Switch to direct use of librtlsdr and PulseAudio

Substantial rework to replace the spawning of rtl_fm and aplay with direct
usage of librtlsdr and PulseAudio in a multi-threaded model. This is required
due to changes in AGL application execution that prevent spawned processes from
exiting, resulting in the plugin hanging on frequency changes or stopping.

The rework has been accomplished by refactoring the source of rtl_fm.c into a
reusable form and connecting it to the RtlFmRadioTunerControl class used to
implement the functionality exposed by the RtlFmRadioPlugin class. The idea for
reusing the source code in rtl_fm.c in this way is inspired by the older
qml_radio_plugin codebase, but a new refactor of rtl_fm.c was done to keep more
of its filtering functionality and ensure behavior consistent with the previous
implementation. The files radio_output.{h,cpp} are adapted from qml_radio_plugin
with some additional modifications.

Other changes include:
- The files in the convenience subdirectory have been copied from the librtldr
  source tree to reduce the effort of importing rtl_fm.c.
- The COPYING file containing the GPL license has been copied from the
  librtlsdr source tree to accompany rtl_fm.c and the convenience/* files.
- The recently added AM band support has been removed as the USB DVB adapters
  are incapable of receiving AM without significant tweaking, and a single
  adapter would be unable to do both AM and FM at the same time. The plugin
  now explicitly reports that it only supports FM.
- The list of known stations to act as an ersatz seeking implementation has
  been removed, as the updated higher-level QML application no longer exposes
  seeking. Adding this functionality back in would be straightforward if it
  becomes required again. There is also some code in rtl_fm.c that could possibly
  be adapted into a proper signal strength detection scheme in the future if
  that is desired.
- A Qt QSettings file is used to store the FM band plan information to
  allow using the specific frequency ranges for North America versus Japan.
  The band plan can be changed by modifying the "fmbandplan" entry in the
  QSettings .conf file to either "US" or "JP". The location of the .conf file
  can be one of:

  $HOME/.config/AGL/qtmultimedia-rtlfm-radio-plugin.conf
  $HOME/.config/AGL.conf
  /etc/xdg/AGL/qtmultimedia-rtlfm-radio-plugin.conf
  /etc/xdg/AGL.conf

Note that some debugging output has been left in place in the start and stop
methods to facilitate debugging of the higher-level QML application.  They will
be removed once that is complete.

Change-Id: I1d92c74eb24b24cb5416dd531b599645d1287295
Signed-off-by: Scott Murray <scott.murray@konsulko.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/rtl_fm.h b/rtl_fm.h
new file mode 100644
index 0000000..a35d341
--- /dev/null
+++ b/rtl_fm.h
@@ -0,0 +1,50 @@
+/*
+ * rtl-sdr, turns your Realtek RTL2832 based DVB dongle into a SDR receiver
+ * Copyright (C) 2016 by Scott Murray <scott.murray@konsulko.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef RTL_FM_H
+#define RTL_FM_H
+
+#define RTL_FM_DEFAULT_BUF_LENGTH	(1 * 16384)
+#define RTL_FM_MAXIMUM_OVERSAMPLE	16
+#define RTL_FM_MAXIMUM_BUF_LENGTH	(RTL_FM_MAXIMUM_OVERSAMPLE * RTL_FM_DEFAULT_BUF_LENGTH)
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef void (*rtl_fm_output_fn_t)(int16_t *result, int result_len, void *data);
+
+int rtl_fm_init(uint32_t freq,
+		uint32_t sample_rate,
+		uint32_t resample_rate,
+		rtl_fm_output_fn_t output_fn,
+		void *output_fn_data);
+
+void rtl_fm_start(void);
+
+void rtl_fm_set_freq(uint32_t freq);
+
+void rtl_fm_stop(void);
+
+void rtl_fm_cleanup(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* RTL_FM_H */