From 89772839f4a09e8e12d0bc95d5e791d7039b1249 Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@gmail.com>
Date: Tue, 16 Apr 2024 18:45:43 +0200
Subject: [PATCH] synchronize using sync pulses

---
 .../main/java/xdsopl/robot36/Demodulator.java | 15 +++---
 .../java/xdsopl/robot36/MainActivity.java     | 50 +++++++++++++------
 2 files changed, 43 insertions(+), 22 deletions(-)

diff --git a/app/src/main/java/xdsopl/robot36/Demodulator.java b/app/src/main/java/xdsopl/robot36/Demodulator.java
index 3171236..784c08c 100644
--- a/app/src/main/java/xdsopl/robot36/Demodulator.java
+++ b/app/src/main/java/xdsopl/robot36/Demodulator.java
@@ -26,6 +26,8 @@ public class Demodulator {
 	private Complex syncPulse;
 	private Complex scanLine;
 
+	public int syncPulseOffset;
+
 	Demodulator(int sampleRate) {
 		double powerWindowSeconds = 0.5;
 		int powerWindowSamples = (int) Math.round(powerWindowSeconds * sampleRate) | 1;
@@ -61,7 +63,8 @@ public class Demodulator {
 		scanLine = new Complex();
 	}
 
-	public void process(float[] buffer) {
+	public boolean process(float[] buffer) {
+		boolean syncPulseDetected = false;
 		for (int i = 0; i < buffer.length; ++i) {
 			baseBand = baseBandLowPass.avg(baseBand.set(buffer[i]).mul(baseBandOscillator.rotate()));
 			syncPulse = syncPulseFilter.avg(syncPulse.set(baseBand).mul(syncPulseOscillator.rotate()));
@@ -76,19 +79,17 @@ public class Demodulator {
 					syncPulseMaxPosition = syncPulseCounter;
 				}
 				++syncPulseCounter;
-				buffer[i] = syncPulseLevel;
 			} else if (syncPulseCounter > 0 && syncPulseCounter < syncPulseSamples) {
-				int offset = syncPulseCounter - syncPulseMaxPosition;
-				if (offset <= i)
-					buffer[i - offset] = -1;
+				syncPulseOffset = i + syncPulseMaxPosition - syncPulseCounter;
+				syncPulseDetected = true;
 				syncPulseCounter = 0;
 				syncPulseMaxLevel = 0;
-				buffer[i] = scanLineLevel;
 			} else {
 				syncPulseCounter = 0;
 				syncPulseMaxLevel = 0;
-				buffer[i] = scanLineLevel;
 			}
+			buffer[i] = scanLineLevel;
 		}
+		return syncPulseDetected;
 	}
 }
diff --git a/app/src/main/java/xdsopl/robot36/MainActivity.java b/app/src/main/java/xdsopl/robot36/MainActivity.java
index 8a4f9e8..8666bbb 100644
--- a/app/src/main/java/xdsopl/robot36/MainActivity.java
+++ b/app/src/main/java/xdsopl/robot36/MainActivity.java
@@ -42,6 +42,7 @@ public class MainActivity extends AppCompatActivity {
 	private int tint;
 	private int curLine;
 	private int curColumn;
+	private int syncPulseToleranceSamples;
 
 	private void setStatus(int id) {
 		status.setText(id);
@@ -55,30 +56,49 @@ public class MainActivity extends AppCompatActivity {
 		@Override
 		public void onPeriodicNotification(AudioRecord audioRecord) {
 			audioRecord.read(recordBuffer, 0, recordBuffer.length, AudioRecord.READ_BLOCKING);
-			demodulator.process(recordBuffer);
-			visualizeSignal();
+			visualizeSignal(demodulator.process(recordBuffer));
 		}
 	};
 
-	private void visualizeSignal() {
+	private void slideUpOneLine() {
+		for (int i = 0; i < scopeWidth; ++i)
+			scopePixels[scopeWidth * (curLine + scopeHeight) + i] = scopePixels[scopeWidth * curLine + i];
+		curLine = (curLine + 1) % scopeHeight;
+		scopeBitmap.setPixels(scopePixels, scopeWidth * curLine, scopeWidth, 0, 0, scopeWidth, scopeHeight);
+		scopeView.invalidate();
+	}
+
+	private void visualizeSignal(boolean syncPulseDetected) {
+		int syncPulseOffset = curColumn + demodulator.syncPulseOffset;
+		if (syncPulseDetected && syncPulseOffset >= syncPulseToleranceSamples && syncPulseOffset < curColumn) {
+			syncPulseDetected = false;
+			int nextLine = (curLine + 1) % scopeHeight;
+			for (int i = 0; i < curColumn - syncPulseOffset; ++i)
+				scopePixels[scopeWidth * nextLine + i] = scopePixels[scopeWidth * curLine + syncPulseOffset + i];
+			for (int i = syncPulseOffset; i < scopeWidth; ++i)
+				scopePixels[scopeWidth * curLine + i] = 0xff00ff00;
+			curColumn -= syncPulseOffset;
+			slideUpOneLine();
+		}
 		for (float v : recordBuffer) {
-			int pixelColor = 0xff00ff00;
-			if (v >= 0) {
-				int intensity = (int) Math.round(255 * Math.sqrt(v));
-				pixelColor = 0xff000000 | 0x00010101 * intensity;
-			}
+			int intensity = (int) Math.round(255 * Math.sqrt(v));
+			int pixelColor = 0xff000000 | 0x00010101 * intensity;
 			scopePixels[scopeWidth * curLine + curColumn] = pixelColor;
-			if (++curColumn >= scopeWidth) {
+			boolean syncNow = syncPulseDetected && syncPulseOffset == curColumn;
+			if (syncNow || ++curColumn >= scopeWidth) {
+				syncPulseDetected = false;
 				curColumn = 0;
-				for (int i = 0; i < scopeWidth; ++i)
-					scopePixels[scopeWidth * (curLine + scopeHeight) + i] = scopePixels[scopeWidth * curLine + i];
-				curLine = (curLine + 1) % scopeHeight;
-				scopeBitmap.setPixels(scopePixels, scopeWidth * curLine, scopeWidth, 0, 0, scopeWidth, scopeHeight);
-				scopeView.invalidate();
+				slideUpOneLine();
 			}
 		}
 	}
 
+	void initTools(int sampleRate) {
+		demodulator = new Demodulator(sampleRate);
+		double syncPulseToleranceSeconds = 0.001;
+		syncPulseToleranceSamples = (int) Math.round(syncPulseToleranceSeconds * sampleRate);
+	}
+
 	private void initAudioRecord() {
 		int audioSource = MediaRecorder.AudioSource.UNPROCESSED;
 		int channelConfig = AudioFormat.CHANNEL_IN_MONO;
@@ -95,7 +115,7 @@ public class MainActivity extends AppCompatActivity {
 			if (audioRecord.getState() == AudioRecord.STATE_INITIALIZED) {
 				audioRecord.setRecordPositionUpdateListener(recordListener);
 				audioRecord.setPositionNotificationPeriod(recordBuffer.length);
-				demodulator = new Demodulator(sampleRate);
+				initTools(sampleRate);
 				startListening();
 			} else {
 				setStatus(R.string.audio_init_failed);