From 9fb08e045ae07cf354e707195e5221cca5d31479 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Josef=20S=C3=B6ntgen?= <josef.soentgen@genode-labs.com>
Date: Thu, 17 Dec 2015 18:56:34 +0100
Subject: [PATCH] libports: fix delay in SDL audio backend

Instead of using the 'alloc()' method to allocate new packets use
the 'next()' method with the previous packet. This is needed because
the last audio stack changes broke the semantics assumed by 'alloc()'.

We now keep track of the already queued packets by hand.

Fixes #1827.
---
 .../src/lib/sdl/audio/SDL_genodeaudio.cc      | 71 +++++++++++--------
 1 file changed, 40 insertions(+), 31 deletions(-)

diff --git a/repos/libports/src/lib/sdl/audio/SDL_genodeaudio.cc b/repos/libports/src/lib/sdl/audio/SDL_genodeaudio.cc
index b0ad2d0ff8..ac70bee2fb 100644
--- a/repos/libports/src/lib/sdl/audio/SDL_genodeaudio.cc
+++ b/repos/libports/src/lib/sdl/audio/SDL_genodeaudio.cc
@@ -56,6 +56,7 @@ struct SDL_PrivateAudioData {
 	Uint8             *mixbuf;
 	Uint32             mixlen;
 	Audio_out::Connection *audio[AUDIO_CHANNELS];
+	Audio_out::Packet     *packet[AUDIO_CHANNELS];
 };
 
 
@@ -146,7 +147,8 @@ static SDL_AudioDevice *GENODEAUD_CreateDevice(int devindex)
 	for (int channel = 0; channel < AUDIO_CHANNELS; channel++) {
 		try {
 			_this->hidden->audio[channel] = new (env()->heap())
-				Audio_out::Connection(channel_names[channel]);
+				Audio_out::Connection(channel_names[channel],
+				                      false, channel == 0 ? true : false);
 			_this->hidden->audio[channel]->start();
 		} catch(Genode::Parent::Service_denied) {
 			PERR("Could not connect to 'Audio_out' service.");
@@ -171,47 +173,48 @@ AudioBootStrap GENODEAUD_bootstrap = {
 };
 
 
-/* This function waits until it is possible to write a full sound buffer */
 static void GENODEAUD_WaitAudio(_THIS)
 {
-	for (int channel = 0; channel < AUDIO_CHANNELS; channel++) {
-		Audio_out::Connection *connection = _this->hidden->audio[channel];
+	Audio_out::Connection *con = _this->hidden->audio[0];
+	Audio_out::Packet     *p   = _this->hidden->packet[0];
 
-		/* wait until allocation is possible */
-		if (connection->stream()->full())
-			connection->wait_for_alloc();
+	unsigned const packet_pos = con->stream()->packet_position(p);
+	unsigned const play_pos   = con->stream()->pos();
+	unsigned queued           = packet_pos < play_pos
+	                            ? ((Audio_out::QUEUE_SIZE + packet_pos) - play_pos)
+	                            : packet_pos - play_pos;
+
+	/* wait until there is only one packet left to play */
+	while (queued > 1) {
+		con->wait_for_progress();
+		queued--;
 	}
 }
 
 
 static void GENODEAUD_PlayAudio(_THIS)
 {
-	/*
-	 * Synchronize the play pointer when this function is first called
-	 */
-	static bool initial_reset = true;
-	if (initial_reset) {
-		for (int channel = 0; channel < AUDIO_CHANNELS; channel++) {
-			Audio_out::Connection *connection = _this->hidden->audio[channel];
-			connection->stream()->reset();
-		}
-		initial_reset = false;
+	Audio_out::Connection *c[AUDIO_CHANNELS];
+	Audio_out::Packet     *p[AUDIO_CHANNELS];
+	for (int channel = 0; channel < AUDIO_CHANNELS; channel++) {
+		c[channel] = _this->hidden->audio[channel];
+		p[channel] = _this->hidden->packet[channel];
 	}
 
-	Audio_out::Packet *p[AUDIO_CHANNELS];
+	/* get the currently played packet initially */
+	static bool init = false;
+	if (!init) {
+		p[0] = c[0]->stream()->next();
+		init = true;
+	}
 
-	for (int channel = 0; channel < AUDIO_CHANNELS; channel++)
-		while (1) {
-			Audio_out::Connection *connection = _this->hidden->audio[channel];
-
-			try {
-				p[channel] = connection->stream()->alloc();
-				break;
-			} catch (Audio_out::Stream::Alloc_failed) {
-				/* wait for next finished packet */
-				connection->wait_for_alloc();
-			}
-		}
+	/*
+	 * Get new packet for left channel and use it to synchronize
+	 * the right channel
+	 */
+	p[0] = c[0]->stream()->next(p[0]);
+	unsigned ppos = c[0]->stream()->packet_position(p[0]);
+	p[1] = c[1]->stream()->get(ppos);
 
 	if (signal_receiver()->pending()) {
 		signal_receiver()->wait_for_signal();
@@ -224,8 +227,14 @@ static void GENODEAUD_PlayAudio(_THIS)
 			p[channel]->content()[sample] =
 				volume * (float)(((int16_t*)_this->hidden->mixbuf)[sample * AUDIO_CHANNELS + channel]) / 32768;
 
-	for (int channel = 0; channel < AUDIO_CHANNELS; channel++)
+	for (int channel = 0; channel < AUDIO_CHANNELS; channel++) {
 		_this->hidden->audio[channel]->submit(p[channel]);
+		/*
+		 * Save current packet to query packet position next time and
+		 * when in GENODEAUD_WaitAudio
+		 */
+		_this->hidden->packet[channel] = p[channel];
+	}
 }