Add README, add license statement.

README

@@ -0,0 +1,81 @@
+
+  SoftFM - Software decoder for FM broadcast radio with RTL-SDR
+ ---------------------------------------------------------------
+
+SoftFM is a software-defined radio receiver for FM broadcast radio.
+It is written in C++ and uses RTL-SDR to interface with RTL2832-based
+hardware.
+
+This program is mostly an experiment rather than a useful tool.
+The purposes of SoftFM are
+ * experimenting with digital signal processing and software radio;
+ * investigating the stability of the 19 kHz pilot;
+ * doing the above while listening to my favorite radio station.
+
+Having said that, SoftFM actually produces pretty good stereo sound
+when receiving a strong radio station.  Weak stations are noisy,
+but SoftFM gets much better results than rtl_fm (bundled with RTL-SDR)
+and the few GNURadio-based FM receivers I have seen.
+
+SoftFM provides:
+ * mono or stereo decoding of FM broadcasting stations
+ * real-time playback to soundcard or dumping to file
+ * command-line interface (no GUI, no visualization, nothing fancy)
+
+SoftFM requires:
+ * Linux
+ * C++11
+ * RTL-SDR library (http://sdr.osmocom.org/trac/wiki/rtl-sdr)
+ * supported DVB-T receiver
+ * medium-fast computer (SoftFM takes 25% CPU time on my 1.6 GHz Core i3)
+ * medium-strong FM radio signal
+
+For the latest version, see https://github.com/jorisvr/SoftFM
+
+
+  Installing
+  ----------
+
+The Osmocom RTL-SDR library must be installed before you can build SoftFM.
+See http://sdr.osmocom.org/trac/wiki/rtl-sdr for more information.
+
+To install SoftFM, download and unpack the source code and go to the
+top level directory. Then do like this:
+
+ $ mkdir build
+ $ cd build
+ $ cmake ..
+
+ # CMake tries to find librtlsdr. If this fails, you need to specify
+ # the location of the library in one the following ways:
+ #
+ #  $ cmake .. -DCMAKE_INSTALL_PREFIX=/path/rtlsdr
+ #  $ cmake .. -DRTLSDR_INCLUDE_DIR=/path/rtlsdr/include -DRTLSDR_LIBRARY_PATH=/path/rtlsdr/lib/librtlsdr.a
+ #  $ PKG_CONFIG_PATH=/path/rtlsdr/lib/pkgconfig cmake ..
+
+ $ make
+
+ $ ./softfm -f <radio-frequency-in-Hz>
+
+ # ( enjoy music )
+
+
+  License
+  -------
+
+SoftFM, copyright (C) 2013, Joris van Rantwijk
+
+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/gpl-2.0.html
+
+--

TODO.txt

@@ -1,9 +1,9 @@
-* write README.txt
 * push to github
 * implement WAV file writing
 * implement stereo pilot PPS
 * implement RDS decoding
 * figure out why we sometimes lose stereo lock
+* it looks like IF level sometimes varies so much that it saturates the receiver; perhaps this can be solved by dynamically managing the hardware gain in response to level measurements
 * investigate problem at low IF sample rates; apparently librtlsdr is not telling the truth about the actual sample rate.
 * look at I/Q balance to improve weak stations
 * look at hardware gain settings to improve weak stations

main.cc

@@ -1,7 +1,20 @@
 /*
  *  SoftFM - Software decoder for FM broadcast radio with RTL-SDR
  *
- *  Joris van Rantwijk, 2013.
+ *  Copyright (C) 2013, Joris van Rantwijk.
+ *
+ *  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/gpl-2.0.html
  */
 
 #include <cstdlib>