From ed9d22fb423f92be45e0f6c3d695728970376035 Mon Sep 17 00:00:00 2001
From: Xnoe <xnoe@xnoe.moe>
Date: Sun, 29 Aug 2021 06:58:12 +0100
Subject: [PATCH] We now have FAT16 file loading support in the bootloader.

---
 boot.asm | 149 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 134 insertions(+), 15 deletions(-)

diff --git a/boot.asm b/boot.asm
index d3c023a..d065b37 100644
--- a/boot.asm
+++ b/boot.asm
@@ -1,23 +1,133 @@
 [BITS 16]  ;tell the assembler that its a 16 bit code
 
-mov ax, 7c0h
-mov ds, ax
+jmp short bootcode
+nop
 
-mov si, _boot_msg
-call _boot_print
+bpOEMid db "XNOE    "
+bpBytesPerSector dw 512
+bpSectorsPerCluster db 1
+bpReservedSectors dw 1
+bpNoFATs db 2
+bpRootDirEntries dw 256
+bpLVSectors dw 8419
+bpMediumID db 0F0h
+bpSectorsPerFat dw 9
+bpSectorsPerTrack dw 18
+bpSides dw 2
+bpHiddenSectors dd 0
+bpLargeSectors dd 0
+bpDriveNo dw 0
+bpSignature db 41
+bpVolumeID dd 00000000h
+bpVolumeLabel db "XNOE OS    "
+bpFileSystem db "FAT16   "
 
-mov ah, 02h
-mov al, 1
-mov ch, 0
-mov cl, 2
-mov dh, 0
+bootcode:
+  mov ax, 7c0h
+  mov ds, ax
 
-mov bx, 2000h
-mov es, bx
-xor bx, bx
-int 13h
+  mov byte [drive], dl
 
-jmp 2000h:0
+  mov si, boot_msg
+  call _boot_print
+
+  mov ax, ds
+  mov es, ax
+  mov bx, buffer
+
+  mov ah, 2
+  mov al, 16
+  mov cl, 20
+  mov ch, 0
+  mov dh, 0
+  mov dl, byte [drive]
+
+  int 13h
+
+  mov cx, [bpRootDirEntries]
+  mov di, buffer
+
+  mov ax, 0
+
+;  jmp $
+
+kernel_finder:
+  xchg cx, dx
+
+  mov di, buffer
+  add di, ax
+
+;  mov si, di
+;  call _boot_print
+;  mov si, new_line
+;  call _boot_print
+
+  mov si, kernel_file
+  mov cx, 11
+  rep cmpsb
+  je kernel_found
+
+  add ax, 20h
+
+  xchg cx, dx
+  loop kernel_finder
+
+  mov si, kernel_nf
+  call _boot_print
+
+  jmp $
+
+kernel_found:
+  mov ax, [es:di+0fh]
+  mov word [cluster], ax
+
+fat_loader:
+  mov ax, ds
+  mov es, ax
+  mov bx, buffer
+
+  mov ah, 2
+  mov al, 9
+  mov cl, 2
+  mov ch, 0
+  mov dh, 0
+  mov dl, byte [drive]
+
+  int 13h
+
+kernel_loader:
+  mov ax, 2000h
+  mov es, ax
+  mov bx, word [pointer]
+
+  mov al, byte [cluster]
+  mov word [buffer+20h], ax
+
+  add al, 34
+
+  mov cl, al
+  mov al, 1
+  mov ah, 2
+  mov ch, 0
+  mov dh, 0
+  mov dl, byte [drive]
+
+  int 13h
+
+  add word [pointer], 512
+
+  mov si, word [cluster]
+  add si, buffer
+  add si, 1
+  cmp word [si], 0ffffh
+  je kernel_loaded
+
+  add word [cluster], 1
+  jmp kernel_loader
+
+kernel_loaded:
+  mov dword [buffer], 0xdeadbeef
+  jmp 2000h:0h
 
 _boot_print:
   mov ah, 0eh
@@ -32,7 +142,16 @@ _boot_print_loop:
 _boot_print_exit:
   ret
 
-_boot_msg db "Boot Sector OK!", 13, 10, 0
+boot_msg db "Boot Sector OK!", 13, 10, 0
+kernel_nf db "KERNEL.BIN Missing!", 13, 10, 0
+new_line db " ", 0
+kernel_file db "KERNEL  BIN"
+
+cluster dw 0
+pointer dw 0
+drive db 0
 
 TIMES 510 - ($ - $$) db 0    ;fill the rest of sector with 0
 DW 0xAA55          ; add boot signature at the end of bootloader
+
+buffer:
\ No newline at end of file