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‎.gitignore

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build/*.img
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build/*.iso

‎Makefile

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NASM = nasm
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QEMU = qemu-system-i386
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QEMU_DRIVE = a
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NAME = retrokern
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FILENAME = $(NAME).img
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IMAGE = build/$(FILENAME)
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ISO_IMAGE = build/iso/$(FILENAME)
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ISO = build/$(NAME).iso
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ISO_DIR = build/iso
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BOOT = src/boot.asm
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all: $(IMAGE)
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$(IMAGE): $(BOOT)
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$(NASM) -isrc/ -f bin -o $(IMAGE) $(BOOT)
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floppy:
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dd bs=512 count=2880 if=/dev/zero of=$(ISO_IMAGE)
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dd status=noxfer conv=notrunc if=$(IMAGE) of=$(ISO_IMAGE)
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iso:
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$(MAKE) floppy
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genisoimage -quiet -V 'FLOPPYBIRD' -input-charset iso8859-1 -o $(ISO) -b $(FILENAME) $(ISO_DIR)
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clean:
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rm -f $(IMAGE)
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rm -f $(ISO_IMAGE)
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rm -f $(ISO)
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‎README.md

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Retrokern
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=========
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Retrokern is a 16-bit x86 assembly-based "operating system" that aims to accomplish the following goals:
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* Provide a teaching platform for x86 assembly
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* Provide a simple non-DOS, completely free operating system for retro projects
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This system requires absolutely no operating system and will boot (in theory) in any 8086 or later CPU, including modern x86_64 systems.
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Copyright
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---------
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Written by Robert W. Oliver II <[email protected]>
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Copyright (C) 2018 Sourcerer, All Rights Reserved.
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License
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-------
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Licensed under the GPLv3.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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Thanks
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------
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Retrokern was inspired and borrows some code from Mihail Szabolcs's FloppyBird DOS/Assembly game.
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https://github.com/icebreaker/floppybird/
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The author would like to thank Sourcerer for inspiration, support, and promotion.

‎build/.gitkeep

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‎build/iso/.gitkeep

Whitespace-only changes.

‎misc/dosbox.conf

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[cpu]
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cycles=10000

‎src/boot.asm

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%define SECTORS 16
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%define IMAGE_SIZE ((SECTORS + 1) * 512) ; SECTORS + 1 (~= 18) * 512 bytes
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%define STACK_SIZE 256 ; 4096 bytes in paragraphs
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; Declare 16-bit mode
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bits 16
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; Boot sector entry point
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;org 0x7C00
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start:
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cli ; disable interrupts
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;
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; Notes:
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; 1 paragraph = 16 bytes
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; 32 paragraphs = 512 bytes
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;
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; Skip past our SECTORS
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; Skip past our reserved video memory buffer (for double buffering)
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; Skip past allocated STACK_SIZE
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;
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mov ax, (((SECTORS + 1) * 32) + 4000 + STACK_SIZE)
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mov ss, ax
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mov sp, STACK_SIZE * 16 ; 4096 in bytes
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sti ; enable interrupts
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mov ax, 07C0h ; point all segments to _start
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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; dl contains the drive number
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mov ax, 0 ; reset disk function
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int 13h ; call BIOS interrupt
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jc disk_reset_error
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push es ; save es
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mov ax, 07E0h ; destination location (address of _start)
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mov es, ax ; destination location
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mov bx, 0 ; index 0
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mov ah, 2 ; read sectors function
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mov al, SECTORS ; number of sectors
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mov ch, 0 ; cylinder number
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mov dh, 0 ; head number
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mov cl, 2 ; starting sector number
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int 13h ; call BIOS interrupt
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jc disk_read_error
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pop es ; restore es
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mov si, boot_msg ; boot message
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call _puts ; print
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jmp 07E0h:0000h ; jump to _start (a.k.a stage 2)
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disk_reset_error:
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mov si, disk_reset_error_msg
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jmp fatal
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disk_read_error:
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mov si, disk_read_error_msg
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fatal:
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call _puts ; print message in [DS:SI]
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mov ax, 0 ; wait for a keypress
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int 16h
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mov ax, 0 ; reboot
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int 19h
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; _puts - in-boot-sector put string function
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; pointer in SI
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_puts:
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lodsb ; move byte [DS:SI] into AL
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; is this the end of the string?
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cmp al, 0
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je .end
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; display character BIOS call
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mov ah, 0x0E
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int 0x10
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; move to next character
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jmp _puts
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.end:
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ret
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disk_reset_error_msg: db 'Disk reset error.',0
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disk_read_error_msg: db 'Disk read error.',0
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boot_msg: db 'Booting Retrokern... ', 0
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; Pad to 510 bytes, then 2 more magic bytes to fill the boot sector
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times 510 - ($ - $$) db 0
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dw 0xAA55
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; entry point
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_start:
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call main ; call main
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jmp $ ; loop forever
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%include 'console.asm';
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%include 'timer.asm'
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%include 'speaker.asm'
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%include 'video.asm'
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%include 'core.asm'
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; main.asm contains the main loop
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%include 'main.asm'
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; pad to IMAGE_SIZE
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times IMAGE_SIZE - ($ - $$) db 0

‎src/console.asm

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; getchar()
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; Returns keyboard press in AX
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getchar:
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pusha
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mov ax, 0x0
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int 0x16
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mov [.chr], ax
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popa
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mov ax, [.chr]
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ret
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.chr: dw 0
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; kbhit - returns key hit in AX (without wait)
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kbhit:
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pusha
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mov al, 0 ; check for any keys hit
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mov ah, 1 ; but do not block (async)
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int 16h ; call BIOS interrupt
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jz .end ; if no keys hit jump to end
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mov ax, 0 ; get key hit function
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int 16h ; call BIOS interrupt
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mov [.key], ax
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popa
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mov ax, [.key]
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ret
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.end:
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popa
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mov ax, 0 ; set AX to 0 if no keys hit
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ret
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.key: dw 0
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‎src/core.asm

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; Reboot the system
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reboot:
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mov ax, 0x0
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int 0x19
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ret
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‎src/main.asm

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main:
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call set_text_mode
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.start:
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.reboot:
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call reboot
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ret
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