add kernel

src/kernel.asm

@@ -0,0 +1,62 @@
+; vim: ft=nasm
+org 0x7C00
+bits 16
+
+%define ENDL 0x0D, 0x0A
+
+start:
+	jmp main
+
+; 
+; echo:
+; print something to the screen
+;  - ds:si points to string
+;
+echo:
+	; save the registers we want to modify
+	push si
+	push ax
+	push bx
+
+	mov ah, 0xe
+	mov bh, 0
+
+.loop:
+	lodsb			; load byte from ds:si to al
+	or al, al		; check if next char is null
+	jz .done
+
+	int 0x10
+	jmp .loop
+
+.done:
+	pop bx
+	pop ax
+	pop si
+	ret
+
+main:
+
+	; setup data segments
+	; use ax as and intermediary as we can't write to es/ds directly
+	mov ax, 0
+	mov ds, ax
+	mov es, ax
+
+	; setup stack
+	mov ss, ax
+	mov sp, 0x7C00	; stack grows downward from where we are loaded in memory
+
+	; print the hello world
+	mov si, msg_hello
+	call echo
+
+	hlt
+
+.halt:
+	jmp .halt
+
+msg_hello: db 'Hello, world!', ENDL, 0
+
+times 510-($-$$) db 0
+dw 0AA55h