rdos/kernel/dosapi.asm

isr_dosmain:
  cmp ah, 0x01
  je isr_getc_echo
  cmp ah, 0x02
  je isr_putc
  iret

isr_getc_echo:
  mov ah, 0x00
  int 0x16
  cmp al, 0x00
  je isr_getc_echo
  iret

isr_putc:
  mov al, dl
  call putc
  iret