From 762a3ea78896a0ea654e65d6543e6708daabb37f Mon Sep 17 00:00:00 2001
From: Kamal Mostafa <kamal@whence.com>
Date: Sat, 25 Aug 2012 00:32:11 -0700
Subject: [PATCH] minimodem: --volume sets tx amplitude

---
 src/minimodem.1.in          |  5 +++++
 src/minimodem.c             | 19 +++++++++++++++----
 src/simple-tone-generator.c | 19 ++++++++++++++-----
 src/simpleaudio.h           |  2 +-
 4 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/src/minimodem.1.in b/src/minimodem.1.in
index cb49296..b4936dc 100644
--- a/src/minimodem.1.in
+++ b/src/minimodem.1.in
@@ -73,6 +73,11 @@ encode or decode an audio file (extension sets audio format)
 .TP
 .B \-b, \-\-bandwidth {rx_bandwidth}
 .TP
+.B \-v, \-\-volume {tx_amplitude or 'E'}
+Sets the generated signal amplitude (default is 1.0).  As a special case
+useful for testing, the value 'E' sets the amplitude to the very small value
+FLT_EPSILON.  (This option applies to \-\-tx mode only).
+.TP
 .B \-M, \-\-mark {mark_freq}
 .TP
 .B \-S, \-\-space {space_freq}
diff --git a/src/minimodem.c b/src/minimodem.c
index 33b7656..4573330 100644
--- a/src/minimodem.c
+++ b/src/minimodem.c
@@ -26,6 +26,7 @@
 #include <string.h>
 #include <ctype.h>
 #include <math.h>
+#include <float.h>
 #include <assert.h>
 #include <signal.h>
 #include <sys/time.h>
@@ -257,7 +258,7 @@ benchmarks()
 
 
     // enable the sine wave LUT
-    simpleaudio_tone_init(1024);
+    simpleaudio_tone_init(1024, 1.0);
 
     sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
 			SA_SAMPLE_FORMAT_S16, sample_rate, 1,
@@ -277,7 +278,7 @@ benchmarks()
 
 
     // disable the sine wave LUT
-    simpleaudio_tone_init(0);
+    simpleaudio_tone_init(0, 1.0);
 
     sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
 			SA_SAMPLE_FORMAT_S16, sample_rate, 1,
@@ -328,6 +329,7 @@ usage()
     "		    -5, --baudot	Baudot 5-N-1\n"
     "		    -f, --file {filename.flac}\n"
     "		    -b, --bandwidth {rx_bandwidth}\n"
+    "		    -v, --volume {amplitude or 'E'}\n"
     "		    -M, --mark {mark_freq}\n"
     "		    -S, --space {space_freq}\n"
     "		    -T, --txstopbits {m.n}\n"
@@ -382,6 +384,7 @@ main( int argc, char*argv[] )
     unsigned int sample_rate = 48000;
     unsigned int nchannels = 1; // FIXME: only works with one channel
 
+    float tx_amplitude = 1.0;
     unsigned int tx_sin_table_len = 4096;
 
     /* validate the default system audio mechanism */
@@ -424,6 +427,7 @@ main( int argc, char*argv[] )
 	    { "baudot",		0, 0, '5' },
 	    { "file",		1, 0, 'f' },
 	    { "bandwidth",	1, 0, 'b' },
+	    { "volume",		1, 0, 'v' },
 	    { "mark",		1, 0, 'M' },
 	    { "space",		1, 0, 'S' },
 	    { "txstopbits",	1, 0, 'T' },
@@ -435,7 +439,7 @@ main( int argc, char*argv[] )
 	    { "benchmarks",	0, 0, MINIMODEM_OPT_BENCHMARKS },
 	    { 0 }
 	};
-	c = getopt_long(argc, argv, "Vtrc:l:a85f:b:M:S:T:qAR:",
+	c = getopt_long(argc, argv, "Vtrc:l:a85f:b:v:M:S:T:qAR:",
 		long_options, &option_index);
 	if ( c == -1 )
 	    break;
@@ -475,6 +479,13 @@ main( int argc, char*argv[] )
 			band_width = atof(optarg);
 			assert( band_width != 0 );
 			break;
+	    case 'v':
+			if ( optarg[0] == 'E' )
+			    tx_amplitude = FLT_EPSILON;
+			else
+			    tx_amplitude = atof(optarg);
+			assert( tx_amplitude > 0.0 );
+			break;
 	    case 'M':
 			bfsk_mark_f = atoi(optarg);
 			assert( bfsk_mark_f > 0 );
@@ -642,7 +653,7 @@ main( int argc, char*argv[] )
      */
     if ( TX_mode ) {
 
-	simpleaudio_tone_init(tx_sin_table_len);
+	simpleaudio_tone_init(tx_sin_table_len, tx_amplitude);
 
 	int tx_interactive = 0;
 	if ( ! stream_name ) {
diff --git a/src/simple-tone-generator.c b/src/simple-tone-generator.c
index 4ca88a5..bc459f3 100644
--- a/src/simple-tone-generator.c
+++ b/src/simple-tone-generator.c
@@ -27,14 +27,17 @@
 
 
 
+static float tone_mag = 1.0;
+
 static unsigned int sin_table_len;
 static short *sin_table_short;
 static float *sin_table_float;
 
 void
-simpleaudio_tone_init( unsigned int new_sin_table_len )
+simpleaudio_tone_init( unsigned int new_sin_table_len, float mag )
 {
     sin_table_len = new_sin_table_len;
+    tone_mag = mag;
 
     if ( sin_table_len != 0 ) {
 	sin_table_short = realloc(sin_table_short, sin_table_len * sizeof(short));
@@ -45,10 +48,13 @@ simpleaudio_tone_init( unsigned int new_sin_table_len )
 	}
 
 	unsigned int i;
+	unsigned short mag_s = 32767.0 * tone_mag + 0.5f;
+	if ( mag_s < 2 ) // "short epsilon"
+	    mag_s = 2;
 	for ( i=0; i<sin_table_len; i++ )
-	    sin_table_short[i] = 32767 * sin(M_PI*2.0*(float)i/sin_table_len);
+	    sin_table_short[i] = mag_s * sin(M_PI*2.0*(float)i/sin_table_len);
 	for ( i=0; i<sin_table_len; i++ )
-	    sin_table_float[i] = sinf(M_PI*2.0*(float)i/sin_table_len);
+	    sin_table_float[i] = tone_mag * sinf(M_PI*2.0*(float)i/sin_table_len);
 
     } else {
 	if ( sin_table_short ) {
@@ -122,7 +128,7 @@ simpleaudio_tone(simpleaudio *sa_out, float tone_freq, size_t nsamples_dur)
 			    float_buf[i] = sin_lu_float(SINE_PHASE_TURNS);
 		    } else {
 			for ( i=0; i<nsamples_dur; i++ )
-			    float_buf[i] = sinf(SINE_PHASE_RADIANS);
+			    float_buf[i] = tone_mag * sinf(SINE_PHASE_RADIANS);
 		    }
 		}
 		break;
@@ -134,8 +140,11 @@ simpleaudio_tone(simpleaudio *sa_out, float tone_freq, size_t nsamples_dur)
 			for ( i=0; i<nsamples_dur; i++ )
 			    short_buf[i] = sin_lu_short(SINE_PHASE_TURNS);
 		    } else {
+			unsigned short mag_s = 32767.0 * tone_mag + 0.5f;
+			if ( mag_s < 2 ) // "short epsilon"
+			    mag_s = 2;
 			for ( i=0; i<nsamples_dur; i++ )
-			    short_buf[i] = 32767 * sinf(SINE_PHASE_RADIANS);
+			    short_buf[i] = mag_s * sinf(SINE_PHASE_RADIANS);
 		    }
 		    break;
 		}
diff --git a/src/simpleaudio.h b/src/simpleaudio.h
index b9c689c..537a1e9 100644
--- a/src/simpleaudio.h
+++ b/src/simpleaudio.h
@@ -96,6 +96,6 @@ void
 simpleaudio_tone(simpleaudio *sa_out, float tone_freq, size_t nsamples_dur);
 
 void
-simpleaudio_tone_init( unsigned int new_sin_table_len );
+simpleaudio_tone_init( unsigned int new_sin_table_len, float mag );
 
 #endif