; sets the cf flag
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int 13h
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jnc .done_read ; jump if cf = 0
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call disk_reset ; Reset drivers of disk
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dec di ; di -= 1
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test di, di ; if di = 0
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jnz .try_read_disk
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jmp .disk_error
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.disk_error:
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mov si, disk_read_fail
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call os_print_string
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popa
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ret
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.done_read:
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popa
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ret
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; ---------------------------------------------
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; Reads a certain number of sectors into memory
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; int 13h/ah = 02h read disk sectors into memory
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; al = number of sectors to read
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; ch = cylinder number
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; cl = sector number
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; dh = head number
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; dl = drive number
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; es:bx = points to data buffer
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disk_read:
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push ax
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push bx
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push cx
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push dx
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push di
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; cl = sector
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; ch = cylinder
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; dh = head
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; dl = drive
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call math_lba_to_chs ; Get the chs address
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mov ah, 02h ; BIOS ah code for read disk sectors to memory
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; repeat drive read 3 times (incase of random error)
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mov di, 3 ; counter
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; This is basically
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; for di in range(3,1,1):
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; We test to see if we can read the disk 3 times
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.retry:
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; When the disk is tried to be read, the CF flag will be
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; set if there's an error, so we just clear it to return it to
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; the default state
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stc ; sets the cf flag
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int 13h
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jnc .done_read ; jump if cf = 0
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call .disk_reset ; Reset drivers of disk
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dec di ; di -= 1
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test di, di ; if di = 0
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jnz .retry
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.fail_disk_read:
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pop di
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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; int 13h / ah = 00h reset disk system
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.disk_reset:
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pusha
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mov ah, 0 ; Reset drive
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stc
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int 13h
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jc .fail_disk_read
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popa
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ret
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.done_read:
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pop di
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pop dx
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pop cx
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pop bx
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pop ax
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ret
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; -------------------------------------
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disk_load_file:
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pusha
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mov di, fat12_file_name
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call os_format_fat_filename
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; Prepare values
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mov si, root_buffer
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xor bx,bx
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.search_root:
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mov di, fat12_file_name ; Move the name of the kernel into di
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mov cx, 11 ; length of 'KERNEL BIN'
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push si ; Preserve si
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repe cmpsb ; Repeat a comparison of bytes between file name and current bytes until it finds a match
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pop si ; Retrieve si
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je .found_file
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add si, 32 ; increment di to the next directory entry
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inc bx
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cmp bx, [bdb_dir_entries_count] ; Have we reached the number of directories that exist
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jl .search_root ; Repeat search
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jmp .file_not_found ; If the last dir has been searched, then there is no kernel
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.found_file:
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mov ax, [si+26] ; ax is now a pointer to the pointer to the file relative to the data segments :D
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add ax, 20h
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mov [file_cluster], ax
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; Setup registers for disk read
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mov bx, data_buffer
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mov dl, [ebr_drive_number]
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call disk_read ; Load file from disk into memory
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jmp .done
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.file_not_found:
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mov si, file_not_found
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call os_print_string
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jmp .done
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.done:
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popa
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ret
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section .data:
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disk_read_fail: db 'Error: Could not read disk\n', 0
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file_not_found: db 'File not found\n', 0
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file_found: db 'File found\n', 0
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loading_root: db 'Loading root diretory\n', 0
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file_cluster: dw 0
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fat12_file_name: db ' '
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