; bitfield.a48
; Version 1.1
;
; History:
; Version 1.1
;   Removed unnecessary call vdcenable at beginning.
;
; Version 1.0
;   first release
;
; This program shows how to use the bitfield routines, how to wait for
; pressed keys on the keyboard and how to use VSYNC and line interrupts.
; You can change single bits in the horizontal grid. Use "+" to edit
; next bit, "-" to edit previous bit, "1" to set bit, "0" to clear bit.

; Copyright (C) 1997-1999 by Soeren Gust, sgust@ithh.informationstheater.de

; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, write to the Free Software
; Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

; You can always get the latest version at http://soeren.informationstheater.de

	cpu	8048

; variables in internal ram

iram_work	equ	020h
iram_value	equ	021h
iram_ictrl	equ	022h	; control irq
iram_vdcctrl	equ	023h	; control value from VDC

ictrl_blink	equ	080h	; if set, do the blinking
ictrl_lineirq	equ	040h	; if set, do the lineirq

	org	400h
	
	include	"g7000.h"

	jmp	selectgame	; RESET
	jmp	irq		; interrupt
	jmp	timeirq		; timer
	jmp	myvsyncirq	; VSYNC-interrupt
	jmp	start		; after selectgame
	jmp	soundirq	; sound-interrupt

start
	call	gfxoff

	; initialise variables
	mov	a,#025h		; the bit in the middle
	mov	r0,#iram_work
	mov	@r0,a
	mov	a,#1		; middle bit is set
	mov	r0,#iram_value
	mov	@r0,a
	mov	r0,#iram_ictrl
	mov	a,#0		; don't blink yet
	mov	@r0,a

	; set grid
	mov	r0,#vdc_gridh0
	mov	r1,#gridh & 0ffh
	mov	r2,#9
loopgh
	mov	a,r1		; source
	movp	a,@a		; get value
	movx	@r0,a		; store in vdc
	inc	r0
	inc	r1
	djnz	r2,loopgh

	call	gfxon

	; activate blinking and line irq
	mov	r0,#iram_ictrl
	mov	a,#ictrl_blink | ictrl_lineirq
	mov	@r0,a

main	; begin of main loop
	call	waitforkey	; let user press a key
	mov	r7,a		; store it for later

	mov	r0,#iram_work
	mov	a,@r0		; get active bit
	mov	r6,a		; new bit, if any
	mov	r5,a		; old bit

	mov	a,r7
	xrl	a,#010h		; "+" key
	jnz	noplus
	inc	r6
noplus
	mov	a,r7
	xrl	a,#028h		; "-" key
	jnz	nominus
	dec	r6
nominus

	; test, if bit changed
	mov	a,r5
	xrl	a,r6
	jz	nonewbit	; not changed

	; the user wants a new bit
	; we play with the same registers as out irq
	; so disable irq while changing bits
	; we need access to VDC, gfxoff re-enables irq
	; so turn gfx off before the irq
	call	gfxoff
	dis	i
	; set new bit active, r0==iram_work
	mov	a,r6
	mov	@r0,a
	; set old bit to value
	mov	r1,#vdc_gridh8+1
	mov	r0,#iram_value
	mov	a,@r0
	jnz	setoldbit
	mov	a,r5
	call	bitclear
	jmp	nooldbit
setoldbit
	mov	a,r5
	call	bitset
nooldbit

	; set value to new bit
	mov	r1,#vdc_gridh8+1
	mov	a,r6
	call	bittest
	mov	r0,#iram_value
	mov	@r0,a

	en	i
	call	gfxon		; outside of dis/en i
nonewbit

	; now test for "0" and "1"
	; the key which is pressed is still in r7
	mov	r0,#iram_value
	mov	a,r7
	xrl	a,#0		; "0"
	jnz	nozero
	mov	@r0,a		; a == 0, because jnz
nozero

	mov	a,r7
	xrl	a,#1		; "1"
	jnz	noone
	cpl	a		; a == 0, because jnz
	mov	@r0,a
noone

	jmp	main

	; the default grid

gridh:	db	001h, 082h, 044h, 028h, 010h, 028h, 044h, 082h, 001h

	; my own vsync irq routine
	; it starts the lineirq and does the blinking
myvsyncirq
	; start lineirq, if needed
	mov	r0,#iram_ictrl	; control register
	mov	a,@r0
	cpl	a
	jb6	myvsyncnoline	; should we start line irq ?
	mov	a,@r0
	mov	a,#088h		; middle of the screen
	mov	t,a		; set # of lines to wait
	strt	cnt		; start line counting
	en	tcnti		; enable timer irq
myvsyncnoline

	; set grid+background color
	mov	r0,#vdc_color
	mov	a,#col_grd_white | col_grd_lum
	movx	@r0,a

	; do the blinking
	mov	r0,#iram_ictrl	; control register
	mov	a,@r0
	jb7	myvsynccont	; should we blink ?
	jmp	vsyncirq	; thats all for now

myvsynccont
	mov	a,@r0		; count the frames
	inc	a
	mov	@r0,a

	anl	a,#03fh		; mask out framecounter
	xrl	a,#00ah		; wait more frames ?
	jz	myvsyncblink
	jmp	vsyncirq	; thats all for now

myvsyncblink
	mov	a,@r0
	anl	a,#0c0h		; restart frame counter
	mov	@r0,a

	; turn grid gfx off, the bios-routine is not safe
	; to use in irq, it leaves with RB1 and EN I
	mov	r1,#iram_vdcctrl
	mov	r0,#vdc_control
	movx	a,@r0
	mov	@r1,a		; store old vdc_control
	anl	a,#0f6h
	movx	@r0,a

	mov	r0,#iram_work	; get the bit to blink

	mov	r1,#vdc_gridh8+1
	mov	a,@r0
	call	bittest		; test bit to blink
	movx	a,@r1		; invert the bit we have
	xrl	a,r2
	movx	@r1,a

	; restore old VDC status
	mov	r1,#iram_vdcctrl
	mov	r0,#vdc_control
	mov	a,@r1
	movx	@r0,a

	jmp	vsyncirq	; continue vsyncirq

timeirq:
	sel	rb0
	mov	r5,a
	stop	tcnt

	in	a,P1
	mov	r6,a
	call	vdcenable

	; set grid+background color
	mov	r0,#vdc_color
	mov	a,#col_grd_yellow | col_grd_lum | col_bck_blue

	; wait until end of current scan line to avoid changing
	; the background in the middle of the screen
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	movx	@r0,a

	mov	a,r6
	outl	P1,a

	mov	a,r5
	retr

	end