mov es, ax
mov ss, ax
-; save dx value
+; save dl value
+; bios sets in dl the num of the drive that
+; loaded you so if you overwrite dl you can reuse it
mov [saved_drive_num], dl
; service 0: set videomode ah
; param: which video mode (13h: 320x200, 256 colors) al
; ax: ah (high 8 bits), al (low)
+; call 0 = set_videomode it expects the video mode in al
+; ah : 0, al: 13, ax:ahal
mov ax, 13h
; calling video bios
; software interrupt 10h
+; what's the value of ah? al=video mode when ah=0
+; which set which video mode
int 10h
mov ax, 3
call clearscreen
+; waiting for keypress
+; x86 has 2 special instructions to read/write from I/O
+; devices: in and out (because some processors have different
+; address spaces for devices and for memory, arm not)
+.key_wait:
+ in al, 64h ; 60h = keyb data port, 64h = keyb status port
+ and al, 1 ; 1 = OUTBUF_FULL = the keyb controller out buf is full
+ jz .key_wait
+
+ in al, 60h ; reads the keyb that was pressed to reset the flag
+
; load 2nd sector from boot device and jump to it
; bios helpers, 13h = disk io
mov ax, 0
ret
saved_drive_num:
- db 0 ; declare byte 0
+ db 0 ; define byte 0
; assembler trick: write as many 0 needed to fill 510 bytes
; $ <- means here
dw 0aa55h
sector_2:
- mov ax, 5
- call clearscreen
+; disp palette
+ mov ax, 0a000h ; video segment points to video memory
+ mov ds, ax
+ mov bx, 0 ; video offset
+ mov cx, 0 ; y
+.y_loop:
+ mov dx, 0 ; x
+.x_loop:
+ mov ax, dx
+ test ax, 0ff00h ; lower 8 bits 0, highest 1, Z flag is set while < 256, test = and but doesnt change ax
+ jz .skip_clear_ax
+ mov al, 0
+.skip_clear_ax:
+ mov [bx], al ; pixel written on screen
+ inc bx ; increment
+ inc dx
+ cmp dx, 320
+ jnz .x_loop
+ inc cx
+ cmp cx, 200
+ jnz .y_loop
+
+; fix palette (256 colors)
+
.inf_loop:
jmp .inf_loop