Improvements and code conveniance : mbr
This commit is contained in:
Adrien Bourmault
parent
eac19a8ac7
commit
bcff95e6d0
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bin/disk.img
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bin/disk.img
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bin/mbr.bin
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bin/mbr.bin
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obj/boot/mbr.bin
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obj/boot/mbr.bin
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@ -9,6 +9,25 @@
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;=----------------------------------------------------------------------------=;
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%define TRAM 0x0B8000 ; [T]ext[RAM]
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%define VRAM 0x0A0000 ; [V]ideo[RAM]
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%define OEMName bp+0x03 ; Disk label
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%define bytesPerSector bp+0x0b ; Bytes per sector
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%define sectorsPerCluster bp+0x0d ; Sectors per cluster
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%define reservedSectors bp+0x0e ; Reserved sectors
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%define fats bp+0x10 ; Number of fats
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%define rootDirEntries bp+0x11 ; Number of entries in root dir
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%define sectors bp+0x13 ; Logical sectors
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%define mediaType bp+0x15 ; Media descriptor byte
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%define fatSectors bp+0x16 ; Sectors per FAT
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%define sectorsPerTrack bp+0x18 ; Sectors per track
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%define heads bp+0x1a ; Number of sides/heads
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%define hiddenSectors bp+0x1c ; Hidden sectors
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%define hugeSectors bp+0x20 ; LBA sectors
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%define biosBootdrvNum bp+0x24 ; Bootdrv number
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%define reserved bp+0x25 ; This is not used
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%define bootSignature bp+0x26 ; Bootdrv signature
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%define volumeId bp+0x27 ; Volume ID
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%define volumeLabel bp+0x2b ; Volume Label
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%define fatTypeLabel bp+0x36 ; File system type
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[BITS 16]
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[ORG 0x1000]
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@ -26,9 +26,9 @@
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[BITS 16] ; Ensure 16-bit code (because fuck UEFI)
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;---------------------------------------------------
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; Disk description table
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;---------------------------------------------------
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;---------------------------------------------------;
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; Disk description table ;
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;---------------------------------------------------;
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Intro:
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jmp short _start ; Jump over the BIOS PARAMETER BLOCK
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@ -60,7 +60,7 @@ _start:
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jmp BOOT_SEG:$+5 ; Fix the cs:ip registers with a vaudou magical trip
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bootstrap:
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jmp bootstrapper
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jmp go
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;; LOVELY DATA
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FileNotFound db "FStage ERR : NO LOADER", 0 ; File was not found
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@ -71,7 +71,7 @@ filename db "LOADER BIN" ; Filename
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;; GO !
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bootstrapper:
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go:
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mov ax, BOOT_SEG ; Set segments to the location of the bootloader
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mov ds, ax
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mov es, ax
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@ -86,11 +86,11 @@ bootstrapper:
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;; INITIALIZE BOOT DISK
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or dl, dl ; Verifying dl points actually to the boot drive
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jz loadRoot
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jz load_root
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mov byte [Bootdrv], dl ; Another soul (the disk) saved !
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mov ah, 0x08
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int 0x13 ; int 0x13 : read drive parameters/geom
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jc loadRoot
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jc load_root
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and cx, 0x003f ; Maximum sector number is the high bits 6-7 of cl
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mov word [sectorsPerTrack], cx ; And whose low 8 bits are in ch
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mov dl, dh ; Convert the maximum head number to a word with another vaudou magical trip
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@ -100,7 +100,7 @@ bootstrapper:
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;; LOAD THE ROOT DIRECTORY FROM DISK
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loadRoot:
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load_root:
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xor cx, cx
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mov ax, 32 ; Size of root dir = (rootDirEntries * 32) / bytesPerSector
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mul word [rootDirEntries] ; multiply by the total size of the root directory
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@ -116,23 +116,23 @@ loadRoot:
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mov di, BUFFER_SEG ; Set the extra segment to the disk buffer
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mov es, di
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mov di, BUFFER_OFF ; Set es:di and load the root directory into the disk buffer
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call readSectors ; Read the sectoooooooors !
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call read_sectors ; Read the sectoooooooors !
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;; FIND THE SECOND STAGE LOADER
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mov di, BUFFER_OFF ; Set es:di to the disk buffer
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mov cx, word [rootDirEntries] ; Search through all of the root dir entries
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xor ax, ax ; Clear ax for the file entry offset
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searchRoot:
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search_root:
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xchg cx, dx ; Save cx because it's a loop counter
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mov si, filename ; Load the filename
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mov cx, 11 ; Compare first 11 bytes
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rep cmpsb ; Compare si and di cx times
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je loadFat ; We found the LOADEEEEEEEER!!!
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je load_fat ; We found the LOADEEEEEEEER!!!
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add ax, 32 ; File entry offset
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mov di, BUFFER_OFF ; Point back to the start of the entry
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add di, ax ; Add the offset to point to the next entry
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xchg dx, cx
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loop searchRoot ; Continue to search for the file
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loop search_root ; Continue to search for the file
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;; ERROR...
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mov si, FileNotFound ; Could not find the file
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@ -153,7 +153,7 @@ reboot:
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int 0x19 ; Reboot the system
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;; LOAD THE FAT FROM THE FILE
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loadFat:
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load_fat:
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mov ax, word [es:di + 15] ; Get the file cluster at offset 26
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push ax ; Store the FAT cluster
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xor ax, ax ; Size of fat = (fats * fatSectors)
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@ -162,15 +162,14 @@ loadFat:
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mov cx, ax ; Store in cx
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mov ax, word [reservedSectors] ; Convert the first fat on the disk
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mov di, BUFFER_OFF ; Set es:di and load the fat sectors into the disk buffer
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call readSectors ; Read the sectooooooooooors !!!
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call read_sectors ; Read the sectooooooooooors !!!
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;; LOAD THE CLUSTERS OF THE LOADER AND JUMP
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loadFile:
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mov di, LOAD_SEG
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mov es, di ; Set es:bx to where the file will load
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mov di, LOAD_OFF
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pop ax ; File cluster restored
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call readClusters ; Read clusters from the file
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call read_clusters ; Read clusters from the file
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mov dl, byte [Bootdrv] ; Pass the boot Bootdrv into dl
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jmp LOAD_SEG:LOAD_OFF ; Jump to the file loaded!
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@ -186,7 +185,7 @@ loadFile:
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; FUNCTIONS ;
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;---------------------------------------------------;
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readClusters:
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read_clusters:
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;---------------------------------------------------;
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; Read file clusters, starting at the given cluster,;
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; expects FAT to be loaded into the disk buffer. ;
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@ -199,13 +198,9 @@ readClusters:
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; Returns: None ;
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; ;
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;---------------------------------------------------;
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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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pusha
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push es
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.clusterLoop:
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.cluster_loop:
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xor bh, bh
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xor dx, dx
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push ax ; Get the cluster start = (cluster - 2) * sectorsPerCluster + UserData
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@ -215,13 +210,13 @@ readClusters:
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add ax, word [UserData] ; add the UserData
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xor ch, ch
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mov cl, byte [sectorsPerCluster] ; Sectors to read
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call readSectors ; Read the sectors
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call read_sectors ; Read the sectors
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pop ax ; Current cluster number
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xor dx, dx
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.calculateNextSector16: ; Get the next sector for FAT16 (cluster * 2)
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;; Calculate next sector for FAT16 (cluster * 2)
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mov bx, 2 ; Multiply the cluster by two (cluster is in ax)
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mul bx
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.loadNextSector:
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;; Load sector in RAM
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push ds
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push si
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mov si, BUFFER_SEG
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@ -231,27 +226,23 @@ readClusters:
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mov ax, word [ds:si] ; Load ax to the next cluster in FAT
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pop si
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pop ds
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.nextSectorCalculated:
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;; Next
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cmp ax, 0xfff8 ; Check if we are at the end of the file?
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jae .done
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add di, 512 ; Add to the pointer offset
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jnc .clusterLoop
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.fixBuffer: ; An error will occur if the buffer in memory
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jnc .cluster_loop
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;; Correct the buffer because an error will occur if the buffer in memory
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mov dx, es ; overlaps a 64k page boundry, when di overflows
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add dh, 0x10 ; it will trigger the carry flag, so correct
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mov es, dx ; extra segment by 0x1000
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jmp .clusterLoop ; Load the next file cluster
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jmp .cluster_loop ; Load the next file cluster
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.done:
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pop es
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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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popa
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ret
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readSectors:
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read_sectors:
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;---------------------------------------------------;
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; Read sectors starting at a given sector by ;
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; the given times and load into a buffer. Please ;
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@ -264,14 +255,10 @@ readSectors:
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; Returns: None ;
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; ;
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;---------------------------------------------------;
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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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pusha
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push es
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mov bx, di ; Convert es:di to es:bx for int 13h
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.sectorLoop:
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.sector_loop:
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push ax
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push cx
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xor dx, dx
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@ -291,35 +278,31 @@ readSectors:
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or cl, ah ; Now cx is set with respective track and sector numbers
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mov dl, byte [Bootdrv] ; Set correct Bootdrv for int 13h
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mov di, 5 ; Try five times to read the sector because i love 5
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.attemptRead:
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.attempt_read:
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mov ax, 0x0201 ; Read Sectors func of int 13h, read one sector
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int 0x13 ; Call int 13h (BIOS disk I/O)
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jnc .readOk ; If no carry set, the sector has been read
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jnc .read_ok ; If no carry set, the sector has been read
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xor ah, ah ; Reset Bootdrv func of int 13h
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int 0x13 ; Call int 13h (BIOS disk I/O)
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dec di ; Decrease read attempt counter
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jnz .attemptRead ; Try to read the sector again
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jnz .attempt_read ; Try to read the sector again
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mov si, DiskError ; Error reading the disk :/
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call print
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jmp reboot
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.readOk:
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.read_ok:
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pop cx
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pop ax
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inc ax ; Increase the next sector to read
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add bx, word [bytesPerSector] ; Add to the buffer address for the next sector
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jnc .nextSector
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.fixBuffer: ; An error will occur if the buffer in memory
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jnc .next_sector
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;; Fixing buffer because an error will occur if the buffer in memory
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mov dx, es ; overlaps a 64k page boundry, when bx overflows
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add dh, 0x10 ; it will trigger the carry flag, so correct
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mov es, dx ; es segment by 0x1000
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.nextSector:
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loop .sectorLoop
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.next_sector:
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loop .sector_loop
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pop es
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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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popa
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ret
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print:
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