initial import of turbo tape routine

c64/kernal/tape/load_tape_turbo.s

@@ -3,12 +3,157 @@
 // Tape (turbo) part of the LOAD routine
 //
 
+// Based on routine by enthusi/Onslaught, found here:
+// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
+
 
 #if CONFIG_TAPE_TURBO
 
 
+
+
+tape_ask_play:
+
+	sei                                // timing is critical for tape loading
+
+	lda #$1D
+	sta CPU_R6510                      // motor on   XXX make it more system friendly
+
+	ror VIC_SCROLY                     // screen blanked to VIC_EXTCOL color   XXX make it more system friendly
+
+	// XXX finish the implementation
+
+	rts
+
+tape_load_success:
+
+	rol VIC_SCROLY // screen back on
+	lda #$37       // default setting
+	sta CPU_R6510
+
+	// XXX finish this routine
+
+	rts
+
+tape_load_error:
+
+	// XXX finish this routine
+
+	rts
+
+
 load_tape_turbo:
-	STUB_IMPLEMENTATION()
+
+	// XXX if VERIFY asked - error
+
+	ldy #$00
+	sty PRTY                           // initial checksum value
+
+	jsr tape_ask_play
+
+	sty CIA2_TIMAHI                    // .Y still 0
+	lda #$FE                           // timer threshold for TurboTape
+	sta CIA2_TIMALO
+
+	// Read file header
+
+	jsr tape_turbo_sync                // .X gets set to 0
+
+	stx STAL+0                         // instead of a later lda, sta
+	jsr tape_turbo_get_byte            // important trick - save time/bytes by using y-indexing
+	tay
+!:
+	jsr tape_turbo_get_byte	
+	sta STAL+1,x                       // .X still 0
+	inx
+	cpx #$03
+	bne !-
+
+	// Read file payload
+
+	jsr tape_turbo_sync                // .X gets set to 0
+
+	// FALLTROUGH
+
+load_tape_turbo_loop:
+
+	jsr tape_turbo_get_byte
+
+	dec CPU_R6510                      // to load below i/o area!
+
+	sta (STAL),y	
+	eor PRTY
+	sta PRTY
+
+	inc CPU_R6510
+
+	iny
+	bne !+
+	inc STAL+1
+!:
+	cpy MEMUSS+0
+	lda STAL+1
+	sbc MEMUSS+1
+	bcc load_tape_turbo_loop
+
+	// Verify the checksum
+
+	jsr tape_turbo_get_byte
+	cmp PRTY
+	beq_far tape_load_success
+	jmp tape_load_error
 
 
-#endif
+tape_turbo_get_byte:
+
+	lda #$01	
+	sta ROPRTY                         // init the to-be-read byte with 1
+!:
+	jsr tape_turbo_get_bit	
+	rol ROPRTY
+	bcc !-	                           // is the initial 1 shifted into carry already?
+	lda ROPRTY                         // much nicer than ldx #8: dex: loop
+	
+	rts	
+
+
+tape_turbo_get_bit:
+
+	lda #$10	
+!:
+	bit CIA2_ICR	
+	beq !-                             // busy loop to detect signal
+	lda CIA2_ICR
+	pha	
+	lda #$19	
+	sta CIA2_CRA	
+	pla
+	sta VIC_EXTCOL                     // use bitvalue as d020 effect (I love that one)
+	lsr
+
+	rts
+
+
+tape_turbo_sync:
+
+	jsr tape_turbo_get_bit 
+	rol ROPRTY  
+	lda ROPRTY  
+	cmp #$02  
+	bne tape_turbo_sync
+	ldx #$09                           // 9,8,... is real turboTape
+!:                                     // I sometimes used 8,7,6... to avoid it being listed in vice :)
+ 	jsr tape_turbo_get_byte
+ 	cmp #$02
+ 	beq !-
+!: 
+	cpx ROPRTY
+	bne tape_turbo_sync
+	jsr tape_turbo_get_byte  
+	dex
+	bne !-
+
+	rts 
+
+
+#endif // CONFIG_TAPE_TURBO