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feat(boot): read BPB

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d0p1 🏳️‍⚧️ 2024-07-29 16:40:21 +02:00
parent 85d09cbbf6
commit 899e456249
4 changed files with 63 additions and 1 deletions
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1
boot/common/const.inc
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@ -16,6 +16,7 @@ STACK_TOP = 0x7000
; ---------- Magic ------------
STPDBOOT_MAGIC = 0x53545044
STPDFS_MAGIC = 0x44505453
; ---------- Video ------------
VIDEO_WIDTH = 1024

17
boot/common/fat12.inc
View file

@ -1,5 +1,22 @@
;; File: fat12.inc
struc fat_bpb
{
.jump db 3 dup(?)
.oem_name db 8 dup(?)
.bytes_per_sects dw ?
.sects_per_clust db ?
.reserved_sects dw ?
.FAT_count db ?
.root_dir_entries dw ?
.total_sects dw ?
.media_type db ?
.sects_per_FAT dw ?
.sects_per_track dw ?
.heads_per_cyl dw ?
}
defn fat_bpb
;; Struct: fat_entry
struc fat_entry
{

7
boot/loader/disk.inc
View file

@ -1,4 +1,11 @@
;; File: disk.inc
;; Function: disk_read_sectors
;;
;; In:
;; AX - LBA starting sector
;; CX - Sector count
;; ES:BX - buffer
disk_read_sectors:
; test byte [bDriveLBA], TRUE
; je .lba_read

37
boot/loader/loader.asm
View file

@ -65,7 +65,44 @@ _start:
; 0 512 1024 XXXX XXXX
;
; read stupidfs super block
mov ax, DISK_BUFFER/0x10
mov es, ax
mov ax, 1
mov cx, 1
xor bx, bx
call disk_read_sectors
cmp dword [DISK_BUFFER], STPDFS_MAGIC
jne .fat_fallback
; fallback to fat12
; for now fat12 is asumed
.fat_fallback:
; get bpb
mov ax, DISK_BUFFER/0x10
mov es, ax
xor bx, bx
mov ax, 0
mov cx, 1
call disk_read_sectors
mov word ax, [DISK_BUFFER + fat_bpb.sects_per_track]
mov word [sectors_per_track], ax
mov word ax, [DISK_BUFFER + fat_bpb.heads_per_cyl]
mov word [heads_per_cylinder], ax
mov word ax, [DISK_BUFFER + fat_bpb.bytes_per_sects]
mov word [bytes_per_sector], ax
mov word ax, [DISK_BUFFER + fat_bpb.sects_per_FAT]
mov word [sectors_per_FAT], ax
mov byte al, [DISK_BUFFER + fat_bpb.FAT_count]
mov byte [FAT_count], al
mov word ax, [DISK_BUFFER + fat_bpb.reserved_sects]
mov word [reserved_sectors], ax
mov word ax, [DISK_BUFFER + fat_bpb.root_dir_entries]
mov word [root_dir_entries], ax
mov byte al, [DISK_BUFFER + fat_bpb.sects_per_clust]
mov byte [sectors_per_cluster], al
call fat_load_root