extract game from bootloader

bootloader.asm

@@ -0,0 +1,41 @@
+; initialize the environment
+mov ax, 0x07c0
+mov ds, ax
+
+; the segment of the game
+mov ax, 0x07e0
+
+; setup the file-source
+mov ch, 0x00    ; cylinder 0
+mov cl, 0x02    ; sector 2 (skip first sector, which is the bootloader)
+mov dh, 0x00    ; head 0
+mov dl, 0x00    ; drive 0 (floppy disk)
+
+; setup the destination
+mov es, ax      ; segment starts directly after the bootloader (7c00 - 7dff)
+mov bx, 0x0000
+
+; copy data into RAM
+read:
+  mov al, 0x02    ; read two sectors
+  mov ah, 0x02    ; int 13h subfunction 2 -> read sectors (512 bytes) from disk
+  int 0x13        ; copy sectors to ES:BX
+  jc read         ; carry-flag is set -> there was a read-error, retry
+
+; rebase segments for game execution
+mov ax, 0x07e0
+mov ds, ax  ; data segment
+mov es, ax  ; additional segments
+mov fs, ax
+mov gs, ax
+mov ss, ax  ; stack segment
+
+; reset stack pointer
+; mov sp, 0x0000
+
+; enter the game code -> set CS:IP
+jmp 0x07e0:0x0000
+
+; spacing and signature
+times 510 - ($ - $$) db 0
+dw 0xaa55

scripts/create.sh

@@ -0,0 +1,5 @@
+nasm bootloader.asm -f bin -o build/bootloader.bin
+nasm space-invaders.asm -f bin -o build/space-invaders.bin
+
+dd if=build/bootloader.bin of=build/image.bin bs=512 count=1
+dd if=build/space-invaders.bin of=build/image.bin bs=512 count=2 seek=1

scripts/start.sh

@@ -0,0 +1 @@
+qemu-system-x86_64 -fda build/image.bin

si.asm → space-invaders.asm

@@ -1,11 +1,7 @@
-; initialize the environment
-mov ax, 0x07c0
-mov ds, ax      ; set the DS to the start of the programm
-                ; this has to be indirectly, since all segement-registers can not directly be written to.
-
+; clear the cursor blinking
 mov	ah, 0x01
 mov	cx, 0x2000
-int 	0x10  ; clear the cursor blinking
+int 	0x10
 
 ; calculate game screen position
 mov	ah, 0x0F
@@ -18,7 +14,6 @@ mov [displayOffset], ah
 ; initialize the bullet list by setting  the end-pointer to the list-start
 mov word [bulletListEnd], bulletListStart
 
-
 ; game logic
 gameLoop:
   call clearScreen
@@ -324,6 +319,5 @@ bulletListStart db 0x00
 
 
 ; ################################################
-; spacing and signature
-times 510 - ($ - $$) db 0
-dw 0xaa55
+; spacing
+times 1014 - ($ - $$) db 0