cpu 8086
org 0x0
jmp init

isr_dos_main:
  cmp ah, 0x01
  je isr_getc_echo
  cmp ah, 0x02
  je isr_putc
  cmp ah, 0x25
  je isr_intr_register
  jmp isr_invalid

%include "intr.asm"
%include "chario.asm"

; ISR for invalid subfunctions or unimplemented
isr_invalid:
  mov bp, 0xFEFE
  int3
.hlt:
  hlt
  jmp .hlt
; ISR tail to set carry flag to signal error
isr_error:
  push bp
  mov bp, sp
  ; set carry flag
  or WORD [SS:BP+6], 1
  pop bp
isr_return:
  iret

%include "drive.asm"

init:
  mov ax, cs
  mov ds, ax
  mov es, ax

  mov di, kernel_end
  call drive_setup

  mov dx, isr_dos_main
  mov ax, 0x2521
  pushf
  push cs
  call isr_dos_main

  mov dl, 0x37
  mov ah, 0x02
  int 0x21

  cli
.halt:
  hlt
  jmp .halt


kernel_end: