base:turbotape_loader_source
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
.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
base/turbotape_loader_source.txt · Last modified: 2015-04-17 04:34 by 127.0.0.1