From b2610491c7502aa2c0f26bdf8128c57d934df92a Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Sat, 28 Jan 2017 23:31:26 +0100
Subject: [PATCH] Hello world in a mbr

---
 Readme.md |  8 ++++++
 mbr.asm   | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/Readme.md b/Readme.md
index 57ae4ec..60e0a5e 100644
--- a/Readme.md
+++ b/Readme.md
@@ -6,6 +6,14 @@ Build with
 Run with
  qemu-system-x86_64 -boot a -fda  mbr
 
+Debug with
+ qemu-system-x86_64 -boot a -fda  mbr -s -S
+ gdb
+  target remote localhost:1234
+  layout asm
+  b *0x7c00
+  c
+
 == Bios Memory ==
 
 0x0     -   0x03FF      ;IVT
diff --git a/mbr.asm b/mbr.asm
index 3103f0d..5a47387 100644
--- a/mbr.asm
+++ b/mbr.asm
@@ -1,7 +1,74 @@
 bits 16				; mode 16bits
 org 0x7C00			; mbr ae loaded at 0x7C00
-mov al, 41h         ; put 'A' in al
-mov ah, 0eh         ; we want to call function 09h (Write Character and Attribute at Cursor) from interupt 10h
-int 10h
+
+jmp boot
+
+display_enable:
+    push bp
+    mov bp, sp
+    mov ah, 0h      ; 00h    Set Video Mode
+    mov al, 07h     ; Txt, monochrome, 80x25
+
+    int 10h
+
+    mov sp, bp
+    pop bp
+    ret
+
+print:
+    push bp
+    mov bp, sp
+    mov si, [bp + 4]; put first function arg in si. sp is stask pointer
+.loop:
+    lodsb           ; load si content into al then inc si
+    cmp al, 0;
+    je .end
+
+    mov ah, 0eh
+    mov bx, 0
+    int 10h
+
+    jmp .loop
+
+.end:
+    mov sp, bp
+    pop bp
+    ret
+
+println:
+    push bp
+    mov bp, sp
+    push word [bp + 4]
+    call print
+    add sp, 2
+
+    mov ah, 03h     ; read cursor position
+    int 10h         ; row number in dh. Col in dl
+
+    inc dh          ; goto next line
+    mov dl, 0
+
+    mov ah, 02h     ; Set Cursor Position
+    int 10h
+    mov sp, bp
+    pop bp
+    ret
+
+hello db 'Hello world', 0
+name db 'This is a name', 0
+
+boot:
+    sti             ; enable virtual interupts
+
+    call display_enable
+
+    push hello
+    call println
+    add sp, 2
+
+    push name
+    call println
+    add sp, 2
+
 times 510 - ($ - $$) db 0	; fill up to 510 with 0
 dw 0xAA55			; MBR magic number