Add audiodelays & audioeffects to unix coverage port

.. and add a very basic audioeffects test, showing that it plausibly
is working

I had to address several build errors that occurred in the Unix build,
mostly related to conversion from FP types to integral types (replaced
by explicit casts) and by
accidental mixing of regular & f-suffixed floating constants (replaced
with the MICROPY_FLOAT_CONST macro)

Particularly this change could use consideration:
```diff
-    self->max_echo_buffer_len = self->sample_rate / 1000.0f * max_delay_ms * (self->channel_count * sizeof(uint16_t)); // bytes
+    self->max_echo_buffer_len = (uint32_t)(self->sample_rate / 1000.0f * max_delay_ms) * (self->channel_count * sizeof(uint16_t)); // bytes
```

The buffer length is being calculated in floating point based on the
millisecond delay & the sample rate. The result could then be a fractional
number such as 529.2 for a 12ms delay at 44.1kHz. Multiplying a floating
number by the size required for each echo buffer item
(`(self->channel_count * sizeof(uint16_t))`) could yield a number of bytes
that doesn't correspond to an integral number of buffer items. I grouped
the float->int conversion so that it converts the number of echo buffer
items to an integer and then multiplies by the size of the item.

ports/unix/variants/coverage/mpconfigvariant.mk

@@ -33,6 +33,10 @@ SRC_BITMAP := \
 	shared-bindings/audiocore/__init__.c \
 	shared-bindings/audiocore/RawSample.c \
 	shared-bindings/audiocore/WaveFile.c \
+	shared-bindings/audiodelays/Echo.c \
+	shared-bindings/audiodelays/__init__.c \
+	shared-bindings/audiofilters/Filter.c \
+	shared-bindings/audiofilters/__init__.c \
 	shared-bindings/audiomixer/__init__.c \
 	shared-bindings/audiomixer/Mixer.c \
 	shared-bindings/audiomixer/MixerVoice.c \
@@ -70,6 +74,10 @@ SRC_BITMAP := \
 	shared-module/audiocore/__init__.c \
 	shared-module/audiocore/RawSample.c \
 	shared-module/audiocore/WaveFile.c \
+	shared-module/audiodelays/Echo.c \
+	shared-module/audiodelays/__init__.c \
+	shared-module/audiofilters/Filter.c \
+	shared-module/audiofilters/__init__.c \
 	shared-module/audiomixer/__init__.c \
 	shared-module/audiomp3/MP3Decoder.c \
 	shared-module/audiomixer/Mixer.c \
@@ -127,6 +135,9 @@ $(BUILD)/lib/mp3/src/buffers.o: CFLAGS += -include "shared-module/audiomp3/__ini
 CFLAGS += \
 	-DCIRCUITPY_AESIO=1 \
 	-DCIRCUITPY_AUDIOCORE=1 \
+	-DCIRCUITPY_AUDIOEFFECTS=1 \
+	-DCIRCUITPY_AUDIODELAYS=1 \
+	-DCIRCUITPY_AUDIOFILTERS=1 \
 	-DCIRCUITPY_AUDIOMIXER=1 \
 	-DCIRCUITPY_AUDIOMP3=1 \
 	-DCIRCUITPY_AUDIOMP3_USE_PORT_ALLOCATOR=0 \

shared-module/audiodelays/Echo.c

@@ -77,7 +77,7 @@ void common_hal_audiodelays_echo_construct(audiodelays_echo_obj_t *self, uint32_
 
     // Allocate the echo buffer for the max possible delay, echo is always 16-bit
     self->max_delay_ms = max_delay_ms;
-    self->max_echo_buffer_len = self->sample_rate / 1000.0f * max_delay_ms * (self->channel_count * sizeof(uint16_t)); // bytes
+    self->max_echo_buffer_len = (uint32_t)(self->sample_rate / 1000.0f * max_delay_ms) * (self->channel_count * sizeof(uint16_t)); // bytes
     self->echo_buffer = m_malloc(self->max_echo_buffer_len);
     if (self->echo_buffer == NULL) {
         common_hal_audiodelays_echo_deinit(self);
@@ -129,11 +129,11 @@ void common_hal_audiodelays_echo_set_delay_ms(audiodelays_echo_obj_t *self, mp_o
 void recalculate_delay(audiodelays_echo_obj_t *self, mp_float_t f_delay_ms) {
     if (self->freq_shift) {
         // Calculate the rate of iteration over the echo buffer with 8 sub-bits
-        self->echo_buffer_rate = MAX(self->max_delay_ms / f_delay_ms * 256.0f, 1.0);
+        self->echo_buffer_rate = (uint32_t)MAX(self->max_delay_ms / f_delay_ms * MICROPY_FLOAT_CONST(256.0), MICROPY_FLOAT_CONST(1.0));
         self->echo_buffer_len = self->max_echo_buffer_len;
     } else {
         // Calculate the current echo buffer length in bytes
-        uint32_t new_echo_buffer_len = self->sample_rate / 1000.0f * f_delay_ms * (self->channel_count * sizeof(uint16_t));
+        uint32_t new_echo_buffer_len = (uint32_t)(self->sample_rate / MICROPY_FLOAT_CONST(1000.0) * f_delay_ms) * (self->channel_count * sizeof(uint16_t));
 
         // Check if our new echo is too long for our maximum buffer
         if (new_echo_buffer_len > self->max_echo_buffer_len) {
@@ -153,7 +153,7 @@ void recalculate_delay(audiodelays_echo_obj_t *self, mp_float_t f_delay_ms) {
         memset(self->echo_buffer + self->echo_buffer_len, 0, self->max_echo_buffer_len - self->echo_buffer_len);
     }
 
-    self->current_delay_ms = f_delay_ms;
+    self->current_delay_ms = (uint32_t)f_delay_ms;
 }
 
 mp_obj_t common_hal_audiodelays_echo_get_decay(audiodelays_echo_obj_t *self) {
@@ -360,17 +360,17 @@ audioio_get_buffer_result_t audiodelays_echo_get_buffer(audiodelays_echo_obj_t *
                         echo = echo_buffer[echo_buffer_pos >> 8];
                         next_buffer_pos = echo_buffer_pos + self->echo_buffer_rate;
 
-                        word = echo * decay;
+                        word = (int16_t)(echo * decay);
                         for (uint32_t j = echo_buffer_pos >> 8; j < next_buffer_pos >> 8; j++) {
                             echo_buffer[j % echo_buf_len] = word;
                         }
                     } else {
                         echo = echo_buffer[self->echo_buffer_read_pos++];
-                        word = echo * decay;
+                        word = (int16_t)(echo * decay);
                         echo_buffer[self->echo_buffer_write_pos++] = word;
                     }
 
-                    word = echo * mix;
+                    word = (int16_t)(echo * mix);
 
                     if (MP_LIKELY(self->bits_per_sample == 16)) {
                         word_buffer[i] = word;
@@ -433,10 +433,10 @@ audioio_get_buffer_result_t audiodelays_echo_get_buffer(audiodelays_echo_obj_t *
                     if (self->freq_shift) {
                         echo = echo_buffer[echo_buffer_pos >> 8];
                         next_buffer_pos = echo_buffer_pos + self->echo_buffer_rate;
-                        word = echo * decay + sample_word;
+                        word = (int32_t)(echo * decay + sample_word);
                     } else {
                         echo = echo_buffer[self->echo_buffer_read_pos++];
-                        word = echo * decay + sample_word;
+                        word = (int32_t)(echo * decay + sample_word);
                     }
 
                     if (MP_LIKELY(self->bits_per_sample == 16)) {
@@ -467,12 +467,12 @@ audioio_get_buffer_result_t audiodelays_echo_get_buffer(audiodelays_echo_obj_t *
                     word = echo + sample_word;
 
                     if (MP_LIKELY(self->bits_per_sample == 16)) {
-                        word_buffer[i] = (sample_word * (1.0 - mix)) + (word * mix);
+                        word_buffer[i] = (int16_t)((sample_word * (1.0 - mix)) + (word * mix));
                         if (!self->samples_signed) {
                             word_buffer[i] ^= 0x8000;
                         }
                     } else {
-                        int8_t mixed = (sample_word * (1.0 - mix)) + (word * mix);
+                        int8_t mixed = (int16_t)((sample_word * (1.0 - mix)) + (word * mix));
                         if (self->samples_signed) {
                             hword_buffer[i] = mixed;
                         } else {

shared-module/audiofilters/Filter.c

@@ -204,6 +204,7 @@ int16_t mix_down_sample(int32_t sample) {
 
 audioio_get_buffer_result_t audiofilters_filter_get_buffer(audiofilters_filter_obj_t *self, bool single_channel_output, uint8_t channel,
     uint8_t **buffer, uint32_t *buffer_length) {
+    (void)channel;
 
     if (!single_channel_output) {
         channel = 0;
@@ -297,15 +298,15 @@ audioio_get_buffer_result_t audiofilters_filter_get_buffer(audiofilters_filter_o
                     // Mix processed signal with original sample and transfer to output buffer
                     for (uint32_t j = 0; j < n_samples; j++) {
                         if (MP_LIKELY(self->bits_per_sample == 16)) {
-                            word_buffer[i + j] = mix_down_sample((sample_src[i + j] * (1.0 - mix)) + (self->filter_buffer[j] * mix));
+                            word_buffer[i + j] = mix_down_sample((int32_t)((sample_src[i + j] * (MICROPY_FLOAT_CONST(1.0) - mix)) + (self->filter_buffer[j] * mix)));
                             if (!self->samples_signed) {
                                 word_buffer[i + j] ^= 0x8000;
                             }
                         } else {
                             if (self->samples_signed) {
                                 hword_buffer[i + j] = (int8_t)((sample_hsrc[i + j] * (1.0 - mix)) + (self->filter_buffer[j] * mix));
                             } else {
-                                hword_buffer[i + j] = (uint8_t)(((int8_t)(((uint8_t)sample_hsrc[i + j]) ^ 0x80) * (1.0 - mix)) + (self->filter_buffer[j] * mix)) ^ 0x80;
+                                hword_buffer[i + j] = (uint8_t)(((int8_t)(((uint8_t)sample_hsrc[i + j]) ^ 0x80) * (MICROPY_FLOAT_CONST(1.0) - mix)) + (self->filter_buffer[j] * mix)) ^ 0x80;
                             }
                         }
                     }

tests/circuitpython/audiofilter_filter.py

@@ -0,0 +1,16 @@
+from audiofilters import Filter
+from audiofilterhelper import synth_test, sine8k
+
+@synth_test
+def basic_filter():
+    effect = Filter(
+        bits_per_sample=16,
+        samples_signed=True,
+    )
+    yield effect, []
+
+    effect.play(sine8k, loop=True)
+    yield 4
+
+    effect.stop()
+    yield 2