jurjen.ladeniusandClaude Opus 4.8
f3340e86c6
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
155 lines
3.2 KiB
NASM
155 lines
3.2 KiB
NASM
BDOS = 0xF37D
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_DIRIO = 0x06
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_DIRIN = 0x07
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_FOPEN = 0x0F
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_SETDTA = 0x1A
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_RDBLK = 0x27
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org 0xC01E
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boot_start:
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ret nc
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ld (0xC059), de ; Address to jump after MSXDOS.SYS execution
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ld (buffer), a ; ????
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ld (hl), 0x56 ; Write 0xC056 (callback_addr) at address pointed by HL
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inc hl
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ld (hl), 0xC0
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loading_start:
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ld sp, 0xF51F ; Set callstack address
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ld de, fcb_start
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ld c, _FOPEN ; Open file (FCB)
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call BDOS ; Open MSXDOS.SYS
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inc a
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jp z, handle_error ; If open failed
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ld de, 0x0100
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ld c, _SETDTA ; Set disk transfer address
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call BDOS
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ld hl, 0x0001
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ld (fcb_record), hl ; Record size
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ld hl, 0x3F00 ; Number of records to read (16128 bytes! Max size?)
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ld de, fcb_start ; Pointer to opened FCB
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ld c, _RDBLK ; Random block read (FCB)
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call BDOS
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jp 0x0100 ; Execute MSXDOS.SYS
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callback_addr:
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ld e, b
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ret nz
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call 0x0000 ; Call the address set in DE at startup
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ld a, c
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and 0xFE
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cp 0x02
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jp nz, label_01
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handle_error:
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ld a, (buffer)
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and a
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jp z, 0x4022
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label_01:
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ld de, error_message
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call print_str
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ld c, _DIRIN ; Direct console input
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call BDOS ; Wait for key press
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jr loading_start ; Retry loading MSXDOS.SYS
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print_str: ; Print null-terminted string in DE address
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ld a, (de)
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or a
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ret z ; Return from print_str
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push de
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ld e, a
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ld c, _DIRIO ; Direct console I/O
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call BDOS
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pop de
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inc de
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jr print_str
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error_message:
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db 0x42 ;'B'
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db 0x6F ;'o'
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db 0x6F ;'o'
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db 0x74 ;'t'
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db 0x20 ;' '
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db 0x65 ;'e'
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db 0x72 ;'r'
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db 0x72 ;'r'
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db 0x6F ;'o'
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db 0x72 ;'r'
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db 0x0D ;''
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db 0x0A ;''
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db 0x50 ;'P'
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db 0x72 ;'r'
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db 0x65 ;'e'
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db 0x73 ;'s'
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db 0x73 ;'s'
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db 0x20 ;' '
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db 0x61 ;'a'
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db 0x6E ;'n'
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db 0x79 ;'y'
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db 0x20 ;' '
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db 0x6B ;'k'
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db 0x65 ;'e'
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db 0x79 ;'y'
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db 0x20 ;' '
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db 0x66 ;'f'
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db 0x6F ;'o'
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db 0x72 ;'r'
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db 0x20 ;' '
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db 0x72 ;'r'
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db 0x65 ;'e'
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db 0x74 ;'t'
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db 0x72 ;'r'
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db 0x79 ;'y'
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db 0x0D ;''
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db 0x0A ;''
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db 0x00 ;
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fcb_start:
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db 0x00 ; 00 Drive number. 0=default drive
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db 0x4D ; 01 'M' Filename
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db 0x53 ; 02 'S'
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db 0x58 ; 03 'X'
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db 0x44 ; 04 'D'
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db 0x4F ; 05 'O'
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db 0x53 ; 06 'S'
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db 0x20 ; 07 ' '
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db 0x20 ; 08 ' '
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db 0x53 ; 09 'S' Extension
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db 0x59 ; 0A 'Y'
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db 0x53 ; 0B 'S'
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db 0x00 ; 0C Extent number (low byte)
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db 0x00 ; 0D File attributes
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fcb_record:
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db 0x00 ; 0E Record size (low byte) / Extent number (high byte)
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db 0x00 ; 0F Record size (high byte)
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db 0x00 ; 10 File size (32 bits)
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db 0x00 ; 11
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db 0x00 ; 12
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db 0x00 ; 13
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db 0x00 ; 14 Volume-id (32 bits)
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db 0x00 ; 15
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db 0x00 ; 16
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db 0x00 ; 17
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db 0x00 ; 18 Internal information
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db 0x00 ; 19
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db 0x00 ; 1A
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db 0x00 ; 1B
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db 0x00 ; 1C
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db 0x00 ; 1D
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db 0x00 ; 1E
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db 0x00 ; 1F
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db 0x00 ; 20 Current record within extent
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db 0x00 ; 21 Random record number
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db 0x00 ; 22
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db 0x00 ; 23
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db 0x00 ; 24
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buffer:
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db 0x00 ; |