tape code cleanup, added impulse detection for normal mode

c64/kernal/tape/load_tape_normal.s

@@ -7,17 +7,19 @@
 // We have the following possible CPU frequencies:
 // - C64    PAL:  CPU frequency 0.985248 MHz
 // - C64    NTSC: CPU frequency 1.022727 MHz
-// - VIC-20 PAL:  CPU frequency 1.108405 MHz
+// Average is 1.0039875 MHz and we will take this value for calculation (but it really does not change much).
-// - VIC-20 NTSC: CPU frequency 1.022727 MHz
+//
-// Since VIC-20 tapes are not expected to be loaded often, routine will be optimized for C64 timings
-
 // We have to distinguish the following pulse lengths (http://sidpreservation.6581.org/tape-format/):
 // - S (short)    352 us
 // - M (medium)   512 us
 // - L (long)     672 us
-// This gives us the following thresholds (where average CPU frequency is 1.0039875 MHz):
+//
-// - S vs M       432 us (54 8-cycle periods)
+// This gives us the following thresholds
-// - M vs L       592 us (74 8-cycle periods)
+// - S vs M       432 us (108 or $6C 4-tick periods)
+// - M vs L       592 us (149 or $95 4-tick periods)
+//
+// 4-tick periods should be enough - TAP file format description (http://unusedino.de/ec64/technical/formats/tap.html)
+// tells it uses exactly 8 PAL ticks as a resolution
 
 // The following encoding is used:
 // (S,M) = 0 bit
@@ -30,7 +32,50 @@
 
 
 load_tape_normal:
-	STUB_IMPLEMENTATION()
+
+	jsr tape_ditch_verify              // only LOAD is supported, no VERIFY
+
+	// Setup CIA #2 timers
+	
+	ldx #$03                           // set timer A to 4 ticks
+	stx CIA2_TIMALO // $DD04
+	ldx #$00
+	stx CIA2_TIMAHI // $DD05
+
+	stx CIA2_TIMBHI // $DD07
+	dex                                // puts $FF - for running timer B as long as possible
+	stx CIA2_TIMBLO // $DD06
+
+	// Let timer A run continuously
+
+	ldx #%00010001                     // start timer, force latch reload
+	stx CIA2_CRA  // $DD0E
+
+	// Start playing
+
+	jsr tape_clean_sid
+	jsr tape_ask_play
+
+	// FALLTROUGH
+
+load_tape_normal_header:
+
+	// XXX replace this placeholder by a real routine
+
+
+	jsr tape_load_get_pulse
+	ldx #$00
+	cmp #($100 - $6C - $05)
+
+	bcs !+
+#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
+	ldx #$0B
+#else
+	ldx #$06
+#endif
+!:
+	stx VIC_EXTCOL
+	jmp load_tape_normal_header
 
 
 #endif

c64/kernal/tape/load_tape_turbo.s

@@ -98,88 +98,5 @@ load_tape_turbo_loop:
 	beq_far tape_load_success
 	jmp tape_load_error
 
-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 CIA1_ICR // $DC0D	
-	beq !-                             // busy loop to detect signal
-	lda CIA2_ICR // $DD0D
-	pha	
-	lda #$19	
-	sta CIA2_CRA // $DD0E	
-	pla
-	
-	pha                                // audio/video effects
-	asl
-	sta SID_SIGVOL
-	beq !+
-#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
-	lda #$0B
-#else
-	lda #$06
-#endif
-!:
-	sta VIC_EXTCOL
-	pla
-
-	lsr
-	rts
-
-tape_turbo_sync_common:
-
-	jsr tape_turbo_get_bit 
-	rol ROPRTY
-	lda ROPRTY
-	cmp #$02
-	bne tape_turbo_sync_common
-	rts
-
-tape_turbo_sync_header:
-
-	ldx #$FF
-!:
-	ldy #$03
-!:
-	jsr tape_turbo_sync_common
-	dey
-	bne !-
-	dex
-	bne !--
-
-	// FALLTROUGH
-
-tape_turbo_sync_payload:
-
-	jsr tape_turbo_sync_common
-!:
-	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 !-
- 	ldy #$00
-!: 
-	cpx ROPRTY
-	bne tape_turbo_sync_payload
-	jsr tape_turbo_get_byte
-	dex
-	bne !-
-
-	rts 
-
 
 #endif // CONFIG_TAPE_TURBO

c64/kernal/tape/tape_normal_get_pulse.s

@@ -0,0 +1,42 @@
+
+//
+// Tape (turbo) helper routine - pulse reading
+//
+// Returns pulse length (with a bias, see comments) in .A
+//
+
+
+#if CONFIG_TAPE_NORMAL
+
+
+tape_load_get_pulse:
+
+	// Contrary to original ROM implementation we do not use interrupts
+	// (see http://unusedino.de/ec64/technical/formats/tap.html) - busy wait
+	// implementation is probably just shorter
+
+	lda #$10
+!:
+	bit CIA1_ICR    // $DC0D
+	bne !-
+!:   
+	bit CIA1_ICR    // $DC0D
+	beq !-                             // busy loop to detect signal, restart timer afterwards
+	lda CIA2_TIMBLO // $DD06
+	ldx #%01010001                     // start timer, force latch reload, count timer A underflows
+	stx CIA2_CRB    // $DD0F
+
+	// Since the signal appeared to the point of timer restart we used:
+	// bit - 4 cycles
+	// beq - 2 cycles
+	// lda - 4 cycles
+	// ldx - 2 cycles
+	// stx - 4 cycles
+	// plus approx. 3 cycles (bit + beq time divided by 2) from value change to 'bit' instruction,
+	// this is total 19 cycles, or $5 periods of 4 ticks (timer A) each - we need to take it into account
+	// every time we check the pulse length
+
+	rts
+
+
+#endif

c64/kernal/tape/tape_turbo_get_bit.s

@@ -0,0 +1,42 @@
+
+//
+// Tape (turbo) helper routine - bit reading
+//
+
+// Based on routine by enthusi/Onslaught, found here:
+// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
+
+
+#if CONFIG_TAPE_TURBO
+
+
+tape_turbo_get_bit:
+
+	lda #$10	
+!:
+	bit CIA1_ICR // $DC0D	
+	beq !-                             // busy loop to detect signal
+	lda CIA2_ICR // $DD0D
+	pha
+	lda #%00011001                     // start timer, one-shot, force latch reload
+	sta CIA2_CRA // $DD0E	
+	pla
+	
+	pha                                // audio/video effects
+	asl
+	sta SID_SIGVOL
+	beq !+
+#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
+	lda #$0B
+#else
+	lda #$06
+#endif
+!:
+	sta VIC_EXTCOL
+	pla
+
+	lsr
+	rts
+
+
+#endif // CONFIG_TAPE_TURBO

c64/kernal/tape/tape_turbo_get_byte.s

@@ -0,0 +1,26 @@
+
+//
+// Tape (turbo) helper routine - byte reading
+//
+
+// Based on routine by enthusi/Onslaught, found here:
+// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
+
+
+#if CONFIG_TAPE_TURBO
+
+
+tape_turbo_get_byte:
+
+	lda #$01
+	sta ROPRTY                         // init the to-be-read byte with 1 (canary bit to mark loop end)
+!:
+	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
+
+
+#endif // CONFIG_TAPE_TURBO

c64/kernal/tape/tape_turbo_sync.s

@@ -0,0 +1,56 @@
+
+//
+// Tape (turbo) helper routine - synchronization handling
+//
+
+// Based on routine by enthusi/Onslaught, found here:
+// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
+
+
+#if CONFIG_TAPE_TURBO
+
+
+tape_turbo_sync_common:
+
+	jsr tape_turbo_get_bit 
+	rol ROPRTY
+	lda ROPRTY
+	cmp #$02
+	bne tape_turbo_sync_common
+	rts
+
+tape_turbo_sync_header:
+
+	ldx #$FF
+!:
+	ldy #$03
+!:
+	jsr tape_turbo_sync_common
+	dey
+	bne !-
+	dex
+	bne !--
+
+	// FALLTROUGH
+
+tape_turbo_sync_payload:
+
+	jsr tape_turbo_sync_common
+!:
+	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 !-
+ 	ldy #$00
+!: 
+	cpx ROPRTY
+	bne tape_turbo_sync_payload
+	jsr tape_turbo_get_byte
+	dex
+	bne !-
+
+	rts 
+
+
+#endif // CONFIG_TAPE_TURBO