diff options
| -rw-r--r-- | bsect.s | 92 |
1 files changed, 92 insertions, 0 deletions
@@ -0,0 +1,92 @@ +org 0x7C00 + +init: + mov word [body_start], 2000 + mov word [body_end], 2000 + mov word [head_dir], -160 + ; clear the screen + mov ax, 0xB800 + mov es, ax + mov cx, (80 * 25) + xor ax, ax + mov di, ax + rep stosw + ; clear the game memory + mov es, ax + mov di, 0x0500 + mov cx, (80 * 25) + rep stosw + + call game_tick + + ; store the original timer isr + cli + xor ax, ax + mov ax, [32] + mov [orig_isr8], ax + mov ax, [34] + mov [orig_isr8 + 2], ax + ; install our timer isr + mov word [32], timer_tick + mov word [34], 0 + sti + +.loop: + jmp .loop + +orig_isr8: dd 0 +tick_count: db 0 +timer_tick: + mov al, [tick_count] + inc al + cmp al, 9 + jl .nogametick + call game_tick +.nogametick: + mov [tick_count], al + jmp far [orig_isr8] + +game_tick: + ; grab some vars before switching to game seg + mov si, [body_start] + mov di, [body_end] + mov dx, [head_dir] + mov ax, 0x0050 + mov ds, ax + mov es, ax + +.noinit: + ; update head position + mov ax, si + add ax, dx + mov [si], ax + mov si, ax + mov bx, [di] + mov word [di], 0 + mov di, bx + + ; check if body overlapping + cmp word [si], 0 + je .nodie + add sp, 2 + jmp init +.nodie: + +.end: + xor ax, ax + mov ds, ax + mov es, ax + mov [body_start], si + mov [body_end], di + ret + +head_dir: dw 0 +body_start: dw 0 +body_end: dw 0 + +; Pad out the rest of the boot sector and add magic bytes +times 510 - ($ - $$) db 0 +dw 0xAA55 + +; Pad out the rest of a 1.44MB floppy image +times (2880 * 512) - ($ - $$) db 0 |