====== Turbo-tape Loader source ======

Depending on the selected options, this is the absolute minimum that is required to load Turbo-tape data. Sources are in XA assembler format. This assembles right out of the box to stack $0100.
Use SYS 256 or SYS 2^8 to launch the program. :) Uncomment DEFINEs for the different options. Enjoy!

Enthusi 11/2010

<code>
.word $0100

  zp1		=$c3
  zp2		=$c4
  BITCOUNT	=$02
  bytebuffer	=$bd
  zp3		=$c1
  zp4		=$c2
  chkbyte=$10
;---------------------------------
  *=$0100;
#define FX 1
#define CHKSUM 1
#define BASICRUN 1
#define MESSAGES 1
#define RESETMODE 1

  sei
begin

loader
init
#ifdef MESSAGES
  jsr $f817 ; print PRESS PLAY ON TAPE message
  ldy #00   ; Y is wasted then
#endif
  lda #$1d
  sta $01     ;  motor on
  ror $d011   ; screen blanked to d020
#ifdef CHKSUM
#ifndef RESETMODE
  sty chkbyte ;chose one that's 0 already per default? chkbyte=$10 is 0 after RESET
#endif
#endif
  sty $dd05 ;Y still 0
  lda #$fe  ; timer threshold for TurboTape
  sta $dd04
  jsr	sync	;-> x=0
  stx 	zp3	; instead of a later lda, sta
  jsr	get_byte	; important trick! Save time/bytes by using y-indexing
  tay	
initzp
  jsr	get_byte	
  sta	zp4,x	;X still 0
  inx
  cpx #$03
  bne initzp
debug
  jsr sync	;x=0
  ;----------------------------------------
  ;essential code from here on
e_start
load
  jsr	get_byte	
load1
  dec $01   ;to load below i/o area!
  sta	(zp3),y	
#ifdef CHKSUM
  eor chkbyte
  sta chkbyte
#endif
  inc $01
  iny	
  bne	next	
  inc	zp4	
next
  cpy	zp1
  lda	zp4	
  sbc	zp2	
  bcc	load	
#ifdef CHKSUM
  jsr get_byte
  cmp chkbyte
  beq ok
    inc $d020 ; color cycling in case of checksum error
    bvc *-3
#endif
ok
  rol $d011 ;screen back on
  lda 	#$37  ;default setting
  sta 	$01
#ifdef BASICRUN
  jsr $e453 ; prepare BASIC pointers for RUN 
  jsr $a660 ;
  jsr $a68e ; RUN
  jmp $a7ae ;
#else
  jmp $080d ;exomizer, or just launch the loaded code directly
#endif
;---------------------------------
get_byte
  lda	#$01	
  sta	bytebuffer	;init the to-be-read byte with 1
next_bit
  jsr	get_bit	
  rol	bytebuffer	
  bcc	next_bit	;is the initial 1 shiftet into carry already?
  lda	bytebuffer	; much nicer than ldx #8: dex: loop
  rts	
;---------------------------------
get_bit
  lda	#$10	
bit_loop
  bit	$dc0d	
  beq	bit_loop	;busy loop to detect signal
  lda	$dd0d	
  pha	
  lda	#$19	
  sta	$dd0e	
  pla
#ifdef FX
  sta $d020 ;use bitvalue as d020 effect (I love that one)
#endif
  lsr	
  rts	

e_end
;---------------------------------
sync
  jsr get_bit 
  rol bytebuffer  
  lda bytebuffer  
  cmp #$02  
  bne sync
  ldx #$09  ;9,8,... is real turboTape
sync2       ;I sometimes used 8,7,6... to avoid it being listed in vice :)
  jsr get_byte
  cmp #$02
  beq sync2
sync3 
  cpx bytebuffer
  bne sync
  jsr get_byte  
  dex
  bne sync3 
  rts 
</code>