Ramp values to and from a default value while active.

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

@@ -138,16 +138,5 @@ void common_hal_analogio_analogout_set_value(analogio_analogout_obj_t *self,
 }
 
 void analogout_reset(void) {
-    #if defined(SAMD21) && !defined(PIN_PA02)
-    return;
-    #endif
-    #ifdef SAMD21
-    while (DAC->STATUS.reg & DAC_STATUS_SYNCBUSY) {}
-    #endif
-    #ifdef SAMD51
-    while (DAC->SYNCBUSY.reg & DAC_SYNCBUSY_SWRST) {}
-    #endif
-    DAC->CTRLA.reg |= DAC_CTRLA_SWRST;
-
-    // TODO(tannewt): Turn off the DAC clocks to save power.
+    // AudioOut resets the DAC in case its been used for audio which requires special handling.
 }

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

@@ -33,6 +33,7 @@
 #include "py/runtime.h"
 #include "common-hal/audioio/AudioOut.h"
 #include "shared-bindings/audioio/AudioOut.h"
+#include "shared-bindings/microcontroller/__init__.h"
 #include "shared-bindings/microcontroller/Pin.h"
 #include "supervisor/shared/translate.h"
 
@@ -52,11 +53,73 @@
 #include "samd/pins.h"
 #include "samd/timers.h"
 
+#ifdef SAMD21
+static void ramp_value(uint16_t start, uint16_t end) {
+    start = DAC->DATA.reg;
+    int32_t diff = (int32_t) end - start;
+    int32_t step = 49;
+    int32_t steps = diff / step;
+    if (diff < 0) {
+        steps = -steps;
+        step = -step;
+    }
+    for (int32_t i = 0; i < steps; i++) {
+        uint32_t value = start + step * i;
+        DAC->DATA.reg = value;
+        DAC->DATABUF.reg = value;
+        common_hal_mcu_delay_us(50);
+        #ifdef MICROPY_VM_HOOK_LOOP
+            MICROPY_VM_HOOK_LOOP
+        #endif
+    }
+}
+#endif
+
+#ifdef SAMD51
+static void ramp_value(uint16_t start, uint16_t end) {
+    int32_t diff = (int32_t) end - start;
+    int32_t step = 49;
+    int32_t steps = diff / step;
+    if (diff < 0) {
+        steps = -steps;
+        step = -step;
+    }
+
+    for (int32_t i = 0; i < steps; i++) {
+        uint16_t value = start + step * i;
+        DAC->DATA[0].reg = value;
+        DAC->DATABUF[0].reg = value;
+        DAC->DATA[1].reg = value;
+        DAC->DATABUF[1].reg = value;
+
+        common_hal_mcu_delay_us(50);
+        #ifdef MICROPY_VM_HOOK_LOOP
+            MICROPY_VM_HOOK_LOOP
+        #endif
+    }
+}
+#endif
+
 void audioout_reset(void) {
+    #if defined(SAMD21) && !defined(PIN_PA02)
+    return;
+    #endif
+    #ifdef SAMD21
+    while (DAC->STATUS.reg & DAC_STATUS_SYNCBUSY) {}
+    #endif
+    #ifdef SAMD51
+    while (DAC->SYNCBUSY.reg & DAC_SYNCBUSY_SWRST) {}
+    #endif
+    if (DAC->CTRLA.bit.ENABLE) {
+        ramp_value(0x8000, 0);
+    }
+    DAC->CTRLA.reg |= DAC_CTRLA_SWRST;
+
+    // TODO(tannewt): Turn off the DAC clocks to save power.
 }
 
 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) {
+        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
@@ -94,12 +157,10 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
     if (right_channel != NULL) {
         claim_pin(right_channel);
         self->right_channel = right_channel;
-        gpio_set_pin_function(self->right_channel->number, GPIO_PIN_FUNCTION_B);
         audio_dma_init(&self->right_dma);
     }
     #endif
     self->left_channel = left_channel;
-    gpio_set_pin_function(self->left_channel->number, GPIO_PIN_FUNCTION_B);
     audio_dma_init(&self->left_dma);
 
     #ifdef SAMD51
@@ -118,6 +179,10 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
 
     DAC->CTRLA.bit.SWRST = 1;
     while (DAC->CTRLA.bit.SWRST == 1) {}
+    // Make sure there are no outstanding access errors. (Reading DATA can cause this.)
+    #ifdef SAMD51
+    PAC->INTFLAGD.reg = PAC_INTFLAGD_DAC;
+    #endif
 
     bool channel0_enabled = true;
     #ifdef SAMD51
@@ -159,6 +224,8 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
     #endif
     #ifdef SAMD51
     while (DAC->SYNCBUSY.bit.ENABLE == 1) {}
+    while (channel0_enabled && DAC->STATUS.bit.READY0 == 0) {}
+    while (channel1_enabled && DAC->STATUS.bit.READY1 == 0) {}
     #endif
 
     // Use a timer to coordinate when DAC conversions occur.
@@ -220,13 +287,21 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
 
     #ifdef SAMD51
     connect_event_user_to_channel(EVSYS_ID_USER_DAC_START_1, channel);
+    if (right_channel != NULL) {
+        gpio_set_pin_function(self->right_channel->number, GPIO_PIN_FUNCTION_B);
+    }
     #define EVSYS_ID_USER_DAC_START EVSYS_ID_USER_DAC_START_0
     #endif
     connect_event_user_to_channel(EVSYS_ID_USER_DAC_START, channel);
+    gpio_set_pin_function(self->left_channel->number, GPIO_PIN_FUNCTION_B);
     init_async_event_channel(channel, tc_gen_id);
 
     self->tc_to_dac_event_channel = channel;
 
+    // Ramp the DAC up.
+    self->quiescent_value = quiescent_value;
+    ramp_value(0, quiescent_value);
+
     // Leave the DMA setup to playback.
 }
 
@@ -239,6 +314,9 @@ void common_hal_audioio_audioout_deinit(audioio_audioout_obj_t* self) {
         return;
     }
 
+    // Ramp the DAC down.
+    ramp_value(self->quiescent_value, 0);
+
     DAC->CTRLA.bit.ENABLE = 0;
     #ifdef SAMD21
     while (DAC->STATUS.bit.SYNCBUSY == 1) {}
@@ -381,6 +459,9 @@ void common_hal_audioio_audioout_stop(audioio_audioout_obj_t* self) {
     #ifdef SAMD51
     audio_dma_stop(&self->right_dma);
     #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->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

@@ -44,6 +44,7 @@ typedef struct {
 
     uint8_t tc_to_dac_event_channel;
     bool playing;
+    uint16_t quiescent_value;
 } audioio_audioout_obj_t;
 
 void audioout_reset(void);

ports/atmel-samd/supervisor/port.c

@@ -249,11 +249,11 @@ void reset_port(void) {
     }
 
 #if defined(EXPRESS_BOARD) && !defined(__SAMR21G18A__)
+    audio_dma_reset();
     audioout_reset();
     #if !defined(__SAMD51G19A__) && !defined(__SAMD51G18A__)
     i2sout_reset();
     #endif
-    audio_dma_reset();
     //pdmin_reset();
 #endif
 #ifdef SAMD21

shared-bindings/audioio/AudioOut.c

@@ -43,13 +43,15 @@
 //|
 //| AudioOut can be used to output an analog audio signal on a given pin.
 //|
-//| .. class:: AudioOut(left_channel, right_channel=None)
+//| .. 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 quiescent_value: The output value when no signal is present. Samples should start
+//|       and end with this value to prevent audible popping.
 //|
 //|   Simple 8ksps 440 Hz sin wave::
 //|
@@ -95,10 +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 };
+    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_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);
@@ -117,7 +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);
+    common_hal_audioio_audioout_construct(self, left_channel_pin, right_channel_pin, args[ARG_quiescent_value].u_int);
 
     return MP_OBJ_FROM_PTR(self);
 }

shared-bindings/audioio/AudioOut.h

@@ -35,7 +35,7 @@ extern const mp_obj_type_t audioio_audioout_type;
 
 // left_channel will always be non-NULL but right_channel may be for mono output.
 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);
+    const mcu_pin_obj_t* left_channel, const mcu_pin_obj_t* right_channel, uint16_t default_value);
 
 void common_hal_audioio_audioout_deinit(audioio_audioout_obj_t* self);
 bool common_hal_audioio_audioout_deinited(audioio_audioout_obj_t* self);