first commit

.gitignore

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+*~
+build/*

Makefile

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+ASM=nasm
+
+SRC_DIR=src
+BUILD_DIR=build
+
+.PHONY: all floppy_image kernel bootloader clean always
+
+#
+# Floppy image
+#  * use dd to create 1.44MB blank image file
+#  * apply FAT12 filesystem to image
+#  * copy 512 byte bootloader binary to image using dd (overwriting first sector)
+#  * copy kernel binary to filesystem
+#    + this step wtill fail if bootloader binary does not contain proper FAT12 headers
+#
+floppy_image: $(BUILD_DIR)/main_floppy.img
+
+$(BUILD_DIR)/main_floppy.img: bootloader kernel
+	dd if=/dev/zero of=$(BUILD_DIR)/main_floppy.img bs=512 count=2880
+	mkfs.fat -F 12 -n "WEESLOS" $(BUILD_DIR)/main_floppy.img
+	dd if=$(BUILD_DIR)/bootloader.bin of=$(BUILD_DIR)/main_floppy.img conv=notrunc
+	mcopy -i $(BUILD_DIR)/main_floppy.img $(BUILD_DIR)/kernel.bin "::kernel.bin"
+
+#
+# Bootloader
+#
+bootloader: $(BUILD_DIR)/bootloader.bin
+
+$(BUILD_DIR)/bootloader.bin: always
+	$(ASM) $(SRC_DIR)/bootloader/boot.asm -f bin -o $(BUILD_DIR)/bootloader.bin
+
+#
+# Kernel
+#
+kernel: $(BUILD_DIR)/kernel.bin
+
+$(BUILD_DIR)/kernel.bin: always
+	$(ASM) $(SRC_DIR)/kernel/main.asm -f bin -o $(BUILD_DIR)/kernel.bin
+
+#
+# Always
+#
+always:
+	mkdir -p $(BUILD_DIR)
+
+#
+# Clean
+#
+clean:
+	rm -rf $(BUILD_DIR)/*

src/bootloader/boot.asm

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+	org 0x7c00
+	bits 16
+
+%define ENDL 0x0d, 0x0a
+
+;; FAT12 header start
+	jmp short start
+	nop
+
+bdb_oem:			db 'MSWIN4.1'		;8 bytes
+bdb_bytes_per_sector:		dw 512
+bdb_sectors_per_cluster:	db 1
+bdb_reserved_sctors:		dw 1
+bdb_fat_count:			db 2
+bdb_dir_entries_count:		dw 0E0h
+bdb_total_sectors:		dw 2880			; 2880 * 512 = 1.44MB
+bdb_media_descriptor_type:	db 0F0h			; F0 = 3.5" floppy
+bdb_sectors_per_fat:		dw 9			; 9 sectors/FAT
+bdb_sectors_per_track:		dw 18
+bdb_heads:			dw 2
+bdb_hidden_sector_count:	dd 0
+bdb_large_sector_count:		dd 0
+
+;; Extended boot record
+ebr_drive_number:		db 0 			; 0x00 = floppy, 0x80 hdd
+				db 0 			; reserved byte
+ebr_signature:			db 29h			; magic number?
+ebr_volume_id:			db 69h, 69h, 69h, 69h	; serial number
+ebr_volume_label:		db 'WEESLOS    '	; must be 11 bytes, pad with spaces
+ebr_system_id:			db 'FAT12   '		; must be 8 bytes, pad with spaces
+	
+;; FAT12 header end
+
+start:	
+	jmp main
+	
+;; Prints a string to the screen.
+;; Params:
+;; 	- ds;si points to string
+;; 
+puts:
+	;; push crap to stack that can/will be modified
+	push si
+	push ax
+	push bx
+.loop:
+	lodsb 		; loads next character into al
+	or al, al 	; verify if next character is null
+	jz .done 	; conditonal jump ifeq zero (if result of OR instruction above is zero)
+
+	mov ah, 0x0e 	; 0x0e "Teletype Output" subfunction of BIOS interrupt 0x10
+	mov bh, 0 	; set page number to 0
+	int 0x10 	; Call BIOS interrupt
+	
+	jmp .loop
+.done:
+	;; retrieve crap and return
+	pop bx
+	pop ax
+	pop si
+	ret
+	
+	
+main:
+	;;  Data segment setup
+	mov ax, 0 ; canot write to ds/es directly
+	mov ds, ax
+	mov es, ax
+
+	;; Stack initalization
+	mov ss, ax
+	mov sp, 0x7c00 ; stack will grow downwards in memory as it is filled
+
+	;;  print message
+	mov si, msg_hello
+	call puts
+	
+	hlt ; stop executing
+
+.halt:
+	jmp .halt ; really make sure we're not executing random shit
+	
+msg_hello: db 'Hello Shitass!', ENDL, 0	; named constant
+
+times 510-($-$$) db 0 	; pad program with zeros up to byte 510
+dw 0AA55h 		; BIOS requires last two bytes of first sector to be AA55

src/kernel/main.asm

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+	org 0x7c00
+	bits 16
+
+%define ENDL 0x0d, 0x0a
+
+start:	
+	jmp main
+	
+;; Prints a string to the screen.
+;; Params:
+;; 	- ds;si points to string
+;; 
+puts:
+	;; push crap to stack that can/will be modified
+	push si
+	push ax
+	push bx
+.loop:
+	lodsb 		; loads next character into al
+	or al, al 	; verify if next character is null
+	jz .done 	; conditonal jump ifeq zero (if result of OR instruction above is zero)
+
+	mov ah, 0x0e 	; 0x0e "Teletype Output" subfunction of BIOS interrupt 0x10
+	mov bh, 0 	; set page number to 0
+	int 0x10 	; Call BIOS interrupt
+	
+	jmp .loop
+.done:
+	;; retrieve crap and return
+	pop bx
+	pop ax
+	pop si
+	ret
+	
+	
+main:
+	;;  Data segment setup
+	mov ax, 0 ; canot write to ds/es directly
+	mov ds, ax
+	mov es, ax
+
+	;; Stack initalization
+	mov ss, ax
+	mov sp, 0x7c00 ; stack will grow downwards in memory as it is filled
+
+	;;  print message
+	mov si, msg_hello
+	call puts
+	
+	hlt ; stop executing
+
+.halt:
+	jmp .halt ; really make sure we're not executing random shit
+	
+msg_hello: db 'Hello Shitass!', ENDL, 0	; named constant
+
+times 510-($-$$) db 0 	; pad program with zeros up to byte 510
+dw 0AA55h 		; BIOS requires last two bytes of first sector to be AA55