cpu 8086
org 0x0000

%macro push8086 0
  push ss
  push es
  push ds
  push di
  push si
  push bp
  push sp
  push bx
  push dx
  push cx
  push ax

  ; adjust stored SP to be value before interrupt
  mov bp, sp
  mov [bp+08], bp
  add WORD [bp+08], 28
%endmacro

%macro pop8086 0
  pop ax
  pop cx
  pop dx
  pop bx
  add sp, 2 ; skip SP
  pop bp
  pop si
  pop di
  pop ds
  pop es
  add sp, 2 ; skip SS
%endmacro

rom:
  db 0x55, 0xAA
.sectors:
  db 0x00
.init:
  jmp init
  nop

.name:
  db "RDOS DEBUG", 0

  times (0x18 - ($-$$)) db 0
.pcir_ptr:
  dw 0

  times (0x1A - ($-$$)) db 0
.pnp_ptr:
  dw pnp

pnp:
  db "$PnP"
.version:
  db 1 ; version 1
.length:
  db 2 ; 2 * 16 length
  dw 0 ; offset of next header
  db 0
.checksum:
  db 0 ; checksum (filled by fix-rom)
  dd 0 ; device identifier
  dw 0 ; manufacturer string
  dw rom.name ; product name string
  db 0,0,0 ; device type string
  db 0x20 ; device indicator, bit for "read cacheable" set
  dw 0 ; boot connection vector
  dw 0 ; boot disconnect vector
  dw 0 ; bootstrap entry point
  dw 0 ; reserved
  dw 0

init:
  mov bx, 0
  mov dx, isr_divide_error
  call hook_int

  mov bx, 1
  mov dx, isr_singlestep
  call hook_int

  mov bx, 2
  mov dx, isr_nmi
  call hook_int

  mov bx, 3
  mov dx, isr_breakpoint
  call hook_int

  mov bx, 4
  mov dx, isr_overflow
  call hook_int

  ; 5 left out

  mov bx, 6
  mov dx, isr_invalid_opcode
  call hook_int

  push cs
  pop ds
  mov si, rom.name
  push cs
  push si
  call printf
  db "%S %X", 0x0A, 0x0D, 0
  add sp, 4

  retf

; Hook interrupt
hook_int:
  ; bx times 4
  add bx, bx
  add bx, bx
  ; store offset
  mov [bx], dx
  ; store segment
  push ax
  mov ax, cs
  mov [bx+2], ax
  pop ax
  ret

putc:
  push bx
  push cx
  mov ah, 0x0e
  mov bx, 0x0000
  int 0x10
  pop cx
  pop bx
  ret

; Names for words in debug frame
; Two characters per word, 14 words total
debug_frame_names:
  ; general-purpose registers
  db "AXCXDXBXSPBPSIDI"
  ; extra registers
  db "DSESSSIPCSFL"

; Names for bits in debug_frame+26 (FL/Flags register)
; One character per bit, 16 bits total
debug_frame_flags:
  db "++++ODIT"
  db "SZ+A+P+C"

; Print a single register from the frame
; in	SI	frame offset for register
debug_frame_register_print:
  mov bx, debug_frame_names
  mov al, [cs:bx+si] ; first name char load
  call putc
  mov al, [cs:bx+si+1] ; second name char load
  call putc
  mov al, '='
  call putc
  mov ax, [ss:bp+si] ; value load
  ; prepare call to print_number
  push bx
  push cx
  mov bx, 0x0010
  mov cx, 3
  call print_number_padded
  pop cx
  pop bx
  mov al, ' '
  call putc
  ret

debug_frame_print:
  mov si, 0
  mov cx, 8
.reg1loop:
  call debug_frame_register_print
  add si, 2
  loop .reg1loop

  mov dx, [ss:bp+26]
  mov di, debug_frame_flags
  mov cx, 0x0010
.flag_loop:
  mov al, [cs:di]
  inc di
  cmp al, '+'
  je .next
  test dx, 0x8000
  jnz .write
  mov al, '-'
.write:
  call putc
.next:
  sal dx, 1
  loop .flag_loop

  call printf
  db 0x0A, 0x0D, 0

  mov si, 16
  mov cx, 5
.reg2loop:
  call debug_frame_register_print
  add si, 2
  loop .reg2loop

  call printf
  db 0x0A, 0x0D, 0

  ret

isr_divide_error:
  push8086

  call printf
  db 0x0A, 0x0D, "INT 0 - DIVIDE ERROR", 0x0A, 0x0D, 0

  call debug_frame_print

  jmp halt

isr_singlestep:
  push8086

  call printf
  db 0x0A, 0x0D, 0

  call debug_frame_print

  ; wait for keypress
  xor ax, ax
  int 0x16

  ; enable trace flag so we fire again after next instruction
  or word [ss:bp+26], 0x0100

  pop8086
  iret

isr_nmi:
  push8086

  call printf
  db 0x0A, 0x0D, "INT 2 - NON-MASKABLE INTERRUPT", 0x0A, 0x0D, 0

  call debug_frame_print

  jmp halt

isr_breakpoint:
  push8086

  call printf
  db 0x0A, 0x0D, 0

  call debug_frame_print

  pop8086
  iret

isr_overflow:
  push8086

  call printf
  db 0x0A, 0x0D, "INT 4 - OVERFLOW", 0x0A, 0x0D, 0

  call debug_frame_print

  jmp halt

isr_invalid_opcode:
  push8086

  call printf
  db 0x0A, 0x0D, "INT 6 - INVALID OPCODE", 0x0A, 0x0D, 0

  call debug_frame_print

  jmp halt

halt:
  call printf
  db "HALTED", 0x0A, 0x0D, 0
.loop:
  hlt
  jmp halt

%include "printf.asm"

align 512