Fixed paging fully now. Kernel is loaded with virtual memory enabled. Just need to write an allocator and make kernel use virtual memory addresses for its stuff. Restructured codebase to be less messy. Updated Makefile to put binary files under build/ rather than in root directory

2021-10-11 20:47:04 +01:00
parent 6328062d4f
commit 1225529708
18 changed files with 585 additions and 58 deletions
@@ -0,0 +1,141 @@
+[ORG 0x7C00]
+[BITS 16]
+
+jmp short bootcode
+nop
+
+bpOEMid db "XNOE    "
+
+bpBytesPerSector dw 512
+bpSectorsPerCluster db 1
+bpReservedSectors dw 32 ; We should reserve some sectors. Boot sector + stage2
+bpNoFATs db 2
+bpRootDirEntries dw 256
+bpLVSectors dw 8586
+bpMediumID db 0xF8
+bpSectorsPerFat dw 34
+bpSectorsPerTrack dw 18
+bpHeads dw 2
+bpHiddenSectors dw 0
+
+TIMES 36 - ($ - $$) db 0
+
+bpDriveNo db 0
+db 0
+bpSignature db 0x29
+bpVolumeID dd 0x0
+bpVolumeLabel db "XNOE OS    "
+bpFileSystem db "FAT16   "
+
+bootcode:
+
+  mov byte [bpDriveNo], dl
+
+  ; Get the disk configuration from the BIOS
+  mov ah, 08h
+  int 13h
+
+  add dh, 1
+  movzx dx, dh
+  mov word [bpHeads], dx
+  and cl, 03fh
+  movzx cx, cl
+  mov word [bpSectorsPerTrack], cx
+
+  ; Load the stage2 (32-bit) from the next sectors
+  ; Load it at 0x7e00
+  mov ax, 7e0h
+  mov es, ax
+  xor bx, bx
+
+  mov ax, 2 ; Begin with the 2nd sector
+  call prep_i13
+  mov al, 31 ; Load the next 9 sectors (4.5k)
+  int 13h
+
+  ; We need to get the memory configuration from the BIOS now
+  ; To do this we can use int 15h eax=e820h
+  ; We will load the e820 data to 0x20000
+
+  mov ax, 2000h
+  mov es, ax
+  xor di, di
+  xor ebx, ebx
+
+get_memory_map_loop:
+  mov edx, 0x534D4150
+  mov ecx, 24
+
+  mov eax, 0xe820
+  int 15h
+  jc mmap_finish
+
+  cmp ebx, 0
+  je mmap_finish
+
+  add di, 24
+  jmp get_memory_map_loop
+
+mmap_finish:
+  ; Now we should prepare to enter in to protected mode for the sole purpose of running the stage2 bootloader
+
+  ; Enable the A20 line
+  in al, 0x92
+  or al, 2
+  out 0x92, al
+
+  ; Load the temporary GDT
+  cli
+  lgdt [gdt_desc]
+  mov eax, cr0
+  or eax, 1
+  mov cr0, eax
+
+  jmp 08h:7e00h ; Far jump to where we loaded the stage 2
+
+; In ax with sector addr, out correct values for int 13h
+prep_i13:
+  xor dx, dx
+  div word [bpSectorsPerTrack]
+
+  push dx
+
+  xor dx, dx
+  div word [bpHeads]
+
+  mov ch, al
+  mov dh, dl
+  mov dl, byte [bpDriveNo]
+
+  pop ax
+  mov cl, al
+
+  mov al, 1
+  mov ah, 2
+
+  ret
+
+gdt:
+null:
+  dq 0
+code:
+  dw 0xffff
+  dw 0
+  db 0
+  db 10011010b
+  db 11001111b
+  db 0
+data:
+  dw 0xffff
+  dw 0
+  db 0
+  db 10010010b
+  db 11001111b
+  db 0
+gdt_end:
+gdt_desc:
+  dw gdt_desc - gdt_end - 1
+  dd gdt
+
+TIMES 510 - ($ - $$) db 0
+DW 0xAA55