From e9b9767a71b1177109e9a78c0d3c70ebea1e5b2d Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Mon, 20 Jan 2020 21:13:22 +0100
Subject: [PATCH] tape speed adjustments for normal load works now

---
 c64/kernal/tape/tape_normal_calibrate.s | 64 ++++++++++++++++++++-----
 c64/kernal/tape/tape_normal_get_pilot.s |  7 +--
 2 files changed, 53 insertions(+), 18 deletions(-)

diff --git a/c64/kernal/tape/tape_normal_calibrate.s b/c64/kernal/tape/tape_normal_calibrate.s
index d5274d2c..5a517018 100644
--- a/c64/kernal/tape/tape_normal_calibrate.s
+++ b/c64/kernal/tape/tape_normal_calibrate.s
@@ -12,38 +12,42 @@
 #if CONFIG_TAPE_NORMAL
 
 
-tape_normal_calibrate_during_pilot:    // reecalibration during the pilot
+tape_normal_calibrate_during_pilot:              // reecalibration during the pilot
 
 	sta __normal_time_S
 
 	// We do not have any recent medium pulse measurement,
 	// probably the only solution is to estimate it
 
-	lda $FF
+	lda #$FF
 	sec
 	sbc __normal_time_S
 
 	// We now have a difference from the starting point ($FF)
 
 	clc
-	rol
-	sta __normal_time_M                // this is temporary only!
+	ror
+	sta __normal_time_M                          // this is temporary only!
 
 	// We now have half the difference, substract it from
 	// short pulse measurement result
 
 	lda __normal_time_S
-	clc
+	sec
 	sbc __normal_time_M
+	
+	// Add a small correction to gain $7D if starting from $A5. Dirty, ugly,
+	// and imprecise hack - but in real life should be good enough
 
-	// XXX add some constant to get a proper __normal_time_M ($7D if starting from $A5), afterwards remove __normal_time_M initialization from tape_normal_get_pilot_header
-
-	sta __normal_time_M
+	clc
+	adc #$05
+	sta __normal_time_M                          // estimated medium pulse length
 
 	jmp tape_normal_calibrate_common
 
 
-tape_normal_calibrate_after_S:         // recalibration after short pulse
+
+tape_normal_calibrate_after_S:                   // recalibration after short pulse
 
 	sta __normal_time_S
 	rts
@@ -51,7 +55,7 @@ tape_normal_calibrate_after_S:         // recalibration after short pulse
 
 	// FALLTROUGH
 
-tape_normal_calibrate_after_M:         // recalibration after medium pulse
+tape_normal_calibrate_after_M:                   // recalibration after medium pulse
 
 	sta __normal_time_M
 
@@ -68,14 +72,50 @@ tape_normal_calibrate_common:
 	adc __normal_time_M
 
 	cmp __pulse_threshold
-	beq tape_normal_calibrate_done     // branch if no recalibration needed
+
+	beq tape_normal_calibrate_done               // branch if no recalibration needed
+
+	// Correct the thresholds (default is $91 for the S/M one)
+
+	bcs tape_normal_calibrate_threshold_inc      // branch if .A >= memory
+
+	// FALLTROUGH
 
 
+tape_normal_calibrate_threshold_dec:
 
-	// XXX implement recalibration
+	lda __pulse_threshold
+	cmp #($91-10)
+	bcc tape_normal_calibrate_done               // do not decrement thresholds too far
+
+	sec
+	sbc #$02
+	sta __pulse_threshold
+
+	lda __pulse_threshold_ML
+	sec
+	sbc #$03
+	sta __pulse_threshold_ML
+
+	bne tape_normal_calibrate_done               // branch always
 
 
+tape_normal_calibrate_threshold_inc:
 
+	lda __pulse_threshold
+	cmp #($91+11)
+	bcs tape_normal_calibrate_done               // do not increment thresholds too far
+
+	clc
+	adc #$02
+	sta __pulse_threshold
+
+	lda __pulse_threshold_ML
+	clc
+	adc #$03
+	sta __pulse_threshold_ML
+
+	// FALLTROUGH
 
 
 tape_normal_calibrate_done:
diff --git a/c64/kernal/tape/tape_normal_get_pilot.s b/c64/kernal/tape/tape_normal_get_pilot.s
index 11c17c0b..801a2fb1 100644
--- a/c64/kernal/tape/tape_normal_get_pilot.s
+++ b/c64/kernal/tape/tape_normal_get_pilot.s
@@ -21,18 +21,14 @@
 tape_normal_get_pilot_header:          // entry point, reset calibration, require 128x $40 pulses
 
 	// Reading the pilot header is the first action performed,
-	// thus start by setting default timings, as measured during
-	// VICE test
+	// thus start by setting default thresholds
 
-	lda #$7D
-	sta __normal_time_M                // __normal_time_S will be set within the pilot
 	lda #$91
 	sta __pulse_threshold
 	lda #$67
 	sta __pulse_threshold_ML
 
 	lda #$80
-
 	skip_2_bytes_trash_nvz
 
 	// FALLTROUGH
@@ -40,7 +36,6 @@ tape_normal_get_pilot_header:          // entry point, reset calibration, requir
 tape_normal_get_pilot_data:            // entry point, require 4x $40 pulses
 
 	lda #$04
-
 	skip_2_bytes_trash_nvz
 
 	// FALLTROUGH