From 82b4f8a58951dd41776b0d9e4ccdd9cd4f319cda Mon Sep 17 00:00:00 2001
From: Matthias Ringwald <matthias@ringwald.ch>
Date: Tue, 28 Dec 2021 21:38:41 +0100
Subject: [PATCH] example/audio_duplex: avoid noise on start

---
 example/audio_duplex.c | 88 ++++++++++++++++++++++--------------------
 1 file changed, 47 insertions(+), 41 deletions(-)

diff --git a/example/audio_duplex.c b/example/audio_duplex.c
index d5f48fa50..3286d4d53 100644
--- a/example/audio_duplex.c
+++ b/example/audio_duplex.c
@@ -71,7 +71,7 @@ static btstack_ring_buffer_t audio_buffer;
 static int16_t transfer_buffer[TRANSFER_SAMPLES * NUM_INPUT_CHANNELS];
 
 // playback starts after audio_buffer is half full
-static int playback_started;
+static bool playback_started;
 
 // sample couners
 static int count_recording;
@@ -87,51 +87,57 @@ static void audio_recording(const int16_t * pcm_buffer, uint16_t num_samples_to_
 
 static void audio_playback(int16_t * pcm_buffer, uint16_t num_samples_to_write){
     int num_samples_in_buffer = btstack_ring_buffer_bytes_available(&audio_buffer) / BYTES_PER_SAMPLE;
-    if (playback_started == 0){
-        if ( num_samples_in_buffer < (BUFFER_SAMPLES / 2)) return;
-        playback_started = 1;
+    if (playback_started == false){
+        if ( num_samples_in_buffer >= (BUFFER_SAMPLES / 2)){
+            playback_started = true;
+        }
     }
     count_playback += num_samples_to_write;
-    while (num_samples_to_write){
-        num_samples_in_buffer = btstack_ring_buffer_bytes_available(&audio_buffer) / BYTES_PER_SAMPLE;
-        int num_samples_ready = btstack_min(num_samples_in_buffer, num_samples_to_write);
-        // limit by transfer_buffer
-        int num_samples_from_buffer = btstack_min(num_samples_ready, TRANSFER_SAMPLES);
-        if (!num_samples_from_buffer) break;
-        uint32_t bytes_read;
-        btstack_ring_buffer_read(&audio_buffer, (uint8_t *) transfer_buffer, num_samples_from_buffer * BYTES_PER_SAMPLE, &bytes_read);
-#if (NUM_INPUT_CHANNELS == 1)
-        // duplicate samples for stereo output
-        int i;
-        for (i=0; i < num_samples_from_buffer;i++) {
-            *pcm_buffer++ = transfer_buffer[i];
-            *pcm_buffer++ = transfer_buffer[i];
-            num_samples_to_write--;
-        }
-#endif
-#if (NUM_INPUT_CHANNELS == 2)
-        // copy samples
-        int i;
-        int j = 0;
-        for (i=0; i < num_samples_from_buffer;i++) {
-            *pcm_buffer++ = transfer_buffer[j++];
-            *pcm_buffer++ = transfer_buffer[j++];
-            num_samples_to_write--;
-        }
-#endif
-    }
 
-    // warn about underrun
-    if (num_samples_to_write){
-        printf("Buffer underrun - recording %u, playback %u - delta %d!\n", count_recording, count_playback, count_recording - count_playback);
+    if (playback_started){
+
+        while (num_samples_to_write){
+
+            num_samples_in_buffer = btstack_ring_buffer_bytes_available(&audio_buffer) / BYTES_PER_SAMPLE;
+            int num_samples_ready = btstack_min(num_samples_in_buffer, num_samples_to_write);
+            // limit by transfer_buffer
+            int num_samples_from_buffer = btstack_min(num_samples_ready, TRANSFER_SAMPLES);
+            if (!num_samples_from_buffer) break;
+            uint32_t bytes_read;
+            btstack_ring_buffer_read(&audio_buffer, (uint8_t *) transfer_buffer, num_samples_from_buffer * BYTES_PER_SAMPLE, &bytes_read);
+
+#if (NUM_INPUT_CHANNELS == 1)
+            // duplicate samples for stereo output
+            int i;
+            for (i=0; i < num_samples_from_buffer;i++) {
+                *pcm_buffer++ = transfer_buffer[i];
+                *pcm_buffer++ = transfer_buffer[i];
+                num_samples_to_write--;
+            }
+#endif
+
+#if (NUM_INPUT_CHANNELS == 2)
+            // copy samples
+            int i;
+            int j = 0;
+            for (i=0; i < num_samples_from_buffer;i++) {
+                *pcm_buffer++ = transfer_buffer[j++];
+                *pcm_buffer++ = transfer_buffer[j++];
+                num_samples_to_write--;
+            }
+#endif
+
+        }
+
+        // warn about underrun
+        if (num_samples_to_write){
+            printf("Buffer underrun - recording %u, playback %u - delta %d!\n", count_recording, count_playback, count_recording - count_playback);
+        }
+
     }
 
     // fill rest with silence
-    while (num_samples_to_write){
-        *pcm_buffer++ = 0;
-        *pcm_buffer++ = 0;
-        num_samples_to_write--;
-    }
+    memset(pcm_buffer, 0, num_samples_to_write * 4);
 }
 
 static void start_loopback(btstack_timer_source_t * ts){
@@ -174,7 +180,7 @@ static void stop_loopback(btstack_timer_source_t * ts){
     audio_sink->close();
     audio_source->close();
 
-    playback_started = 0;
+    playback_started = false;
 
     printf("Stop Audio Loopback\n");