feat(boot): read BPB

d0p1s4m4 · Jul 29, 2024 · 899e456 · 899e456
1 parent 85d09cb
commit 899e456
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Showing 4 changed files with 63 additions and 1 deletion.
diff --git a/boot/common/const.inc b/boot/common/const.inc
@@ -16,6 +16,7 @@ STACK_TOP      = 0x7000
 
 ; ---------- Magic ------------
 STPDBOOT_MAGIC = 0x53545044
+STPDFS_MAGIC   = 0x44505453
 
 ; ---------- Video ------------
 VIDEO_WIDTH  = 1024

diff --git a/boot/common/fat12.inc b/boot/common/fat12.inc
@@ -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
 {

diff --git a/boot/loader/disk.inc b/boot/loader/disk.inc
@@ -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

diff --git a/boot/loader/loader.asm b/boot/loader/loader.asm
@@ -64,8 +64,45 @@ _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