add pll

lib/filters.c

@@ -12,4 +12,39 @@ float apply_preemphasis(ResistorCapacitor *filter, float sample) {
 
 float hard_clip(float sample, float threshold) {
     return fmaxf(-threshold, fminf(threshold, sample));
+}
+
+void init_pll(PLL *pll, float output_freq, float reference_freq, float loop_filter_bandwidth, int quadrature_mode, int sample_rate) {
+    pll->phase = 0.0f;
+    pll->freq = output_freq;
+    pll->ref_freq = reference_freq;
+    pll->loop_filter_state = 0.0f;
+    
+    float damping = 0.707;
+    pll->kp = 2.0f * damping * loop_filter_bandwidth;
+    pll->ki = loop_filter_bandwidth * loop_filter_bandwidth;
+    
+    pll->sample_rate = sample_rate;
+    pll->quadrature_mode = quadrature_mode;
+}
+
+float apply_pll(PLL *pll, float ref_sample, float input_sample) {
+    float phase_error;
+    if (pll->quadrature_mode) {
+        phase_error = ref_sample * sinf(pll->phase) - input_sample * cosf(pll->phase);
+    } else {
+        phase_error = ref_sample * input_sample * sinf(pll->phase);
+    }
+    
+    float filter_output = pll->kp * phase_error + pll->loop_filter_state;
+    pll->loop_filter_state += pll->ki * phase_error * (1/pll->sample_rate);
+    
+    pll->freq = pll->freq + filter_output;
+    
+    pll->phase += M_2PI * pll->freq * (1.0f/pll->sample_rate);
+    if (pll->phase > M_2PI) {
+        pll->phase -= M_2PI;
+    }
+    
+    return cosf(pll->phase);
 }

lib/filters.h

@@ -14,4 +14,17 @@ typedef struct
 void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate);
 float apply_preemphasis(ResistorCapacitor *filter, float sample);
 
-float hard_clip(float sample, float threshold);
+float hard_clip(float sample, float threshold);
+
+typedef struct {
+    float phase;
+    float freq;
+    float ref_freq;
+    float loop_filter_state;
+    float kp;
+    float ki;
+    int sample_rate;
+    int quadrature_mode;
+} PLL;
+void init_pll(PLL *pll, float output_freq, float refrence_freq, float loop_filter_bandwidth, int quadrature_mode, int sample_rate);
+float apply_pll(PLL *pll, float ref_sample, float input_sample);