more instructions for bootloader for a FAT12 file system

Author: 0xZangetsueth

README.md

@@ -1 +1 @@
-Understanding low level programming in C and Assembly through system programming : building an OS from scratch
+Understanding low level programming in C and Assembly through system programming : building an OS from scratch (thanks to youtube series from @nanobyte)

build/bootloader.bin

@@ -0,0 +1,35 @@
+bdb_oem: db 'MSWIN4.1': This defines a label bdb_oem followed by a data declaration (db). It assigns the ASCII string "MSWIN4.1" to this label. This is typically used to identify the OEM or operating system associated with the bootloader.
+
+bdb_bytes_per_sector: dw 512: This declares a label bdb_bytes_per_sector followed by a data declaration (dw). It assigns the value 512 to this label, representing the number of bytes per sector in the file system.
+
+bdb_sectors_per_cluster: db 1: This declares a label bdb_sectors_per_cluster followed by a data declaration (db). It assigns the value 1 to this label, representing the number of sectors per cluster in the file system.
+
+bdb_reserved_sectors: dw 1: This declares a label bdb_reserved_sectors followed by a data declaration (dw). It assigns the value 1 to this label, indicating the number of reserved sectors in the file system.
+
+bdb_fat_count: db 2: This declares a label bdb_fat_count followed by a data declaration (db). It assigns the value 2 to this label, specifying the number of File Allocation Tables (FATs) in the file system.
+
+bdb_dir_entries_count: dw 0E0h: This declares a label bdb_dir_entries_count followed by a data declaration (dw). It assigns the value 0E0h (hexadecimal) to this label, representing the number of directory entries or file entries in the root directory.
+
+bdb_total_sectors: dw 2880: This declares a label bdb_total_sectors followed by a data declaration (dw). It assigns the value 2880 to this label, indicating the total number of sectors in the file system.
+
+bdb_media_descriptor_type: db 0F0h: This declares a label bdb_media_descriptor_type followed by a data declaration (db). It assigns the value 0F0h (hexadecimal) to this label, representing the media descriptor type for the floppy disk.
+
+bdb_sectors_per_fat: dw 9: This declares a label bdb_sectors_per_fat followed by a data declaration (dw). It assigns the value 9 to this label, indicating the number of sectors per FAT in the file system.
+
+bdb_sectors_per_track: dw 18: This declares a label bdb_sectors_per_track followed by a data declaration (dw). It assigns the value 18 to this label, representing the number of sectors per track on the storage device.
+
+bdb_heads: dw 2: This declares a label bdb_heads followed by a data declaration (dw). It assigns the value 2 to this label, indicating the number of heads or surfaces on the storage device.
+
+bdb_hidden_sectors: dd 0: This declares a label bdb_hidden_sectors followed by a data declaration (dd). It assigns the value 0 to this label, representing the number of hidden sectors before the partition.
+
+bdb_large_sector_count: dd 0: This declares a label bdb_large_sector_count followed by a data declaration (dd). It assigns the value 0 to this label, indicating the large sector count for the file system.
+
+ebr_drive_number: db 0: This declares a label ebr_drive_number followed by a data declaration (db). It assigns the value 0 to this label, representing the drive number (0 for floppy, 0x80 for HDD).
+
+ebr_signature: db 12h, 34h, 56h, 78h: This declares a label ebr_signature followed by a data declaration (db). It assigns the byte sequence 12h, 34h, 56h, 78h to this label, which can be used as a signature or identification.
+
+ebr_volume_id: db 'ARIA OS': This declares a label ebr_volume_id followed by a data declaration (db). It assigns the ASCII string "ARIA OS" to this label, representing the volume ID or name.
+
+ebr_system_id: db 'FAT12': This declares a label ebr_system_id followed by a data declaration (db). It assigns the ASCII string "FAT12" to this label, indicating the file system type.
+
+start: jmp main: This is the start label followed by an unconditional jump instruction that transfers control to the main label. It serves as the entry point for the execution of the bootloader.

build/kernel.bin

@@ -4,20 +4,32 @@ bits 16
 %define ENDL 0x0D, 0x0A
 
 
-# FAT12 header
+;FAT12 header
 
 jmp short start
 nop
 
-bdb_oem:                 db 'MSWIN4.1'         ; 8bytes
-bdb_bytes_per_sector:    dw 512
-bdb_sectors_per_cluster: db 1
-bdb_reserved_sectors:    dw 1
-
-
-
-
-
+;all of these are explicated in docs/bootloader.md
+bdb_oem:                    db 'MSWIN4.1'         ; 8bytes
+bdb_bytes_per_sector:       dw 512
+bdb_sectors_per_cluster:    db 1
+bdb_reserved_sectors:       dw 1
+bdb_fat_count:              db 2
+bdb_dir_entries_count:      dw 0E0h
+bdb_total_sectors:          dw 2880               ; 2880 * 512 = 1.44MB
+bdb_media_descriptor_type:  db 0F0h               ; F0 = 3.5*  floppy disk
+bdb_sectors_per_fat:        dw 9                  ; 9 sectors/fat
+bdb_sectors_per_track:      dw 18
+bdb_heads:                  dw 2
+bdb_hidden_sectors:         dd 0
+bdb_large_sector_count:     dd 0
+
+;extended boot record
+ebr_drive_number:           db 0                  ; 0x00 floppy, 0x80 hdd
+                            db 0                  ; reserved
+ebr_signature:              db 12h, 34h, 56h, 78h ; serial number
+ebr_volume_id:              db 'ARIA OS'          ; 11 bytes
+ebr_system_id:              db 'FAT12'            ; 8 bytes
 
 
 start: