Improved audio beep tone (#2014)

* Improved sine wave beep tone

* Prevent divide-by-zero

firmware/baseband/audio_dma.cpp

@@ -239,19 +239,41 @@ void shrink_tx_buffer(bool shrink) {
 }
 
 void beep_start(uint32_t freq, uint32_t sample_rate, uint32_t beep_duration_ms) {
-    tone_gen.configure_beep(freq, sample_rate);
+    // Prevent divide-by-0
+    if (freq == 0 || sample_rate == 0)
+        return;
 
+    // Fill entire buffer with sine waves
+    tone_gen.configure_beep(freq, sample_rate);
     for (size_t i = 0; i < buffer_samples; i++)
         buffer_tx[i].left = buffer_tx[i].right = tone_gen.process_beep();
 
-    uint32_t beep_interrupt_count = beep_duration_ms * sample_rate / (1000 * transfer_samples);
+    // Try to adjust DMA transfer count to align with full sine waves for a better tone
+    float samples_per_sine_wave = float(sample_rate) / freq;
+    uint32_t sine_waves_per_buffer = buffer_samples / samples_per_sine_wave;
+    size_t sample_count = (sine_waves_per_buffer == 0) ? buffer_samples : sine_waves_per_buffer * samples_per_sine_wave + 0.5;
+
+    // Use single larger transfer buffer with sample count determined above
+    lli_tx_loop[0].lli = lli_pointer(&lli_tx_loop[0]);
+    lli_tx_loop[0].control = control_tx(sample_count * sizeof(sample_t));
+
+    // Convert duration ms to number of buffers to send before stopping
+    // NB: beep_duration_ms==0 means beep continuously until stopped
+    uint32_t beep_interrupt_count = beep_duration_ms * sample_rate / (1000 * sample_count);
     if ((beep_duration_ms != 0) && (beep_interrupt_count == 0))
         beep_interrupt_count = 1;
     beep_duration_downcounter = beep_interrupt_count;
 }
 
 void beep_stop() {
+    // Clear audio DMA buffer
     memset(&buffer_tx, 0, buffer_bytes);
+
+    // Restore DMA linked list to use multiple smaller buffers
+    lli_tx_loop[0].control = control_tx(transfer_bytes);
+    if (!single_tx_buffer && (transfers_per_buffer > 1)) {
+        lli_tx_loop[0].lli = lli_pointer(&lli_tx_loop[1]);
+    }
 }
 
 buffer_t tx_empty_buffer() {

firmware/baseband/tone_gen.cpp

@@ -27,6 +27,7 @@
 // Functions for audio beep (used by Sonde RSSI)
 void ToneGen::configure_beep(const uint32_t freq, const uint32_t sample_rate) {
     f_delta_ = (float)(freq * sizeof(sine_table_i8)) / sample_rate;
+    f_tone_phase_ = 0.0;
 }
 
 int16_t ToneGen::process_beep() {
@@ -44,6 +45,7 @@ int16_t ToneGen::process_beep() {
 
 void ToneGen::configure(const uint32_t delta, const float tone_mix_weight) {
     delta_ = delta;
+    tone_phase_ = 0;
     tone_mix_weight_ = tone_mix_weight;
     input_mix_weight_ = 1.0 - tone_mix_weight;
 }