X-Git-Url: https://eleni.mutantstargoat.com/git/?p=bootboot;a=blobdiff_plain;f=bb.asm;h=a3f6011d3c0278dd8ebcb6b8f33315e33a140583;hp=fee43e4a37922f50ac73891a975e64c84d611610;hb=d715cdcc771d80ed4c39296a7ddc415331e3d342;hpb=21a64092fc52ade14e667feb3007a0276e30e24b

diff --git a/bb.asm b/bb.asm
index fee43e4..a3f6011 100644
--- a/bb.asm
+++ b/bb.asm
@@ -37,17 +37,6 @@ start:
 	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
@@ -96,7 +85,7 @@ 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
@@ -104,7 +93,90 @@ 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
+
+; 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
+
 .inf_loop:
 	jmp .inf_loop
+
+; random number generator
+; by nuclear
+rand:
+	mov eax, [randval]
+	mul dword [randmul]
+	add eax, 12345
+	and eax, 0x7fffffff
+	mov [randval], eax
+	shr eax, 16
+	ret
+
+randmul dd 1103515245
+randval dd 0ace1h