turbo tape now adjusts it's reading speed dynamically

CONFIG.md

@@ -155,12 +155,6 @@ Adds a minimal turbo tape support - just LOAD command (device 7, like on _Action
 
 Needs about 650 bytes in KERNAL segment (if both normal and turbo are enabled, about 950 bytes are needed, as they share some code). If unsure - enable.
 
-### `CONFIG_TAPE_TURBO_AUTOCALIBRATE`
-
-Extends the tape turbo load functionality by ability to adjust to tape speed differences.
-
-Needs about 100 bytes in KERNAL segment. If unsure - enable for Datasette or other tape recorder, disable for digital solutions like Tapuino.
-
 ### `CONFIG_TAPE_NO_KEY_SENSE`
 
 Enable this option if you are using a tape interface adapter with some audio signal source connected. These adapters lack key sense functionality, so the computer is unable to tell whether Play got pressed or not - with this option ROM will assume Play got pressed after imppulses start arriving from the tape.

STATUS.md

@@ -11,7 +11,7 @@ Here are the features of the Open ROMs not found in the original ROMs from the 8
 * JiffyDOS and DolphinDOS protocols support
 * DOS wedge (direct mode only) - `@<drive_number>`, `@<command>`, `@$`, `@$<params>`, `@`
 
-* turbo tape load support (as device 7, or using `←L`), quite sophisticated: up to 250 blocks (can store bytes under I/O), can use sync signal for autocalibration (less load errors than simple turbos)
+* turbo tape load support (as device 7, or using `←L`), quite sophisticated: up to 250 blocks (can store bytes under I/O), automatically adjusts for tape speed differences
 * improved support for tape adapters (for using regular casette players and other audio devices instead of Datasette)
 
 * extended `LOAD` command

c64/,,config_custom.s

@@ -56,7 +56,6 @@
 
 #define CONFIG_TAPE_NORMAL
 #define CONFIG_TAPE_TURBO
-#define CONFIG_TAPE_TURBO_AUTOCALIBRATE
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/,,config_generic.s

@@ -50,7 +50,6 @@
 
 #define CONFIG_TAPE_NORMAL
 #define CONFIG_TAPE_TURBO
-#define CONFIG_TAPE_TURBO_AUTOCALIBRATE
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/,,config_mega65.s

@@ -50,7 +50,6 @@
 
 // #define CONFIG_TAPE_NORMAL
 // #define CONFIG_TAPE_TURBO
-// #define CONFIG_TAPE_TURBO_AUTOCALIBRATE
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/,,config_testing.s

@@ -50,7 +50,6 @@
 
 // #define CONFIG_TAPE_NORMAL
 #define CONFIG_TAPE_TURBO
-// #define CONFIG_TAPE_TURBO_AUTOCALIBRATE
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/,,config_ultimate64.s

@@ -50,7 +50,6 @@
 
 #define CONFIG_TAPE_NORMAL
 #define CONFIG_TAPE_TURBO
-#define CONFIG_TAPE_TURBO_AUTOCALIBRATE
 // #define CONFIG_TAPE_NO_KEY_SENSE
 // #define CONFIG_TAPE_NO_MOTOR_CONTROL
 

c64/aliases/,aliases_ram_lowmem.s

@@ -88,7 +88,7 @@
 	.label VERCKK    = $93  //          0 = LOAD, 1 = VERIFY
 	.label C3PO      = $94  //          flag - is BSOUR content valid
 	.label BSOUR     = $95  //          serial bus buffered output byte
-	.label SYNO      = $96  //          -- NOT IMPLEMENTED --
+	.label SYNO      = $96  //          temporary tape routines storage, [!] our usage differs
 	.label XSAV      = $97  //          temporary register storage for ASCII/tape related routines [!] usage details might differ
 	.label LDTND     = $98  //          number of entries in LAT / FAT / SAT tables
 	.label DFLTN     = $99  //          default input device

c64/kernal/tape/tape_common_prepare_cia.s

@@ -2,6 +2,37 @@
 // #LAYOUT# *   KERNAL_0 #TAKE
 // #LAYOUT# *   *        #IGNORE
 
+//
+// Prepare CIA timers for tape reading
+//
+
+//
+// Checked under VICE, PAL, average of 256 pulses:
+//
+//     normal - short  - timer goes down to $C9
+//     normal - medium - timer goes down to $79
+//     normal - long   - timer goes down to $52
+//
+//     turbo  - short  - timer goes down to $B1
+//     turbo  - long   - timer goes down to $CD
+//
+//
+// Measurement subroutine: .A should contain timer value, $C000-$C002 zeroed
+//
+//        clc
+//        adc $C001
+//        sta $C001
+//        bcc !+
+//        inc $C000
+//    !:
+//	      inc $C002
+//	      beq !+
+//	      rts
+//    !:
+//	      lda $C000
+//	  .break         // .A contains our average
+//        rts
+//
 
 #if CONFIG_TAPE_NORMAL || CONFIG_TAPE_TURBO
 

c64/kernal/tape/tape_turbo_get_bit.s

@@ -31,16 +31,13 @@ tape_turbo_get_bit:
 
 #endif
 
-
+	cmp SYNO                           // threshold
-#if CONFIG_TAPE_TURBO_AUTOCALIBRATE
-	tax
-	cmp IRQTMP+0
-#else
-	cmp #$BF                           // threshold calculated by autocalibration routines under VICE
-#endif
-
 	bcs !+
 
+	clc
+	ror
+	sta IRQTMP+0                       // store half of the last measurement result for short pulse
+
 	lda #$01
 	sta SID_SIGVOL
 	lda #$06
@@ -48,6 +45,10 @@ tape_turbo_get_bit:
 	sec
 	rts
 !:
+	clc
+	ror
+	sta IRQTMP+1                       // store half of the last measurement result for long pulse
+
 	lda #$00
 	sta SID_SIGVOL
 	sta VIC_EXTCOL

c64/kernal/tape/tape_turbo_get_byte.s

@@ -25,8 +25,35 @@ tape_turbo_get_byte:
 	rol INBIT
 	bcc !-	                           // is the initial 1 shifted into carry already?
 	plx_trash_a
-	lda INBIT
 
+	// Compensate for tape speed variations
+
+	lda IRQTMP+0                       // half of the last value for bit '0'
+	clc
+	adc IRQTMP+1                       // half of the last value for bit '1'
+	
+	sec
+	sbc SYNO                           // now we have a diff between current threshold and calculated one
+	beq tape_turbo_get_byte_done       // branch if threshold correction not needed
+
+	bpl !+
+
+	lda SYNO
+	cmp #($BF - 10)
+	beq tape_turbo_get_byte_done       // do not decrease threshold too far no matter what
+
+	dec SYNO
+	bne tape_turbo_get_byte_done       // branch always
+!:
+	lda SYNO
+	cmp #($BF + 10)
+	beq tape_turbo_get_byte_done       // do not increase threshold too far no matter what
+
+	inc SYNO
+
+tape_turbo_get_byte_done:
+
+	lda INBIT
 	rts
 
 

c64/kernal/tape/tape_turbo_sync.s

@@ -15,8 +15,9 @@
 
 tape_turbo_sync_header:
 
-
+	// Initial pulse threshold
-#if !CONFIG_TAPE_TURBO_AUTOCALIBRATE
+	lda #$BF                           // measured 128 bits '0' and 128 bits '1' under VICE, calculated average
+	sta SYNO
 
 	// Synchronize with start of sync sequence
 	jsr tape_turbo_sync_first
@@ -24,106 +25,19 @@ tape_turbo_sync_header:
 	// Perform synchronization, double loop, total $C0 * $04 iterations
 	ldx #$C0
 !:
-	phx_trash_a
 	ldy #$04
 !:
+	stx XSAV
 	jsr tape_turbo_get_byte
 	cmp #$02
 	bne tape_turbo_sync_header         // branch if failure
 
 	dey
 	bne !-
-	plx_trash_a
+	ldx XSAV
 	dex
 	bne !--
 
-#else // CONFIG_TAPE_TURBO_AUTOCALIBRATE
-
-	// Initial pulse threshold
-	lda #$BF // auto-calibration under VICE often returns this value
-	sta IRQTMP+0
-
-	// Zero temporary stack area
-	lda #$00
-	ldy #$03
-!:
-	sta STACK, y
-	dey
-	bpl !-
-
-	// Synchronize with start of sync sequence
-	jsr tape_turbo_sync_first
-
-	// Perform synchronization, get measurements from 128 bytes
-	ldx #$10
-
-	// FALLTROUGH
-
-tape_turbo_sync_outer_loop:
-
-    // Set .Y (inner loop counter) to $28-$38, average $30; $10 * $30 equals $C0 * $04
-	// We want a bit of irregularity with byte selection for calibration
-	txa
-	pha                                          // store .X
-	clc
-	adc #$27
-	tay
-	
-	// FALLTROUGH
-
-tape_turbo_sync_inner_loop:
-
-	cpy #$09
-	bcc !+                                       // if inner couter is 8 or lower, get this byte for measurement
-
-	// Get byte without measurements
-	jsr tape_turbo_get_byte
-	cmp #$02
-	bne tape_turbo_sync_header                   // branch if failure
-	beq tape_turbo_sync_header_next_iter         // branch always
-	
-!:
-	// Get byte and take measurements
-
-	phy_trash_a
-
-	// Skip 5 bits, they should be all 0
-	ldy #$04
-!:
-	jsr tape_turbo_get_bit
-	bcs tape_turbo_sync_header
-	dey
-	bpl !-
-
-	// Get measurements from 3 bits
-	jsr tape_turbo_sync_measure_0
-	jsr tape_turbo_sync_measure_1
-	jsr tape_turbo_sync_measure_0
-
-	ply_trash_a
-
-	// FALLTROUGH
-
-tape_turbo_sync_header_next_iter:
-
-	dey
-	bne tape_turbo_sync_inner_loop
-	plx_trash_a
-	dex
-	bne tape_turbo_sync_outer_loop
-
-	// Calculate new pulse threshold as arithmetic mean
-	// We accumulated 256 zeros and 128 ones, so calculating average value is easy
-
-	lda STACK+0
-	clc
-	ror
-	clc
-	adc STACK+1
-	sta IRQTMP+0
-
-#endif // CONFIG_TAPE_TURBO_AUTOCALIBRATE
-
 	// FALLTROUGH
 
 tape_turbo_sync_payload: