X-Git-Url: https://eleni.mutantstargoat.com/git/?p=bootboot;a=blobdiff_plain;f=bb.asm;h=3f4bcd1debf141a33485c37ef5e29a87cbe43f50;hp=b3ef81449ef72144012424a165001b4e7252597c;hb=6c37e30642cc79c97c8e563f21ea6002fa41d0b2;hpb=27427fd7f284b5359def788acbccff31989cdecf

diff --git a/bb.asm b/bb.asm
index b3ef814..3f4bcd1 100644
--- 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
@@ -79,7 +96,7 @@ clearscreen:
 	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
@@ -87,7 +104,44 @@ saved_drive_num:
 	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
+
+; 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
+
 .inf_loop:
 	jmp .inf_loop