X-Git-Url: https://eleni.mutantstargoat.com/git/?p=bootboot;a=blobdiff_plain;f=bb.asm;h=a3f6011d3c0278dd8ebcb6b8f33315e33a140583;hp=f5c84afc9c6306c395f5b90eea68e229f2f29fd9;hb=d715cdcc771d80ed4c39296a7ddc415331e3d342;hpb=6e624974ddfa6a1b7a195dd20800c469347579e1

diff --git a/bb.asm b/bb.asm
index f5c84af..a3f6011 100644
--- a/bb.asm
+++ b/bb.asm
@@ -11,19 +11,49 @@
 start:
 	mov sp, 7c00h
 
+; initialize segment registers
+	mov ax, 0
+	mov ds, ax
+	mov es, ax
+	mov ss, ax
+
+; 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
 
-; infinite loop
-end:
-	jmp end
+; load 2nd sector from boot device and jump to it
+; bios helpers, 13h = disk io
+	mov ax, 0
+	mov ds, ax
+	mov ah, 02h 			; call 2: read sectors into memory
+	mov al, 1				; number of sectors to read
+	mov ch, 0				; low 8 bits of cylinder number
+	mov cl, 2				; sector number that starts from 1
+	mov dh, 0				; head number
+	mov dl, [saved_drive_num]	; 8bits
+	mov bx, sector_2
+	int 13h
+; error check: if carry flag isn't set jump to loaded code
+	jnc	sector_2
+.inf_loop:
+	jmp .inf_loop
+
 
 clearscreen:
 ; video ram is mapped in a0000
@@ -37,12 +67,14 @@ clearscreen:
 ; automatically set to 7c0 (7c00h)
 ; offset can be paired with any register
 ; pair the registers
+	push ax
 	mov ax, 0a000h
 	mov ds, ax
 	mov di, 0
+	pop ax
 ; counter cx
 	mov cx, 64000
-	mov ax, 3
+
 .loop_begin:
 ; dereferrence[] address
 	mov [di], al
@@ -52,7 +84,99 @@ clearscreen:
 	jnz .loop_begin
 	ret
 
+saved_drive_num:
+	db 0 ; define byte 0
+
 ; assembler trick: write as many 0 needed to fill 510 bytes
 ; $ <- means here
 	times 510-($-$$) db 0
 	dw 0aa55h
+
+sector_2:
+; 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