Implement setting square wave duty cycle

2 files changed, 13 insertions, 2 deletions

diff --git a/include/xas/synth.h b/include/xas/synth.h
index ca83c69..cb0b3bd 100644
--- a/include/xas/synth.h
+++ b/include/xas/synth.h
@@ -8,6 +8,7 @@
 #include <xas/audio.h>
 
 #define XAS_SYNTH_DEFAULT_GAIN      1.0f
+#define XAS_SYNTH_DEFAULT_DUTY      1.0f
 #define XAS_SYNTH_DEFAULT_FREQUENCY 2600 /* Hz */
 
 enum xas_synth_type {
@@ -38,7 +39,8 @@ struct _xas_synth {
     xas_synth_sample_callback sample;
 
     float phase,
-          gain;
+          gain,
+          duty;
 
     size_t frequency;
 };
@@ -51,6 +53,8 @@ void xas_synth_destroy(xas_synth *synth);
 
 void xas_synth_set_gain(xas_synth *synth, float gain);
 
+void xas_synth_set_duty(xas_synth *synth, float duty);
+
 void xas_synth_set_frequency(xas_synth *synth, size_t frequency);
 
 void xas_synth_set_type(xas_synth *synth, enum xas_synth_type type);
diff --git a/src/synth.c b/src/synth.c
index b01ebc8..0be572d 100644
--- a/src/synth.c
+++ b/src/synth.c
@@ -27,8 +27,10 @@ static int16_t sample_square(xas_synth *synth) {
     int16_t ret;
     static float tau = 2.0f * M_PI;
 
+    float duty = synth->duty;
+
     if (synth->state == XAS_SYNTH_ACTIVE) {
-        ret = (synth->phase - M_PI) > 0.0?
+        ret = ((duty * synth->phase) - M_PI) > 0.0?
             (int16_t)roundf(synth->gain * (INT16_MAX / 4)):
             (int16_t)roundf(synth->gain * (INT16_MIN / 4));
 
@@ -156,6 +158,7 @@ xas_synth *xas_synth_new(xas_audio_format format,
     synth->state     = XAS_SYNTH_IDLE;
     synth->phase     = 0.0f;
     synth->gain      = XAS_SYNTH_DEFAULT_GAIN;
+    synth->duty      = XAS_SYNTH_DEFAULT_DUTY;
     synth->frequency = XAS_SYNTH_DEFAULT_FREQUENCY;
 
     synth->format.channels    = XAS_AUDIO_MONO;
@@ -184,6 +187,10 @@ void xas_synth_set_gain(xas_synth *synth, float gain) {
     synth->gain = gain;
 }
 
+void xas_synth_set_duty(xas_synth *synth, float duty) {
+    synth->duty = duty;
+}
+
 void xas_synth_set_type(xas_synth *synth, enum xas_synth_type type) {
     set_type(synth, type);
 }