+; setup grayscale palette (64 first colors because ramdac uses 6 bits / color so 2^6)
+; ram dac (digital to analog converter) tis vga
+; in a ^ register which index we want to write
+; 3 writes in another ramdac register (data)
+; ramdac feature: when you need to set a palette
+ mov al, 0 ; first index
+ mov dx, 3c8h ; ramdac index registe
+ out dx, al ; because io port (address) > 255
+ inc dx ; ramdac data register: 3c9h
+.pal_loop:
+ out dx, al ; r
+ out dx, al ; g
+ out dx, al ; b
+ inc al
+ test al, 3fh ; test with 3fh to keep the lowest 6 bits of al
+ jnz .pal_loop
+
+; disable all interrupts (for bios to not read the keyboard)
+ cli
+
+ ; ds on 0 because rand uses it for accesses to mem
+ xor ax, ax
+ mov ds, ax
+ mov ax, 0a000h
+ mov es, ax
+main_loop:
+; wait for vblank
+ mov dx, 3dah
+ in al, dx
+ and al, 8 ; the 4th bit is 1 when we are in the vertical blanking period
+ jz main_loop
+
+ xor bx, bx ; mov bx, 0 to clear the register
+.static_loop:
+ call rand
+ and ax, 3fh ; last six bits of eax (see rand)
+ mov [es:bx], al ; [] -> bx offset and default segment ds we change it to es
+ inc bx
+ cmp bx, 64000 ; num pixels
+ jnz .static_loop
+
+ 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 main_loop ; no key pressed, loop back
+ in al, 60h ; reads the keyb that was pressed to reset the flag
+
+; re-enable all interrupts
+ sti
+