; BIOS puts our boot sector at 0000:7c00
org 0x7c00  
; We're (probably) in real mode
bits 16 

  ; Disable interrupts, fuck knows what an interrupt would do right now
  cli

  xor ax, ax

  mov ds, ax
  mov es, ax

  ; Put the stack base at the address of our program text (stack will grow high->low away from it).
  ; We're not doing anything with a stack right now but who knows we might want to later
  mov ss, ax
  mov sp, 0x7c00

  ; Segment for VGA (0xb800 * 16 = 0xb8000)
  mov ax, 0xb800
  mov fs, ax

  mov ah, 0x00
  mov al, 0x03
  int 0x10

  ; Hi!
  mov word fs:[0x0000], 0xc048
  mov word fs:[0x0002], 0xc069
  mov word fs:[0x0004], 0xc021

  hlt

  ; TODO: grab all the info we can from bios interrupts and deliver it to ths OS nicely
  ; e.g. in a fixed memory location

  ; TODO:
  ; - Generate GPT in justfile
  ; - Parse global parition table
  ; - Load second stage from GPT partition with a particular UUID / name like GRUB does
  ;   (it's Hah!IdontNeedEFI in GRUB)
  ;   - https://en.wikipedia.org/wiki/BIOS_boot_partition
  ; - Future work:
  ;   - Boot from UEFI
  ;   - Boot on non-GPT partitioned disk

  ; MBR bootstrap field is 440 bytes long
  %if ($ - $$) > 440
  %error "exceeded mbr bootstrap field size"
  %endif

  ; Pad to the end of the MBR bootstrap field
  times 440 - ($ - $$) db 0

  ; Unique disk ID
  dd 0x00000000
  ; Reserved
  dw 0x0000

  ; Zero the partition fields
  ; TODO: fill in the field pointing to the GPT table
  times 510 - ($ - $$) db 0

  ; Boot signature
  db 0x55
  db 0xaa