83 lines
2.6 KiB
ArmAsm
83 lines
2.6 KiB
ArmAsm
; Copyright 2022 Mattia Giambirtone & Contributors
|
|
;
|
|
; Licensed under the Apache License, Version 2.0 (the "License");
|
|
; you may not use this file except in compliance with the License.
|
|
; You may obtain a copy of the License at
|
|
;
|
|
; http://www.apache.org/licenses/LICENSE-2.0
|
|
;
|
|
; Unless required by applicable law or agreed to in writing, software
|
|
; distributed under the License is distributed on an "AS IS" BASIS,
|
|
; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
; See the License for the specific language governing permissions and
|
|
; limitations under the License.
|
|
|
|
; Definition of the MBR (Master Boot Record). This is basically our bootloader and
|
|
; is located in the first 512 bytes of the drive we're booting from. From here, we
|
|
; do some basic setup and then call into the kernel
|
|
|
|
[org 0x7c00] ; Address where the code expects to be loaded in. The BIOS always loads us here
|
|
kernel_offset: equ 0x1000
|
|
|
|
; We save the value of the current boot drive
|
|
mov [boot_drive], dl
|
|
|
|
; Now we setup the stack by setting the
|
|
; base pointer to address 0x9000. The address
|
|
; itself doesn't matter as long as it's far
|
|
; enough away from memory already in use by
|
|
; the BIOS
|
|
mov bp, 0x9000
|
|
mov sp, bp
|
|
call bios_cls
|
|
mov si, real_mode_msg
|
|
call bios_println
|
|
call load_kernel
|
|
call switch_to_protected_mode
|
|
jmp $ ; Keeps jumping at the current address (loops forever)
|
|
|
|
|
|
; Now we include our "function definitions" (after the
|
|
; loop, so they're never executed unless explicitly called)
|
|
%include "src/boot/util/disk.s"
|
|
%include "src/boot/util/io.s"
|
|
%include "src/boot/gdt.s"
|
|
%include "src/boot/switch32.s"
|
|
|
|
|
|
; Here we define our variables: They need to be defined after the
|
|
; halting because otherwise they will be executed as code
|
|
real_mode_msg: db "TSOS is starting up", 0
|
|
protected_mode_msg: db "Switched to protected mode", 0
|
|
loading_kernel_msg: db "Loading kernel into memory", 0
|
|
boot_drive: db 0
|
|
|
|
|
|
[bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code
|
|
load_kernel: ; Loads the kernel into memory
|
|
mov si, loading_kernel_msg
|
|
call bios_println
|
|
mov bx, kernel_offset
|
|
mov dh, 3
|
|
mov dl, [boot_drive]
|
|
call load_disk
|
|
ret
|
|
|
|
|
|
[bits 32]
|
|
BEGIN_32BIT: ; After the switch we will get here
|
|
mov esi, protected_mode_msg
|
|
; My modified print function takes an offset
|
|
; to add to the start of the video memory that
|
|
; is added before writing. We skip the first
|
|
; 320 bytes so that we don't overwrite the log
|
|
; messages we have already written
|
|
mov ecx, 0x140
|
|
call vga_print
|
|
call kernel_offset
|
|
jmp $
|
|
|
|
; Padding and magic number
|
|
times 510 - ($-$$) db 0
|
|
dw 0xaa55
|