Tweaks based on dhalbert's feedback.

ports/atmel-samd/Makefile

@@ -364,15 +364,12 @@ SRC_COMMON_HAL += \
 	audiobusio/__init__.c \
 	audiobusio/I2SOut.c
 endif
-ifeq ($(CHIP_VARIANT),SAMD51G18)
-SRC_COMMON_HAL += \
-	audiobusio/__init__.c \
-	audiobusio/I2SOut.c
-endif
-ifeq ($(CHIP_VARIANT),SAMD51G19)
-SRC_COMMON_HAL += \
-	audiobusio/__init__.c \
-	audiobusio/I2SOut.c
+ifneq ($(CHIP_VARIANT),SAMD51G18A)
+	ifneq ($(CHIP_VARIANT),SAMD51G19A)
+		SRC_COMMON_HAL += \
+			audiobusio/__init__.c \
+			audiobusio/I2SOut.c
+	endif
 endif
 
 SRC_SHARED_MODULE_EXPANDED = $(addprefix shared-bindings/, $(SRC_SHARED_MODULE)) \

ports/atmel-samd/clocks.c

@@ -35,7 +35,7 @@
 // TODO(tannewt): Should we have a way of sharing GCLKs based on their speed? Divisor doesn't
 // gaurantee speed because it depends on the source.
 uint8_t find_free_gclk(uint16_t divisor) {
-    if (divisor > (1 << 8)) {
+    if (divisor > 0xff) {
         if (gclk_enabled(1)) {
             return 0xff;
         }

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

@@ -51,11 +51,21 @@
 #include "timers.h"
 
 void audioout_reset(void) {
-    // Only reset DMA. PWMOut will reset the timer. Other code will reset the DAC.
 }
 
 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) {
+    #ifdef SAMD51
+    bool dac_clock_enabled = hri_mclk_get_APBDMASK_DAC_bit(MCLK);
+    #endif
+
+    #ifdef SAMD21
+    bool dac_clock_enabled = PM->APBCMASK.bit.DAC_;
+    #endif
+    // Only support exclusive use of the DAC.
+    if (dac_clock_enabled && DAC->CTRLA.bit.ENABLE == 1) {
+        mp_raise_RuntimeError("DAC already in use");
+    }
     #ifdef SAMD21
     if (right_channel != NULL) {
         mp_raise_ValueError("Right channel unsupported");
@@ -102,14 +112,10 @@ void common_hal_audioio_audioout_construct(audioio_audioout_obj_t* self,
     // SAMD51: This clock should be <= 350kHz, per datasheet table 37-6.
     _gclk_enable_channel(DAC_GCLK_ID, CONF_GCLK_DAC_SRC);
 
-    // There is a small chance the other output is being used by AnalogOut on the SAMD51 so
-    // only reset if the DAC is disabled.
-    if (DAC->CTRLA.bit.ENABLE == 0) {
+
         DAC->CTRLA.bit.SWRST = 1;
         while (DAC->CTRLA.bit.SWRST == 1) {}
 
-    }
-
     bool channel0_enabled = true;
     #ifdef SAMD51
     channel0_enabled = self->left_channel == &pin_PA02 || self->right_channel == &pin_PA02;
@@ -224,6 +230,14 @@ void common_hal_audioio_audioout_deinit(audioio_audioout_obj_t* self) {
         return;
     }
 
+    DAC->CTRLA.bit.ENABLE = 0;
+    #ifdef SAMD21
+    while (DAC->STATUS.bit.SYNCBUSY == 1) {}
+    #endif
+    #ifdef SAMD51
+    while (DAC->SYNCBUSY.bit.ENABLE == 1) {}
+    #endif
+
     disable_event_channel(self->tc_to_dac_event_channel);
 
     reset_pin(self->left_channel->pin);
@@ -320,9 +334,6 @@ void common_hal_audioio_audioout_stop(audioio_audioout_obj_t* self) {
     #ifdef SAMD51
     audio_dma_stop(&self->right_dma);
     #endif
-
-    // FIXME(tannewt): Do we want to disable? What if we're sharing with an AnalogOut on the 51?
-    // dac_disable(MP_STATE_VM(audioout_dac_instance));
 }
 
 bool common_hal_audioio_audioout_get_playing(audioio_audioout_obj_t* self) {

shared-bindings/audioio/RawSample.c

@@ -44,7 +44,7 @@
 //| .. class:: RawSample(buffer, *, channel_count=1, sample_rate=8000)
 //|
 //|   Create a RawSample based on the given buffer of signed values. If channel_count is more than
-//|   1 then each channel's samples should rotate. In other words, for a two channel buffer, the
+//|   1 then each channel's samples should alternate. In other words, for a two channel buffer, the
 //|   first sample will be for channel 1, the second sample will be for channel two, the third for
 //|   channel 1 and so on.
 //|

shared-bindings/audioio/WaveFile.c

@@ -39,7 +39,8 @@
 //| :class:`WaveFile` -- Load a wave file for audio playback
 //| ========================================================
 //|
-//| A .wav file prepped for audio playback
+//| A .wav file prepped for audio playback. Only mono and stereo files are supported. Samples must
+//| be 8 bit unsigned or 16 bit signed.
 //|
 //| .. class:: WaveFile(filename)
 //|