; === "EXPRESS TRAIN 125" BY PWP ===
;
; This is just a proof of concept.
; The main point here is that tiny MS-DOS demos with PCM sound are possible.
;
; Compiles with nasm.
;
; Uses COVOX sound, use Dosbox to emulate it.
;
; viznut/pwp 2011-11-05
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

	bits 16
	org 0x100

	mov al,0x13
	int 0x10
	push cs
	pop ds
	call hooktimer

	mov dword[melody],3
	mov dword[timctr],0
	mov word[beatsy],5
	mov dword[speedy],5

	;;; MAINLOOP

	push 0xa000
	pop es

l1:
	mov bx,[timctr+1]
	push 0xa200
	pop es
	add ax,cx
l0:
	add bx,cx 
	xor ax,bx
	and ax,bx
	push cx
	pop cx
	xor ax,cx
	xor ax,[timctr+1]
	and ax,15
	add ax,15
	xor ax,[melody]
	stosb
	loop l0

	; Tekstii pitäis olla
	push ax ; Jännäobminointeja ei ole
	push bx
	push cx
	push dx
	xor ax,ax
	xor bx,bx
        mov dh,0 ; Pystyrivi
	mov dl,5 ; Vaakarivi - ei tosin tee mitään
        mov bh,0 ; emt
        mov ah,2 ; emt
        int 10h ; emt
        mov dx,hello ; Hello, world siihen niin kivasti
        mov ah,9 ; funktio tekstirivin printtauksee
        int 21h ; interrupteri notta ko. funktio vedettäs

	pop dx
	pop cx
	pop bx
	pop ax

	cmp dword[timctr],16383
	jle changed
	mov dword[melody],5
	cmp dword[timctr],32766
	jle changed
	mov word[melody],7
	cmp dword[timctr],49150
	jle changed
	mov word[melody],3
	cmp dword[timctr],81919
	jle changed
	mov word[melody],2
	cmp dword[timctr],90110
	jle changed
	mov word[melody],1
	cmp dword[timctr],98301
	jle changed
	mov word[melody],2
	cmp dword[timctr],114684
	jle changed
	mov word[melody],4
	cmp dword[timctr],131067
	jle changed
	mov word[melody],3
	cmp dword[timctr],147451
	jle changed
	mov dword[timctr],0
	mov word [beatsy],4
	mov word [speedy],8
changed:

	in al,0x60	; esc key check
	cbw
	dec ax
	jnz l1

	;;; (UN)INIT CODE

	mov al,0x3
	int 0x10
	lds dx,[oldint]
	jno timset
hooktimer:
	mov ax,0x3508
	int 0x21
	push es
	push bx
	pop dword [oldint]
	mov dx,handler
	mov ah,0x99	; interrupt rate (0x20 is about 36 kHz i think)
timset:	mov al,0x36
	out 0x43,al
	mov al,ah
	out 0x40,al
	mov al,0
	out 0x40,al
	mov ax,0x2508
	int 0x21
	ret

	;;; TIMER IRQ HANDLER

handler:
	pusha

	mov ax,[timctr]
	mov dx,ax
	mov bx,dx

	imul dx,[melody]
	mov cl,[beatsy]
	shr bx,cl

	; (5) sit 4 ku alempi o 9
	or dx,bx
	
	shr ax,6
	or ax,dx

	mov bx,dx
	; (5)  sit 7
	; sit 9
	imul dx,[speedy]
	shr bx,2
	and dx,bx
	and ax,dx

	mov dx,0x378
	out dx,al

	inc dword [timctr]

	;cmp dword[timctr],1024
	;jne change
	
	mov al,0x20
	out 0x20,al
	
	popa
	iret


	;;; VARIABLES

hello db "Dignity: Separate, Rebuild.          Annihilate, Compile, Run$"
timctr equ $+0
oldint equ $+4
melody equ $+8
beatsy equ $+12
speedy equ $+16