started work on tape format autodetection

c64/,,config_custom.s

@@ -56,6 +56,7 @@
 
 #define CONFIG_TAPE_NORMAL
 #define CONFIG_TAPE_TURBO
+#define CONFIG_TAPE_AUTODETECT         // not fully done yet!
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/kernal/tape/load_tape_normal.s

@@ -44,6 +44,28 @@ load_tape_normal:
 
 	jsr tape_ditch_verify              // only LOAD is supported, no VERIFY
 
+#if CONFIG_TAPE_TURBO && CONFIG_TAPE_AUTODETECT
+
+	// Prepare for sound effects in case of turbo takeover
+	jsr tape_clean_sid
+
+#endif
+
+	// Start playing
+	jsr tape_common_prepare_cia
+	jsr tape_ask_play
+
+#if CONFIG_TAPE_TURBO && CONFIG_TAPE_AUTODETECT
+
+	// FALLTROUGH
+
+load_tape_normal_takeover:             // entry point for turbo->normal takeover
+
+	jsr tape_common_autodetect
+	bcs_16 load_tape_turbo_takeover
+
+#endif
+
 	// Temporarily store MEMUSS in EAL
 
 	lda MEMUSS+1
@@ -51,11 +73,6 @@ load_tape_normal:
 	lda MEMUSS+0
 	sta EAL+0
 
-	// Start playing
-
-	jsr tape_common_prepare_cia
-	jsr tape_ask_play
-
 	// FALLTROUGH
 
 load_tape_normal_header:

c64/kernal/tape/load_tape_turbo.s

@@ -27,6 +27,17 @@ load_tape_turbo:
 
 	// FALLTROUGH
 
+#if CONFIG_TAPE_NORMAL && CONFIG_TAPE_AUTODETECT
+
+load_tape_turbo_takeover:             // entry point for turbo->normal takeover
+
+	jsr tape_common_autodetect
+	bcc_16 load_tape_normal_takeover
+
+#endif
+
+	// FALLTROUGH
+
 load_tape_turbo_header:
 
 	// Read file header; structure described here:

c64/kernal/tape/tape_common_autodetect.s

@@ -0,0 +1,101 @@
+// #LAYOUT# STD *        #TAKE
+// #LAYOUT# *   KERNAL_0 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+//
+// Tries to detect
+//
+// Carry clear - NORMAL, Carry set - TURBO
+//
+
+// XXX implement fallback to autodetection, correct screen color for NORMAL
+
+
+#if CONFIG_TAPE_NORMAL && CONFIG_TAPE_TURBO && CONFIG_TAPE_AUTODETECT
+
+
+tape_common_autodetect:
+
+	// Set screen color to something neutral, silence the audio
+
+	lda #$0C
+	sta VIC_EXTCOL
+	lda #$00
+	sta SID_SIGVOL
+
+	// FALLTROUGH
+
+tape_common_autodetect_retry:
+
+	// It is not trivial to distinguish between NORMAL and TURBO,
+	// as short pulses of NORMAL (and sync uses only shorts)
+    // have similar lengths as long pulses of TURBO
+
+	// Thus, the routine here reads certain amount of pulses
+	// looking for evidence for either NORMAL or TURBO system;
+	// in case of no evidence found, assume NORMAL
+
+	lda #$00                           // plus = probably NORMAL, minus = TURBO
+	sta XSAV
+
+	ldy #$60                           // $60 pulses cover 12 bytes of TURBO recording
+	jsr tape_normal_get_pulse          // first pulse might be a garbage, ignore it
+
+	// FALLTROUGH
+
+tape_common_autodetect_loop:
+
+	jsr tape_normal_get_pulse          // read pulse for detection attempt
+	
+	// If garbage found, retry detection
+	cmp #$28
+	bcc tape_common_autodetect_retry   // this is a VERY long pulse
+	cmp #$E8
+	bcs tape_common_autodetect_retry   // this is a VERY short pulse
+
+	// First try to distinguish TURBO short signal (reference: $CD)
+	// from NORMAL signals (reference: $A5 or lower), these values
+	// give us threshold of ($CD + $A5) / 2 = $B9
+
+	cmp #$B9
+	bcc !+
+	dec XSAV                           // above $B9 (so signal is shorter), looks like TURBO 
+!:
+	// Now try to distinguish TURBO signals (reference: $B1 or higher)
+	// from NORMAL medium/long signals (reference: $7D or below), these values
+	// give us threshold of ($B1 + $7D) / 2 = $97
+
+	cmp #$97
+	bcs !+
+	inc XSAV
+!:
+	// The sync for TURBO is not too long - if we have enough evidence,
+	// assume TURBO recording already
+
+	lda XSAV
+	cmp #$FD
+	beq tape_common_autodetect_turbo
+
+	// Next iteration
+	dey
+	bpl tape_common_autodetect_loop
+
+	// Last chance for TURBO
+
+	lda XSAV
+	bmi tape_common_autodetect_turbo
+
+	// FALLTROUGH
+
+tape_common_autodetect_normal:
+
+	clc
+	rts
+
+tape_common_autodetect_turbo:
+
+	sec
+	rts
+
+
+#endif

c64/kernal/tape/tape_common_prepare_cia.s

@@ -7,14 +7,14 @@
 //
 
 //
-// Checked under VICE, PAL, average of 256 pulses:
+// Checked under VICE, PAL, average of 256 pulses:  XXX retry measurements for NORMAL, something is probably wrong
 //
-//     normal - short  - timer goes down to $C9
+//     normal - short  - timer goes down to $A5
-//     normal - medium - timer goes down to $79
+//     normal - medium - timer goes down to $7D
 //     normal - long   - timer goes down to $52
 //
-//     turbo  - short  - timer goes down to $B1
+//     turbo  - short  - timer goes down to $CD
-//     turbo  - long   - timer goes down to $CD
+//     turbo  - long   - timer goes down to $B1
 //
 //
 // Measurement subroutine: .A should contain timer value, $C000-$C002 zeroed
@@ -58,3 +58,19 @@ tape_common_prepare_cia:
 	rts
 
 #endif
+
+
+xxx_measure:
+        clc
+        adc $C001
+        sta $C001
+        bcc !+
+        inc $C000
+    !:
+	      inc $C002
+	      beq !+
+	      rts
+    !:
+	      lda $C000
+	  .break         // .A contains our average
+        rts

c64/kernal/tape/tape_turbo_sync_measure.s

@@ -1,45 +0,0 @@
-// #LAYOUT# STD *        #TAKE
-// #LAYOUT# *   KERNAL_0 #TAKE
-// #LAYOUT# *   *        #IGNORE
-
-//
-// Tape (turbo) helper routine - measure bit length for calibration purposes
-//
-
-#if CONFIG_TAPE_TURBO && CONFIG_TAPE_TURBO_AUTOCALIBRATE
-
-
-tape_turbo_sync_measure_0:
-
-	// Measure bit '0'
-	jsr tape_turbo_get_bit
-	bcs tape_turbo_sync_measure_fail
-	txa
-	adc STACK+2
-	sta STACK+2
-	bcc !+
-	inc STACK+0
-!:
-	rts
-
-tape_turbo_sync_measure_1:
-
-	// Measure bit '1'
-	jsr tape_turbo_get_bit
-	bcc tape_turbo_sync_measure_fail
-	txa
-	adc STACK+3
-	sta STACK+3
-	bcc !+
-	inc STACK+1
-!:
-	rts
-
-tape_turbo_sync_measure_fail:
-
-	pla
-	pla
-	jmp tape_turbo_sync_header
-
-
-#endif