Tweaks from feedback:

* default_value is now quiescent_value
* Use step = -step format for sign switch
* Add note about analogout_reset being empty

ports/atmel-samd/common-hal/analogio/AnalogOut.c

@@ -138,4 +138,5 @@ void common_hal_analogio_analogout_set_value(analogio_analogout_obj_t *self,
 }
 
 void analogout_reset(void) {
+    // AudioOut resets the DAC in case its been used for audio which requires special handling.
 }

ports/atmel-samd/common-hal/audioio/AudioOut.c

@@ -60,8 +60,8 @@ static void ramp_value(uint16_t start, uint16_t end) {
     int32_t step = 49;
     int32_t steps = diff / step;
     if (diff < 0) {
-        steps *= -1;
+        steps = -steps;
-        step *= -1;
+        step = -step;
     }
     for (int32_t i = 0; i < steps; i++) {
         uint32_t value = start + step * i;
@@ -81,8 +81,8 @@ static void ramp_value(uint16_t start, uint16_t end) {
     int32_t step = 49;
     int32_t steps = diff / step;
     if (diff < 0) {
-        steps *= -1;
+        steps = -steps;
-        step *= -1;
+        step = -step;
     }
 
     for (int32_t i = 0; i < steps; i++) {
@@ -119,7 +119,7 @@ void audioout_reset(void) {
 }
 
 void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
-        const mcu_pin_obj_t* left_channel, const mcu_pin_obj_t* right_channel, uint16_t default_value) {
+        const mcu_pin_obj_t* left_channel, const mcu_pin_obj_t* right_channel, uint16_t quiescent_value) {
     #ifdef SAMD51
     bool dac_clock_enabled = hri_mclk_get_APBDMASK_DAC_bit(MCLK);
     #endif
@@ -299,8 +299,8 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
     self->tc_to_dac_event_channel = channel;
 
     // Ramp the DAC up.
-    self->default_value = default_value;
+    self->quiescent_value = quiescent_value;
-    ramp_value(0, default_value);
+    ramp_value(0, quiescent_value);
 
     // Leave the DMA setup to playback.
 }
@@ -315,7 +315,7 @@ void common_hal_audioio_audioout_deinit(audioio_audioout_obj_t* self) {
     }
 
     // Ramp the DAC down.
-    ramp_value(self->default_value, 0);
+    ramp_value(self->quiescent_value, 0);
 
     DAC->CTRLA.bit.ENABLE = 0;
     #ifdef SAMD21
@@ -461,7 +461,7 @@ void common_hal_audioio_audioout_stop(audioio_audioout_obj_t* self) {
     #endif
     // Ramp the DAC to default. The start is ignored when the current value can be readback.
     // Otherwise, we just set it immediately.
-    ramp_value(self->default_value, self->default_value);
+    ramp_value(self->quiescent_value, self->quiescent_value);
 }
 
 bool common_hal_audioio_audioout_get_playing(audioio_audioout_obj_t* self) {

ports/atmel-samd/common-hal/audioio/AudioOut.h

@@ -44,7 +44,7 @@ typedef struct {
 
     uint8_t tc_to_dac_event_channel;
     bool playing;
-    uint16_t default_value;
+    uint16_t quiescent_value;
 } audioio_audioout_obj_t;
 
 void audioout_reset(void);

shared-bindings/audioio/AudioOut.c

@@ -43,15 +43,15 @@
 //|
 //| AudioOut can be used to output an analog audio signal on a given pin.
 //|
-//| .. class:: AudioOut(left_channel, *, right_channel=None, default_value=0x8000)
+//| .. class:: AudioOut(left_channel, *, right_channel=None, quiescent_value=0x8000)
 //|
 //|   Create a AudioOut object associated with the given pin(s). This allows you to
 //|   play audio signals out on the given pin(s).
 //|
 //|   :param ~microcontroller.Pin left_channel: The pin to output the left channel to
 //|   :param ~microcontroller.Pin right_channel: The pin to output the right channel to
-//|   :param int default_value: The default output value. Samples should start and end with this
+//|   :param int quiescent_value: The output value when no signal is present. Samples should start
-//|       value to prevent popping.
+//|       and end with this value to prevent audible popping.
 //|
 //|   Simple 8ksps 440 Hz sin wave::
 //|
@@ -97,11 +97,11 @@ STATIC mp_obj_t audioio_audioout_make_new(const mp_obj_type_t *type, size_t n_ar
     mp_arg_check_num(n_args, n_kw, 1, 2, true);
     mp_map_t kw_args;
     mp_map_init_fixed_table(&kw_args, n_kw, pos_args + n_args);
-    enum { ARG_left_channel, ARG_right_channel, ARG_default_value };
+    enum { ARG_left_channel, ARG_right_channel, ARG_quiescent_value };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_left_channel, MP_ARG_OBJ | MP_ARG_REQUIRED },
         { MP_QSTR_right_channel, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_rom_obj = mp_const_none} },
-        { MP_QSTR_default_value, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_int = 0x8000} },
+        { MP_QSTR_quiescent_value, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_int = 0x8000} },
     };
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all(n_args, pos_args, &kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
@@ -120,7 +120,7 @@ STATIC mp_obj_t audioio_audioout_make_new(const mp_obj_type_t *type, size_t n_ar
     // create AudioOut object from the given pin
     audioio_audioout_obj_t *self = m_new_obj(audioio_audioout_obj_t);
     self->base.type = &audioio_audioout_type;
-    common_hal_audioio_audioout_construct(self, left_channel_pin, right_channel_pin, args[ARG_default_value].u_int);
+    common_hal_audioio_audioout_construct(self, left_channel_pin, right_channel_pin, args[ARG_quiescent_value].u_int);
 
     return MP_OBJ_FROM_PTR(self);
 }