From: Duje Mihanović <duje.mihanovic@skole.hr>
Date: Fri, 20 Aug 2021 14:46:08 +0000 (+0200)
Subject: Add basic bootsector
X-Git-Tag: 0.1.0~31
X-Git-Url: http://git.dujemihanovic.xyz/%22http:/www.sics.se/static/%7B%7B%20%24image.RelPermalink%20%7D%7D?a=commitdiff_plain;h=4326df7844154f8c575a33b3898709944e08f74b;p=nameless-os.git

Add basic bootsector

It prints out "Gotta start somewhere". Tested on QEMU and even on real hardware
with success.
---

4326df7844154f8c575a33b3898709944e08f74b
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..12ab2c1
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+toolchain/
+boot
diff --git a/boot.s b/boot.s
new file mode 100644
index 0000000..50730d0
--- /dev/null
+++ b/boot.s
@@ -0,0 +1,22 @@
+	bits 16 ; boot sectors run in real mode
+	org 7c00h ; boot sector is always loaded at 0x7c00
+
+	mov al, 1 ; update cursor after write
+	mov bh, 0 ; write to page 0
+	mov bl, 00000111b ; attribute: high nibble is foreground (light gray),
+					  ; low nibble is background (black)
+					  ; NOTE: in the binary, these will be inverted, so low nibble here will become high nibble in binary and vice versa!
+	mov cx, msg1end - msg1 ; size of message
+	mov dl, 0 ; column to write to
+	mov dh, 0 ; row to write to
+	push cs ; push code segment to stack
+	pop es ; pop pushed code segment to extra segment, this serves as the base to the string
+	mov bp, msg1 ; offset where the string is
+	mov ah, 13h ; write string subservice 
+	int 10h ; call BIOS interrupt 0x10
+	jmp msg1end ; jmp to endless loop
+	msg1 db "Gotta start somewhere"
+	msg1end: jmp msg1end
+
+	times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached
+	dw 0xaa55 ; BIOS MBR signature