cpu 8086
org 0x0100
jmp init

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

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

%include "cache.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

init:
  push cs
  pop es
  mov di, isr_dos_main
  mov ax, 0x21
  call intr_register

  mov di, kernel_end
  call cache_init

  int3

  cli
.halt:
  hlt
  jmp .halt

kernel_end: