create test bootloader

Makefile

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+ASM=nasm
+
+SRC_DIR=src
+BUILD_DIR=build
+
+BOOT_FILES 		= $(shell find $(SRC_DIR)/boot/ -type f -name "*.asm")
+KERN_ASM_FILES 	= $(shell find $(SRC_DIR)/kernel/ -type f -name "*.asm")
+
+BOOT_BIN_FILES 	= $(patsubst src/%.asm, $(BUILD_DIR)/%.bin, $(BOOT_FILES))
+KERN_BIN_FILES 	= $(patsubst src/%.asm, $(BUILD_DIR)/%.bin, $(KERN_ASM_FILES))
+
+BOOTLOADER 		= $(BUILD_DIR)/boot.bin
+KERNEL 			= $(BUILD_DIR)/kernel.bin
+IMAGE			= $(BUILD_DIR)/clipper.img
+
+.PHONY: all clipper kernel bootloader clean always
+
+clipper: $(IMAGE)
+
+$(IMAGE): bootloader kernel
+	dd if=/dev/zero of=$(IMAGE) bs=512 count=2880
+	mkfs.fat -F 12 -n "CLPR" $(IMAGE)
+	dd if=$(BOOTLOADER) of=$(IMAGE) conv=notrunc
+	mcopy -i $(IMAGE) $(KERNEL) "::kernel.bin"
+
+bootloader: $(BOOT_BIN_FILES)
+	cp $(BUILD_DIR)/boot/boot.bin $(BOOTLOADER)
+
+kernel: $(KERN_BIN_FILES)
+	cp $(BUILD_DIR)/kernel/kernel.bin $(KERNEL)
+
+$(BUILD_DIR)/%.bin: $(SRC_DIR)/%.asm
+	@mkdir -p "$(@D)"
+	$(ASM) $< -f bin -o $@
+
+clean:
+	rm -rf $(BUILD_DIR)/*

README.md

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+# Clipper
+
+Clipper is an operating system kernel I write to learn about kernel development. As of right now, it is more or less following [nanobyte's](https://www.youtube.com/@nanobyte-dev) OS development tutorial.
+
+My ultimate goal is to create a simple, bootable POSIX-compliant operating system.

bochs_config

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+megs: 128
+romimage: file=/usr/share/bochs/BIOS-bochs-latest, address=0xfffe0000
+vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
+floppya: 1_44=build/clipper.img, status=inserted
+boot: floppy
+mouse: enabled=0
+display_library: sdl, options="gui_debug"
+

src/boot/boot.asm

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+org 0x7C00
+bits 16
+
+%define ENDL 0x0D, 0x0A
+
+; FAT 12 BIOS PARAMETER BLOCK
+jmp short start
+nop
+bpb_oem:					db "CLPROS01"
+bpb_bytes_per_sector:		dw 512
+bpb_sectors_per_cluster:	db 1
+bpb_reserved_sectors:		dw 1
+bpb_fat_count:				db 2
+bpb_dir_entries_count:		dw 0E0h
+bpb_total_sectors:			dw 2880
+bpb_media_descriptor_type:	db 0F0h
+bpb_sectors_per_fat:		dw 9
+bpb_sectors_per_track:		dw 18
+bpb_heads:					dw 2
+bpb_hidden_sectors:			dd 0
+bpb_large_sector_count:		dd 0
+
+; EXTENDED BOOT RECORD
+ebr_drive_number:			db 0
+							db 0
+ebr_signature:				db 28h
+ebr_volume_id:				db 63h, 6Ch, 70h, 72h
+ebr_volume_label:			db "Clipper    "
+ebr_system_identifier:		db "FAT12   "
+
+start:
+	jmp main
+
+;
+; Prints a string to the screen
+; Params:
+;	- ds:si points to string
+puts:
+	push si
+	push ax
+
+	mov ah, 0Eh
+
+.loop:
+	lodsb		; load byte at ds:si into al
+	or al, al	; is null?
+	jz .done
+
+	int 10h
+	jmp .loop
+
+.done:
+	pop si
+	pop ax
+	ret
+	
+
+main:
+	; setup data segment
+	mov ax, 0
+	mov ds, ax
+	mov es, ax
+
+	; setup stack
+	mov ss, ax
+	mov sp, 0x7C00
+
+	; print message
+	mov si, msg_hello
+	call puts
+
+	; read something from disk
+	mov [ebr_drive_number], dl
+	mov ax, 1
+	mov cl, 1
+	mov bx, 0x7E00
+	call disk_read
+
+	mov di, 0
+	mov cl, [ebr_drive_number]
+.loop:
+	xor ch, ch
+	shl cx, 4
+	add ch, 30h
+	test cx, 9
+	jle .write_disk_number
+	add ch, 11h 
+
+.write_disk_number:
+	mov byte [msg_drive_number_value + di], ch
+	inc di
+	cmp di, 2
+	jne .loop
+
+	mov si, msg_drive_number
+	call puts
+
+	hlt
+	jmp halt
+
+floppy_error:
+	mov si, msg_read_failed
+	call puts
+	jmp wait_key_and_reboot
+	
+wait_key_and_reboot:
+	mov ah, 0
+	int 16h
+	jmp 0FFFFh:0 
+	hlt
+
+halt:
+	cli
+	hlt
+
+;
+; Convert LBA address to CHS
+; Parameters:
+;	- ax: LBA address
+; Returns:
+;	- cx [bits 0-5]: sector
+;	- cx [bits 6-15]: cylinder
+;	- dh: head
+;
+lba_to_chs:
+	push ax
+	push dx
+
+	xor dx, dx
+	div word [bpb_sectors_per_track]
+
+	inc dx
+	mov cx, dx
+
+	xor dx, dx
+	div word [bpb_heads]
+
+	mov dh, dl
+	mov ch, al
+	shl ah, 6
+	or cl, ah
+
+	pop ax
+	mov dl, al
+	pop ax
+	ret
+
+;
+; Reads from disk
+; Parameters:
+; 	- ax: LBA address
+;	- cl: number of sectors to read (max 128)
+;	- dl: drive number
+;	- es:bx: memory address where to store data
+;
+disk_read:
+	push ax
+	push bx
+	push cx
+	push dx
+	push di
+
+	push cx
+	call lba_to_chs
+	pop ax
+
+	mov ah, 02h
+	mov di, 3
+
+.retry:
+	pusha
+	stc 
+	int 13h
+	jnc .done
+
+	popa
+	call disk_reset
+
+	dec di
+	jnz .retry
+
+.fail:
+	jmp floppy_error
+
+.done:
+	popa
+
+	pop di
+	pop dx
+	pop cx
+	pop bx
+	pop ax
+	ret
+
+;
+; Resets a disk controller
+; Parameters:
+;	dl: drive number
+;
+disk_reset:
+	pusha
+	mov ah, 0
+	stc
+	int 13h
+	jc floppy_error
+	popa
+	ret
+
+
+msg_hello: 				db "Hello, Clipper!", ENDL, 0
+msg_read_failed:		db "Failed to read from disk.", ENDL, 0
+msg_drive_number:		db "Disk number: "
+msg_drive_number_value: dw 0
+msg_drive_number_end:	db ENDL, 0
+
+times 510-($-$$) db 0
+dw 0AA55h