step 3: wait for keypress

diff --git a/bb.asm b/bb.asm
index b3ef814..fee43e4 100644 (file)
--- a/bb.asm
+++ b/bb.asm
@@ -17,20 +17,37 @@ start:
        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