initial commit

.editorconfig

@@ -0,0 +1,10 @@
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+insert_final_newline = true
+
+[{*.s,Makefile}]
+indent_style = tab
+indent_size = 8

LICENSE

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+Copyright © 2025 Niklas Elsbrock
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the “Software”), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Makefile

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+src_dir := src
+build_dir := build
+
+asm := nasm
+
+qemu := qemu-system-i386
+qemu_flags := -drive file=$(build_dir)/rainbowboot.img,format=raw
+qemu_flags_gdb := -s -S
+
+dosbox := dosbox
+
+.PHONY: all run run-gdb run-dosbox attach clean
+
+all: $(build_dir)/rainbowboot.img
+
+run: $(build_dir)/rainbowboot.img
+	$(qemu) $(qemu_flags)
+
+run-gdb: $(build_dir)/rainbowboot.img
+	$(qemu) $(qemu_flags_gdb) $(qemu_flags)
+
+run-dosbox: $(build_dir)/rainbowboot.img
+	$(dosbox) -c "BOOT $(build_dir)/rainbowboot.img"
+
+attach: $(build_dir)/rainbowboot.elf
+	gdb $(build_dir)/rainbowboot.elf \
+		-ex "target remote localhost:1234" \
+		-ex "set architecture i8086"
+
+clean:
+	rm -rf $(build_dir)
+
+$(build_dir)/rainbowboot.img: $(build_dir)/rainbowboot.elf | $(build_dir)
+	objcopy -O binary $(build_dir)/rainbowboot.elf $(build_dir)/rainbowboot.img
+
+$(build_dir)/rainbowboot.elf: $(build_dir)/rainbowboot.o | $(build_dir)
+	ld -Ttext=0x7c00 -melf_i386 $(build_dir)/rainbowboot.o -o $(build_dir)/rainbowboot.elf
+
+$(build_dir)/rainbowboot.o: $(src_dir)/rainbowboot.s | $(build_dir)
+	$(asm) -f elf32 -g3 -F dwarf $(src_dir)/rainbowboot.s -o $(build_dir)/rainbowboot.o
+
+$(build_dir):
+	mkdir -p $(build_dir)

README.md

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+# rainbowboot
+
+This is a x86 boot sector demo that prints a rolling rainbow pattern to screen.
+
+Licensed under 
+
+## How to use
+
+Make sure you have NASM (and QEMU, GDB and DOSBox if applicable) installed.
+
+### Building the disk image
+
+```sh
+make
+```
+
+### Running on QEMU
+
+```sh
+make run
+```
+
+### Running on DOSBox
+
+```sh
+make run-dosbox
+```
+
+### Debugging using QEMU and GDB
+
+Starting QEMU in debug mode:
+
+```sh
+make run-gdb
+```
+
+Attaching to the virtual machine:
+
+```sh
+make attach
+```

src/rainbowboot.s

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+%define	CHAR	'#'		; printed ASCII character
+%define	DELAY	40000		; time delay between lines in microseconds
+%define	CCOUNT	7		; amount of colors
+;; colors (see https://en.wikipedia.org/wiki/BIOS_color_attributes):
+%define	COLORS	0x04, 0x0C, 0x0E, 0x0A, 0x0B, 0x09, 0x05
+
+%define	DELAY_L	(DELAY & 0xFFFF)
+%define	DELAY_H	(DELAY >> 16)
+
+bits 16
+
+section .text
+	global _start
+
+_start:
+	cli			; disable hardware interrupts
+	xor	bh, bh		; set page number to 0
+	mov	ax, 0x0003	; set video mode
+	int	0x10		; --- interrupt
+	mov	ah, 0x01	; hide cursor
+	mov	ch, 0x3F	; --- ...
+	int	0x10		; --- interrupt
+	mov	ah, 0x02	; move cursor to bottom
+	mov	dh, 24		; --- row 24
+	xor	dl, dl		; --- column 0
+	int	0x10		; --- interrupt
+	xor	si, si		; set color index to 0
+.loop	mov	ah, 0x09	; print 80 colored characters
+	mov	cx, 80		; --- set count to 80
+	mov	al, CHAR	; --- set character
+	mov	bl, [colors+si]	; --- set attribute (color)
+	int	0x10		; --- interrupt
+	mov	ah, 0x86	; sleep
+	mov	cx, DELAY_H	; --- set microseconds (cx:dx)
+	mov	dx, DELAY_L	; --- ...
+	int	0x15		; --- interrupt
+	mov	ah, 0x0E	; print line feed
+	mov	al, 0x0A	; --- set character to line feed
+	int	0x10		; --- interrupt
+	inc	si		; increment color index
+	cmp	si, CCOUNT	; --- if color index is inside bounds
+	jl	.loop		; --- -> repeat loop
+	xor	si, si		; --- else, set color index to 0
+	jmp	.loop		; repeat loop
+
+colors:	db	COLORS
+
+	times	510 - ($ - $$) db 0
+	dw	0xAA55