rdos/kernel/main.asm

cpu 8086

; Memory layout (starting from top)
%define self    0xF000

; A single sector for disk i/o
%define diskbuf (self-0x200)

; BYTE sectors/track and BYTE number of sides
; 4 times for A: B: C: and D:
%define chstab  (diskbuf - (4*2))

; DWORD partition offset for C: and D:
%define parttab (chstab - (2*4))

%define stack   (parttab)

org self
jmp init

banner:
  db "RDOS 2019-09", 0x0A, 0x0D, 0

print_banner:
  mov cl, 2
  mov si, banner
.loop:
  mov dl, BYTE [si]
  test dl, dl
  jz .end
  call cpm_syscall
  inc si
  jmp .loop
.end:
  ret

init:
  mov sp, stack

  call print_banner

  mov si, init_program
  call exec

  cli
.halt:
  hlt
  jmp .halt

init_program:
  db "HELLO.COM", 0

cpm_syscall:
  cmp cl, 0x02
  je putc
  stc
  ret

putc:
  push ax
  push bx
  mov al, dl
  mov ah, 0x0e
  mov bx, 0x0000
  int 0x10
  pop bx
  pop ax
  ret

%include "exec.asm"
%include "fcb.asm"