Reduce popping during audio initialization using the additive DAC (#21642)

platforms/chibios/drivers/audio_dac_additive.c

@@ -84,7 +84,7 @@ static const dacsample_t dac_buffer_trapezoid[AUDIO_DAC_BUFFER_SIZE] = {0x0,   0
                                                                         0xfff, 0xfdf, 0xf7f, 0xf1f, 0xebf, 0xe5f, 0xdff, 0xd9f, 0xd3f, 0xcdf, 0xc7f, 0xc1f, 0xbbf, 0xb5f, 0xaff, 0xa9f, 0xa3f, 0x9df, 0x97f, 0x91f, 0x8bf, 0x85f, 0x7ff, 0x79f, 0x73f, 0x6df, 0x67f, 0x61f, 0x5bf, 0x55f, 0x4ff, 0x49f, 0x43f, 0x3df, 0x37f, 0x31f, 0x2bf, 0x25f, 0x1ff, 0x19f, 0x13f, 0xdf,  0x7f,  0x1f,  0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0,   0x0};
 #endif // AUDIO_DAC_SAMPLE_WAVEFORM_TRAPEZOID
 
-static dacsample_t dac_buffer_empty[AUDIO_DAC_BUFFER_SIZE] = {AUDIO_DAC_OFF_VALUE};
+static dacsample_t dac_buffer[AUDIO_DAC_BUFFER_SIZE];
 
 /* keep track of the sample position for for each frequency */
 static float dac_if[AUDIO_MAX_SIMULTANEOUS_TONES] = {0.0};
@@ -311,10 +311,17 @@ void audio_driver_initialize(void) {
     DACD1.params->dac->CR &= ~DAC_CR_BOFF1;
     DACD2.params->dac->CR &= ~DAC_CR_BOFF2;
 
+    /* Start the DAC output with all off values. This buffer will then get fed
+     * with samples from dac_end, which will play notes.
+     */
+    for (size_t i = 0; i < AUDIO_DAC_BUFFER_SIZE; i++) {
+        dac_buffer[i] = AUDIO_DAC_OFF_VALUE;
+    }
+
     if (AUDIO_PIN == A4) {
-        dacStartConversion(&DACD1, &dac_conv_cfg, dac_buffer_empty, AUDIO_DAC_BUFFER_SIZE);
+        dacStartConversion(&DACD1, &dac_conv_cfg, dac_buffer, AUDIO_DAC_BUFFER_SIZE);
     } else if (AUDIO_PIN == A5) {
-        dacStartConversion(&DACD2, &dac_conv_cfg, dac_buffer_empty, AUDIO_DAC_BUFFER_SIZE);
+        dacStartConversion(&DACD2, &dac_conv_cfg, dac_buffer, AUDIO_DAC_BUFFER_SIZE);
     }
 
     // no inverted/out-of-phase waveform (yet?), only pulling AUDIO_PIN_ALT to AUDIO_DAC_OFF_VALUE