Mp3_audio_sink: mp3 audio playback as a Terminal service

Terminal server that decodes and queues MP3 encoded audio to an
Audio_out session. Mpg123 was selected as the decoder library for its
clean and well documented API, integrated resampler, and support for
32-bit floating point output.

Fix #101

recipes/src/mp3_audio_sink/content.mk

@@ -0,0 +1,2 @@
+SRC_DIR = src/app/mp3_audio_sink
+include $(GENODE_DIR)/repos/base/recipes/src/content.inc

recipes/src/mp3_audio_sink/hash

@@ -0,0 +1 @@
+2018-03-24 fe37ac4217462df71d74721c1ac22f7158ef210d

recipes/src/mp3_audio_sink/used_apis

@@ -0,0 +1,8 @@
+audio_out_session
+base
+gems
+libc
+libmpg123
+os
+terminal_session
+vfs

src/app/mp3_audio_sink/component.cc

@@ -0,0 +1,321 @@
+/*
+ * \brief  MP3 audio decoder
+ * \author Emery Hemingway
+ * \date   2018-03-24
+ */
+
+/*
+ * Copyright (C) 2018 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+/*
+ * TODO:
+ * - Metadata report
+ * - Configure the mpg123 volume control and equalizer
+ * - Optimize buffer sizes
+ */
+
+/* Genode includes */
+#include <gems/magic_ring_buffer.h>
+#include <os/static_root.h>
+#include <libc/component.h>
+#include <audio_out_session/connection.h>
+#include <terminal_session/connection.h>
+#include <base/attached_ram_dataspace.h>
+#include <base/sleep.h>
+
+/* Mpg123 includes */
+#include <stdlib.h>
+#include <sys/types.h>
+#include <mpg123.h>
+
+namespace Mp3_audio_sink {
+
+	enum { LEFT, RIGHT, NUM_CHANNELS };
+
+	enum {
+		FEED_POOL_SIZE = 2,
+		CLIENT_BUFFER_SIZE = 1 << 14, /* 16 KiB */
+	};
+
+	enum {
+		AUDIO_OUT_BUFFER_SIZE = NUM_CHANNELS
+			* Audio_out::QUEUE_SIZE
+			* Audio_out::PERIOD
+			* Audio_out::SAMPLE_SIZE
+	};
+
+	using namespace Genode;
+
+	struct Decoder;
+
+	class Terminal_component;
+	struct Main;
+}
+
+
+struct Mp3_audio_sink::Decoder
+{
+	template <typename FUNC>
+	static void for_each_channel(FUNC const &func) {
+		for (int i = 0; i < NUM_CHANNELS; ++i) func(i); }
+
+	Genode::Env &_env;
+
+	Audio_out::Connection _out_left  { _env, "left",  true, true };
+	Audio_out::Connection _out_right { _env, "right", false, false };
+	Audio_out::Connection *_out[NUM_CHANNELS];
+
+	void die_mpg123(mpg123_handle *mh, char const *msg)
+	{
+		int code = mpg123_errcode(mh);
+		Genode::error(msg, ", ", mpg123_strerror(mh));
+
+		mpg123_close(mh);
+		mpg123_delete(mh);
+		mpg123_exit();
+
+		_env.parent().exit(code);
+		Genode::sleep_forever();
+	}
+
+	mpg123_handle *create_mpg123_handle()
+	{
+		mpg123_handle *mh = NULL;
+
+		int err = mpg123_init();
+		if(err != MPG123_OK || (mh = mpg123_new(NULL, &err)) == NULL)
+			Genode::error("Mpg123 setup failed, ", mpg123_plain_strerror(err));
+
+		mpg123_param(mh, MPG123_FEEDPOOL, FEED_POOL_SIZE, 0);
+		mpg123_param(mh, MPG123_FEEDBUFFER, CLIENT_BUFFER_SIZE, 0);
+
+		/* Set mpg123 output format to match Audio_out exactly */
+		mpg123_param(mh, MPG123_FORCE_RATE,
+		             Audio_out::SAMPLE_RATE, Audio_out::SAMPLE_RATE);
+		mpg123_format_none(mh);
+		if (mpg123_format(mh, Audio_out::SAMPLE_RATE,
+		                  MPG123_STEREO, MPG123_ENC_FLOAT_32) != MPG123_OK)
+			die_mpg123(mh, "Audio_out format is unsupported");
+
+		if (mpg123_open_feed(mh) != MPG123_OK)
+			die_mpg123(mh, "mpg123 feeder mode failed");
+		return mh;
+	}
+
+	mpg123_handle *_mh = create_mpg123_handle();
+
+	/* last error code logged */
+	int _mh_err = MPG123_OK;
+
+	/**
+	 * Use half of the available RAM as buffer
+	 */
+	size_t _pcm_buffer_size()
+	{
+		size_t n = _env.pd().avail_ram().value / 2;
+		if (n > (1<<20))
+			log("internal buffer size is ", n>>20, "MiB");
+		else if (n > (1<<10))
+			log("internal buffer size is ", n>>10, "KiB");
+		else
+			log("internal buffer size is ", n, " bytes");
+		return n;
+	}
+
+	Magic_ring_buffer<float> _pcm { _env, _pcm_buffer_size() };
+
+	void _log_error()
+	{
+		int code = mpg123_errcode(_mh);
+		if (code != MPG123_OK && _mh_err != code) {
+			_mh_err = code;
+			error(mpg123_plain_strerror(code));
+		}
+	}
+
+	Genode::size_t feedbuffer_size()
+	{
+		long value = 0;
+		double fvalue = 0;
+		if (mpg123_getparam(_mh, MPG123_FEEDBUFFER, &value, &fvalue))
+			die_mpg123(_mh, "failed to get feed buffer size");
+		return value;
+	}
+
+	void submit_audio();
+
+	/**
+	 * Process client data, blocks until all data is consumed.
+	 */
+	void process(unsigned char const *src, size_t num_bytes)
+	{
+		/* TODO: patch mpgg123 not to use stdio for printing errors */
+
+		Libc::with_libc([&] () {
+
+			/* feed client data into mpg123 buffer */
+			if (mpg123_feed(_mh, src, num_bytes))
+				die_mpg123(_mh, "failed to feed");
+
+			off_t num = 0;
+			unsigned char *audio = nullptr;
+			size_t bytes = 0;
+
+			while (mpg123_decode_frame(_mh, &num, &audio, &bytes) == MPG123_OK) {
+				Genode::size_t const samples = bytes / Audio_out::SAMPLE_SIZE;
+
+				while (_pcm.write_avail() < samples) {
+					/* submit audio blocks for packet allocation */
+					submit_audio();
+				}
+
+				Genode::memcpy(_pcm.write_addr(), audio, bytes);
+				_pcm.fill(samples);
+
+			}
+
+			if (mpg123_errcode(_mh) != MPG123_ERR_READER
+			 || mpg123_errcode(_mh) != MPG123_OK)
+				_log_error();
+		});
+	}
+
+	Io_signal_handler<Decoder> _progress_handler {
+		_env.ep(), *this, &Decoder::submit_audio };
+
+	Decoder(Genode::Env &env) : _env(env)
+	{
+		_out[LEFT]  = &_out_left;
+		_out[RIGHT] = &_out_right;
+		_out_left.progress_sigh(_progress_handler);
+	}
+};
+
+
+void Mp3_audio_sink::Decoder::submit_audio()
+{
+	using namespace Audio_out;
+
+	enum { STEREO_PERIOD = Audio_out::PERIOD*NUM_CHANNELS };
+
+	if (_out_left.stream()->empty()) {
+		for_each_channel([&] (int const c) {
+			_out[c]->start(); });
+		log("Audio_out streams started");
+	}
+
+	while (_pcm.read_avail() > STEREO_PERIOD) {
+		Audio_out::Packet *p[NUM_CHANNELS];
+
+		while (true) {
+			try { p[LEFT] = _out[LEFT]->stream()->alloc(); break; }
+			catch (Audio_out::Stream::Alloc_failed) {
+				_out[LEFT]->wait_for_alloc(); }
+		}
+
+		unsigned const ppos = _out[LEFT]->stream()->packet_position(p[LEFT]);
+		p[RIGHT] = _out[RIGHT]->stream()->get(ppos);
+
+		float const *content = _pcm.read_addr();
+
+		/* copy channel contents into sessions */
+		for (unsigned i = 0; i < STEREO_PERIOD; i += NUM_CHANNELS) {
+			for_each_channel([&] (int const c) {
+				p[c]->content()[i/NUM_CHANNELS] = content[i+c]; });
+		}
+
+		for_each_channel([&] (int const c) {
+			 _out[c]->submit(p[c]); });
+		_pcm.drain(STEREO_PERIOD);
+	}
+
+	if (_out_left.stream()->empty()) {
+		log("Audio_out queue underrun, stopping stream");
+		for_each_channel([&] (int const c) {
+			_out[c]->stop(); });
+	}
+}
+
+
+class Mp3_audio_sink::Terminal_component :
+	public Rpc_object<Terminal::Session, Terminal_component>
+{
+	private:
+
+		Decoder &_decoder;
+
+		Genode::Attached_ram_dataspace _io_buffer;
+
+	public:
+
+		Terminal_component(Genode::Env &env, Decoder &decoder)
+		:
+			_decoder(decoder),
+			_io_buffer(env.pd(), env.rm(), _decoder.feedbuffer_size())
+		{ }
+
+
+		/********************************
+		 ** Terminal session interface **
+		 ********************************/
+
+		Genode::Dataspace_capability _dataspace() {
+			return _io_buffer.cap(); }
+
+		Size size() { return Size(0, 0); }
+
+		bool avail() { return false; }
+
+		Genode::size_t read(void *, Genode::size_t) { return 0; }
+		Genode::size_t _read(Genode::size_t dst_len) { return 0; }
+
+		Genode::size_t write(void const *, Genode::size_t) { return 0; }
+		Genode::size_t _write(Genode::size_t num_bytes)
+		{
+			/* sanitize argument */
+			num_bytes = Genode::min(num_bytes, _io_buffer.size());
+
+			/* copy to decoder */
+			_decoder.process(
+				_io_buffer.local_addr<unsigned char>(), num_bytes);
+
+			return num_bytes;
+		}
+
+		void connected_sigh(Genode::Signal_context_capability cap) {
+			Genode::Signal_transmitter(cap).submit(); }
+
+		void read_avail_sigh(Genode::Signal_context_capability) { }
+
+		void size_changed_sigh(Genode::Signal_context_capability) { }
+};
+
+
+struct Mp3_audio_sink::Main
+{
+	Genode::Env &_env;
+
+	Decoder _decoder { _env };
+
+	Terminal_component _terminal { _env, _decoder };
+
+	Static_root<Terminal::Session> _terminal_root {
+		_env.ep().manage(_terminal) };
+
+	Main(Libc::Env &env) : _env(env)
+	{
+		env.parent().announce(env.ep().manage(_terminal_root));
+	}
+};
+
+
+/***************
+ ** Component **
+ ***************/
+
+void Libc::Component::construct(Libc::Env &env) {
+	static Mp3_audio_sink::Main _main(env); }

src/app/mp3_audio_sink/target.mk

@@ -0,0 +1,5 @@
+TARGET  = mp3_audio_sink
+LIBS   += base libc libm libmpg123
+SRC_CC += component.cc
+
+CC_CXX_WARN_STRICT =

src/app/raw_audio_sink/component.cc

@@ -52,7 +52,17 @@ struct Raw_audio::Sink
 	Audio_out::Connection _out_right { _env, "right", false };
 	Audio_out::Connection *_out[NUM_CHANNELS];
 
-	Magic_ring_buffer<char, AUDIO_OUT_BUFFER_SIZE> _pcm { _env };
+	size_t _buffer_size()
+	{
+		size_t n = AUDIO_OUT_BUFFER_SIZE;
+		enum { RESERVATION = AUDIO_OUT_BUFFER_SIZE+((sizeof(addr_t)*16)<<10) };
+		Ram_quota avail = _env.pd().avail_ram();
+		if (avail.value > RESERVATION)
+			n = avail.value - RESERVATION;
+		return n;
+	}
+
+	Magic_ring_buffer<char> _pcm { _env, _buffer_size() };
 
 	/**
 	 * Process client data, blocks until all data is consumed.